MINISTRY OF AGRICULTURE, FISHERIES AND FOOD CSG 15Research and Development

Final Project Report(Not to be used for LINK projects)

Two hard copies of this form should be returned to:Research Policy and International Division, Final Reports UnitMAFF, Area 6/011A Page Street, London SW1P 4PQ

An electronic version should be e-mailed to c.csgfinrep@csg.maff.gsi.gov.uk

Project title Dietary strategies to enhance the fatty acid composition of milk     

MAFF project code LS1803

Contractor organisation and location

ADAS Bridgets Dairy Research CentreMartyr WorthyWinchester, Hants., SO21 1AP

Total MAFF project costs £ 645,656

Project start date 01/10/97 Project end date 31/03/01

Executive summary (maximum 2 sides A4)

The health strategy for the UK into the next millennium was outlined in the Government’s Health of the Nation paper, while the COMA report on the ‘Nutritional Aspects of Cardiovascular Disease’ made a number of specific recommendations aimed at reducing the incidence of coronary heart disease. These included advice to reduce intake of total fat; reduce the proportion of dietary energy derived from saturated fatty acids (SFA); ensure that diets containing high levels of polyunsaturated fatty acids (PUFA) were adequately supplied with vitamin E; avoid any increase in n-6 PUFA; increase consumption of long chain n-3 PUFA and consider ways of reducing the amount of trans fatty acids in the diet. Prominent medical experts have since indicated that consumption of n-3 PUFA (as C18:3), monounsaturated fatty acids (MUFA) and selenium (Se) should also increase while intake of specific SFA’s (C14:0 and C16:0) should fall. Daily intake of Se in the UK has declined steadily and is now below levels considered as necessary to maintain optimum enzyme function. Health professionals and policy makers are investigating alternative methods of increasing Se intake by increasing concentrations in staple foods. Typically, UK bovine milk and milk products can be regarded as major dietary sources of fat, SFA (including C14 and C16), and trans fatty acids while contributing only small amounts of MUFA, n-3 PUFA, vitamin E or Se to the diet. The overall objective of the work was to enhance the role of bovine milk in achieving the Health of the Nation objectives by developing appropriate feeding strategies for dairy cows, which modified milk fatty acid and antioxidant content.

Overall conclusions and recommendations

1. A reduction in the concentration of C14:0 + C16:0 (by 46%) and an increase in the concentration of C18:1 in milk fat (by 192%) was achieved when whole cracked rapeseed was used to supplement dairy cow diets (185 g supplement/kg diet DM). There was however associated depression of dry matter intake, milk yield and milk fat content. The long-term effects of supplementing dairy cow diets CSG 15 (Rev. 12/99) 1

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

with whole cracked rapeseed on economic performance and cow health and fertility warrant further investigation. A reduction in the concentration of C14:0 + C16:0 (by 37%) in milk fat was also achieved when xylose treated whole soya was used to supplement diets and this was not associated with reductions in DM intake or milk yield.

2. The efficiency of transfer of dietary supplementation of synthetic vitamin E to milk was greater for the whole rapeseed diets compared with xylose treated linseed though the reason for this is unclear and requires further investigation.

3. An increase in the concentration of C18:3(n-3) in milk fat (by 214%) was achieved when xylose and heat treated whole linseed was used to supplement diets (97 g supplement/kg diet DM). At this level of inclusion there was no effect on DM intake and milk fat, but there was an increase in milk yield and a decline in milk protein. Vitamin E supplementation at 6g/cow/day did not influence the milk fatty acid composition although it did increase milk vitamin E concentrations. There were no adverse effects on milk taste. C18:3(n-3) concentration in milk fat was shown to increase further with increased levels of supplementation with xylose treated whole linseed but to the detriment of milk yield and fat concentration. Processing methods require development to protect the rumen further from the negative effects of linseed oil on fibre degradability.

4. The fatty acid composition of the milk changed over the duration of the study with increasing levels of C18:1(n-7) trans and decreased the concentration of C18:2(n-6) cis. This suggests that an adaptation to the diet or an effect of stage of lactation may change rumen metabolism, gut uptake or fatty acid partition between milk and tissues. This requires further investigation.

5. The vitamin E content of milk can be increased with dietary supplementation with synthetic vitamin E. The efficiency of uptake into milk was poor and was reduced further with increasing dietary supplementation. The sources of rumen protected synthetic vitamin E currently available do not improve the efficiency of uptake. Further studies are necessary to determine fully those factors limiting the secretion of vitamin E into milk and to identify the potential to enhance further the vitamin E content of bovine milk.

6. The selenium concentration in milk can be increased up to 10 times the mean concentration currently recorded for milk using an organic form of selenium (selenium yeast) currently not authorised for use within the EU. Further studies are required with organic selenium to develop response curves to different levels of supplementation to achieve target milk selenium concentration whilst remaining within the permitted EU dietary concentrations. Further work is also required to determine whether or not increasing milk selenium concentration is sustainable throughout an entire lactation and to establish the effects on dairy cow health, fertility and performance.

7. The model published by Hermensen (1995) did not provide satisfactory predictors of the concentrations of milk fatty acids C12 to C18 with the data from these studies. It was concluded that this was likely due to the inclusion of protected fats in the studiesused to derive the model. It is recommended that more complex and far reaching models to predict milk fatty acid composition be researched, to include a greater range of dietary inputs than used in this study.

CSG 15 (1/00) 2

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Scientific report (maximum 20 sides A4)The health strategy for the UK into the next millennium was outlined in the Government’s Health of the Nation paper, while the COMA report on the ‘Nutritional Aspects of Cardiovascular Disease’ made a number of specific recommendations aimed at reducing the incidence of coronary heart disease. These included advice to reduce intake of total fat; reduce the proportion of dietary energy derived from saturated fatty acids (SFA); ensure that diets containing high levels of polyunsaturated fatty acids (PUFA) were adequately supplied with vitamin E; avoid any increase in n-6 PUFA; increase consumption of long chain n-3 PUFA and consider ways of reducing the amount of trans fatty acids in the diet. Prominent medical experts have since indicated that consumption of n-3 PUFA (as C18:3), monounsaturated fatty acids (MUFA) and selenium (Se) should also increase while intake of specific SFA’s (C14:0 and C16:0) should fall. Typically, UK bovine milk and milk products can be regarded as major dietary sources of fat, SFA (including C14 and C16), and trans fatty acids while contributing only small amounts of MUFA, n-3 PUFA, vitamin E or Se to the diet. However, work at ADAS Bridgets has previously shown that the fatty acid composition of milk fat can be modified by appropriate feeding strategies, to produce milk which is healthier and more likely to contribute to the Health of the Nation objectives. The overall objective of this work was to enhance the role of bovine milk in achieving the Health of the Nation objectives by developing appropriate feeding strategies for dairy cows, which modified milk fatty acid and antioxidant content.

The objectives of the work were:1. Reduce concentrations of C14:0 and C16:0 fatty acids by reviewing dietary factors affecting their levels in milk and investigating these strategies in dairy cow production studies.2. Increase concentrations of C18:3 (n-3) in milk3. Increase concentrations of C18:1 in milk4. Increase concentrations of vitamin E in milk by dietary supplementation5. Increase concentrations of selenium in milk by dietary supplementation6. Increase concentrations of natural antioxidants by reviewing sources7. Use the data from objectives 1, 2 and 3 to test against the model published by Hermansen (1995)

1. Reduce levels of C14:0 and C16:0

Current medical thinking suggests that the saturated fatty acids myristic (C14:0) and palmitic (C16:0) are particularly harmful compared with longer chain fatty acids such as stearic (C18:0) and oleic (C18:1). Milk fat is rich in C14:0 and C16:0 because these fatty acids can be manufactured in the bovine mammary gland from glycerol and free fatty acids. All low and medium molecular weight fatty acids (up to and including 50% of palmitic acid) in milk are produced by de-novo synthesis from acetate and -hydroxybutyrate; while all the higher molecular weight fatty acids and the remaining palmitic acid are obtained from the diet. Earlier work (Hermansen, 1995; Gulati et al., 1997) has shown that the levels of C16:0 in milk can be lowered by changes to diet, whereas it has proved more difficult to alter the levels of C14:0. Two studies were done to investigate whether or not manipulating the diet of dairy cows was a potential method to lower levels of C14:0 and C16:0 in milk fat.

Study 1

In a randomised block design, six dietary oil sources (whole ground soya beans (UWS) - 237g oil/kg dry matter (DM); whole ground soya beans treated with xylose (supplied by Borregaard UK Ltd.) (TWS) - 191 g oil/kg DM)); whole ground rapeseed ((WR) - 452 g oil/kg DM), a combination of UWS + TWS (0.5:0.5), a combination of TWS + WR (0.66:0.33) and a Control (containing no additional oil source) were fed to 72 multiparous Holstein cows (12 cows per treatment, average weight at the start 620 kg) for eight weeks in early lactation. Total mixed rations consisted of a fixed level of grass silage (7.5 kg DM), various amounts of ground wheat, sugar beet feed, soya bean meal and rape seed meal (Control) or plus 7.1 kg DM UWS, 7.1 kg DM TWS, 3.6 kg DM WR, 3.6 kg DM each of UWS and TWS or 3.6 kg DM TWS and 1.8 kg DM WR. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 35 litres with 0.5 kg/d weight loss. Data were analysed using ANOVA, with a Dunnetts test for significance between the TWS and the other treatments.

CSG 15 (1/00) 3

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Animal performance results are presented in Table 1 and milk fatty acid composition in Table 2. Feeding TWS reduced intake compared with control, while milk yield was increased. WS reduced milk yield but had similar intakes compared with TWS, while there were no differences in intake and yield between WR and TWS. There was no effect of TWS or WS on milk fat content, although levels were reduced by WR. Levels of C14:0 and C16:0 were lower than Control with TWS while C18:0, C18:1 and C18:2 were higher. Feeding WS produced similar changes to TWS except that C18:2 level was lower. WR reduced C16:0 and C18:2, and increased C18:1 compared with TWS.

Table 1: Intake (kg DM/d), milk yield (kg/d) and milk fat content (g/kg milk)Control TWS UWS WR UWS+

TWSTWS+

WRs.e. Control1 UWS1 WR1 UWS+

TWS1TWS+WR1

Intake 20.5 19.2 18.7 19.0 20.0 20.5 0.33 * NS NS NS *Yield 30.5 36.0 30.9 34.6 34.4 36.7 0.80 ** ** NS NS NSMilk fat 42.5 45.6 44.8 32.9 41.4 36.8 1.56 NS NS ** NS **

Table 2: Milk fatty acid composition (g/100g total fatty acid)Control TWS UWS WR UWS+

TWSTWS+

WRs.e. Control1 UWS1 WR1 UWS+

TWS1TWS+WR1

C14:0 12.2 8.3 9.0 8.1 8.6 7.8 0.23 ** NS NS NS NSC16:0 34.8 21.3 22.2 17.3 21.1 18.1 0.52 ** NS ** NS **C18:0 7.2 15.5 17.5 16.3 17.3 16.7 0.59 ** NS NS NS NSC18:1(n9)

13.7 21.3 22.5 32.5 21.9 27.6 0.76 ** NS ** NS **

C18:2(n6)

1.9 7.5 4.5 2.6 5.5 4.6 0.27 ** ** ** ** **

1 Compared with TWS, NS not significant, * p<0.05, ** p<0.01

Feeding TWS reduced C14:0 and C16:0 levels and increased C18 fatty acids in milk fat while improving milk yield. UWS had similar effects on milk fatty acid composition, although there was no increase in milk yield. WR reduced milk fat content, and further decreased C16:0 and increased C18:1. Feeding mixtures of TWS with either UWS or WR gave changes in milk fatty acid composition intermediary to when they were fed alone. Overall, WR reduced C14:0 + C16:0 to 25g/100g milk fatty acid compared with 47g/100g milk fatty acid in the control milk. Despite the WR producing the lowest level of C14.0+ C16.0, the whole rape significantly reduced milk fat level. Further work to protect the rumen from the negative nature of whole rapeseed on fibre degradation is needed to control this effect. The results suggest that feeding specific sources of dietary oil can dramatically reduce levels of C14:0 and C16:0 in milk fat.

Study 2

In a 3 x 3 factorial design, three dietary oil sources, rape expeller treated with xylose (XRE); rape expeller heat treated (HRE); and heat treated cracked whole rapeseed with ground beans (HRB) were fed to 63 multiparous and 27 primiparous Holstein cows. There were 10 cows per treatment (average weight at start of 620 kg) which were fed at three levels of inclusion ((85, 174 and 270 g/kg DM (L, M or H respectively)) for 8 weeks in early lactation. Total mixed rations consisted of a fixed level of grass and maize silage and various amounts of ground wheat, sugar beet feed, soya bean meal and rapeseed meal. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 35 litres with 0.5 kg/d weight loss. Data were analysed using repeated measures ANOVA, to establish the effect of the lipid supplement used, its rate of inclusion in the diet and the interaction between lipid source and rate of inclusion on the performance of the cows.

CSG 15 (1/00) 4

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Animal performance results are presented in Table 3 and milk fatty acid composition in Table 4. There was a significant (P<0.001) interaction between the lipid supplement and the level of its inclusion in the diet of cows dry matter intake. Increasing the inclusion level of lipid supplement significantly reduced dry matter intake and intake was usually higher for HRE. Milk yield and the concentration of milk fat was lower for HRB compared with the other lipid supplements and for all lipid supplements an increased inclusion level decreased both milk yield and milk fat content. The source of the lipid supplement did not affect the milk fat content for C16:0 but there was a significant effect of supplement source for C14:0, with HRB, HRE and XRE having increasing C14:0 contents respectively. Increasing level of supplement only decreased the C14:0 content of milk fat. HRB was most effective in reducing C14:0 content of milk, but the C16:0 content was not affected by the type of supplement. Feeding HRB also resulted in the lowest DM intake, milk yield and milk fat content, which suggests that the lipid in HRB may have been less protected than in the other supplements.

Table 3: Intake (kg DM/d), milk yield (kg/d) and milk fat content (g/kg milk)LXRE MXRE HXRE LHRE MHRE HHRE LHRB MHRB HHRB Significance

Source Level Source xlevel

Intake 21.5 21.5 21.8 22.2 22.5 21.5 21.9 20.8 20.9 *** * ***Yield 38.8 37.7 36.1 37.3 37.4 35.6 35.7 34.9 34.9 *** *** NSMilk fat

30.4 26.4 28.4 32.6 30.9 27.3 28.8 25.2 26.1 * * NS

Table 4: Milk fatty acid composition (g/100g total fatty acid)LXRE MXRE HXRE LHRE MHRE HHRE LHRB MHRB HHRB Significance

Source Level Source xlevel

C14:0 10.3 10.2 9.0 8.6 9.0 8.2 7.9 7.9 7.6 ** *** NSC16:0 21.6 20.9 19.8 18.8 18.2 19.2 17.1 17.5 16.7 NS *** NS

NS not significant, * p<0.05, ** p<0.01, *** P<0.001

Milk in the UK typically contains about 11.0 and 27.0 g/100g total fat of C14:0 and C16:0 respectively (McCance and Widdowson, 1998). All treatments produced values lower than these and increasing lipid supplements decreased the concentration of C14:0 and C16:0 in both whole milk and the fatty acid fraction of the milk. More work is required on lipid treatment techniques for naturally lipid-rich feeds to prevent the deleterious effects in the rumen.

2. Increase levels of C18:3 (n-3) in milk

High levels of polyunsaturated fatty acids (particularly eicosapentaenoic C20:5 (n-3) and docosahexaenoic C22:6 (n-3) acids) are thought to protect against cardiovascular disease. There is some evidence that -linolenic acid (C18:3(n3)) can be elongated and desaturated by mammalian enzyme systems to produce small amounts of C20:5 and C22:6. Typically, while UK bovine milk and milk products can be regarded as major dietary sources of fat, they contribute only small amounts of C18:3(n-3) to the human diet. Plants, unlike animals, can synthesise C18:3(n-3) de novo, and consequently the lipid fraction of all green plant material, such as grass, is rich in this fatty acid. Many UK dairy cow diets have a high proportion of forage and therefore sizeable intakes of C18:3(n-3) but the majority is likely to undergo biohydrogenation in the rumen to more saturated fatty acids. Several workers (Hebeisen et al., 1993; Mpelimpasakes, 1981) have reported that the nature of the dietary forage can affect transfer of C18:3(n-3) into milk. Cows fed herb rich fresh grass gave milk containing higher levels of C18:3(n-3) than cows fed hay; and cows fed hay produced higher C18:3(n-3) levels in the milk than cows fed grass silage. There is evidence (Scollan et al, 1997) that feeding a diet rich in C18:3(n-3) to steers, increased the levels of eicosapentaenoic acid (EPA; C20:5(n-3)) and docosahexaenoic acid (DHA; C22:6(n-3)) in muscle tissue to the same extent as a diet rich in EPA and DHA. Therefore three studies were done to investigate dietary methods to increase levels of C18:3(n-3) in milk fat and to investigate the optimum levels of vitamin E for high C18:3(n-3) milk.

CSG 15 (1/00) 5

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Study 1

In a randomised block design, whole ground linseed (WL) (335g oil/kg dry matter (DM)), whole ground linseed treated with xylose (supplied by Borregaard UK Ltd.)(TWL) (342g oil/kg DM), dried grass meal and a Control (containing no additional oil source) were fed to 48 Holstein cows for eight weeks in early lactation. There were 12 cows per treatment (average weight at start 633 kg). Total mixed rations consisted of a fixed level of grass silage (10.0 kg DM), various amounts of ground wheat, sugar beet feed, soya bean meal and rape seed meal (Control) or plus 1.8 kg DM WL, 1.8 kg DM TWL, 9.0 kg DM Dried grass + 3 kg DM grass silage. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 35 litres and 0.5 kg/d weight loss (AFRC, 1993). Data were analysed using ANOVA, with a Dunnetts test for significance between the TWL and the other treatments.

Animal performance results are presented in Table 5 and milk fatty acid composition in Table 6 for the linseed treatments. Feeding TWL had no effect on intake, milk yield or milk fat content compared with the Control. Intake and milk fat content in WL was similar to TWL, but yield was significantly lower. Levels of C16:0 were lower than Control with TWL while concentrations of C18:0, C18:1, C18:2 and C18:3 were higher. Feeding WL produced similar changes to TWL except that C18:3 level was lower. There was no evidence of C20:5 or C22:6 fatty acids in milk fat from any treatment.

Table 5: Intake (kg DM/d), milk yield (kg/d) and milk fat content (g/kg milk)Control WL TWL s.e. Control1 WL1

Intake 19.1 18.2 18.8 0.32 NS NSYield 33.7 31.5 35.3 0.99 NS **Milk fat 43.8 42.2 42.2 1.56 NS NS

Table 6: Milk fatty acid composition (g/100g total fatty acid)Control WL TWL s.e. Control1 WL1

C16:0 30.9 23.9 24.1 0.52 ** NSC18:0 9.5 15.0 17.5 0.59 ** NSC18:1(n-9) 14.5 19.3 18.6 0.85 ** NSC18:2(n-6) 1.5 1.8 2.0 0.07 ** NSC18:3(n-3) 0.7 1.2 1.5 0.05 ** **

1 Compared with TWL, NS not significant, ** P<0.01

Feeding TWL increased the level of all C18 fatty acids in milk fat while maintaining milk yield and milk fat content. WL had similar effects on milk fatty acid composition except C18:3(n-3) level was lower than in cows fed TWL. The reduction of C18:3(n-3) and milk yield in cows fed WL compared with TWL suggests that the xylose treatment may protect some of the oil within whole linseed from rumen microbial action. Although feeding TWL doubled the level of C18:3(n-3) in milk fat compared with the control diet, the proportion was still less than 2g/100g milk fatty acid. There was no evidence of C20:5 and C22:6 in milk fat, suggesting that if any elongation and desaturation of C18:3(n-3) does occur in dairy cows, none is transferred to milk.

The dried grass treatment initially (weeks 1 to 4) contained no other forage source, but resulted in dramatic reductions in DM intake and milk yield. Grass silage was introduced into the diet replacing 25% (DM basis) of the dried grass (weeks 5 to 8), DM intake and milk yields increased rapidly to above and equal to the control respectively. The dried grass + grass silage treatment significantly increased the levels of C18:1(n7) (2.96 g/100g total fat), C18:2(conjugated) (2.0g/100g total fat) and C18:3(n-3) ( 1.0g/100g total fat) in milk fat but did not alter the level of C18:2(n-6).

Feeding 2 kg (as fed)/head/day xylose-treated whole cracked linseed resulted in significantly more C18:3(n-3) in milk fat than feeding similar levels of untreated whole cracked linseed or dried grass + grass silage. The efficiency of incorporation of the ‘extra’ dietary C18:3(n-3) into milk fat was 1.6% and 3.4% for untreated and xylose-treated cracked linseed respectively, suggesting that the oil in the xylose-treated linseed had improved rumen protection.

Study 2

CSG 15 (1/00) 6

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Free radicals are highly reactive molecules, which are generated during many metabolic processes and have been associated with potentially fatal medical conditions such as coronary heart disease. Antioxidants, such as vitamin E, are chemicals which can prevent the damaging effects of free radicals on body cells, and its’ content in blood has been inversely correlated with coronary heart disease. Milk in the UK contains on average 0.9 mg vitamin E/kg, but research suggests that milk concentration can be increased two-fold by supplementation with vitamin E in dairy cow rations. However, the actual level varies with seasonal change in vitamin E intake, milk fat content and the efficiency of transfer across the mammary gland. Work from Italy (Cheli et al., 1995) showed a two-folds increase in the level of vitamin E in milk when 5 g DL--tocopheryl acetate was fed. Work done at ADAS Bridgets has shown that supplementation with 1 g DL--tocopheryl acetate/d failed to increase vitamin E levels in the milk (Mansbridge, 1997) but, supplementation at higher levels (2 and 4 g DL--tocopheryl acetate/d) led to increased milk vitamin E content (Allison, 2000).

Changing the fatty acid profile of lactating cow diets can lead to significant improvements to the fatty acid content of milk, which may have significant human health benefits. For example, feeding whole rape seed led to a 54% reduction in the saturated fatty acids C14:0 and C16:0 (Mansbridge 1999) and a 40% increase in the C18:1 content of milk (Allison, 2000), while feeding 2 kg/cow/d whole linseed led to a 100% increase in the C18:3 content (Mansbridge, 1999). However, whole oilseeds contain large amounts of PUFA, which may increase the risk of lipid oxidation within animal tissue, and thereby increase the requirement for vitamin E in the dairy cow (Allison and Laven, 2000; Herdt and Stowe, 1991). Current UK and US recommendations for vitamin E for dairy cows do not take PUFA intake into account, despite responses having been shown to additional vitamin E when oilseeds are included in dairy cow rations (Lundin and Palmquist, 1983).

In a previous study (Mansbridge, 1999), feeding xylose treated whole linseed had no effect on animal performance compared with untreated linseed, and led to an increase in the PUFA content of milk. This study examined the relationship between vitamin E supplementation of dairy cow diets and the vitamin E content of milk, when high levels of polyunsaturated fatty acids (from treated whole linseed) were fed.

In a randomised block design whole ground linseed treated with xylose (supplied by Borregaard UK Ltd.)(TWL) (342g oil/kg DM) and one of four levels of additional vitamin E (Lutavit E 50; 50% DL--tocopherol acetate, BASF) (0, 2, 4 and 6 g/cow/d) were fed to 48 Holstein cows for eight weeks in early lactation. There were 12 cows per treatment (average weight at start 608 kg). Total mixed rations consisted of a fixed level of treated whole linseed (1.84 kg DM) and grass silage (10.0 kg DM), various amounts of ground wheat, sugar beet feed, soya bean meal and rape seed meal and the appropriate amount of Vitamin E supplementation. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 30 litres and 0.5 kg/d weight loss (AFRC, 1993). Data were analysed using repeat measures ANOVA.

Animal performance results are presented in Table 7 and milk fatty acid composition in Table 8 for the vitamin E treatments. Feeding increasing levels of vitamin E had no effect on intake, milk yield or milk fat content compared with the Control. Milk fatty acid composition was unaffected by vitamin E level. Supplementing the diet with vitamin E significantly increased its level in milk.

Table 7: Intake (kg DM/d), milk yield (kg/d), milk fat content (g/kg milk) and DL--tocopheryl acetate (mg/kg) content in milk

Vitamin E supplement (g/head/d) s.e. P value0 2 4 6

Intake 19.4 19.6 19.6 19.4 0.49 NSYield 32.1 30.9 30.4 29.6 0.80 NSMilk fat 40.7 43.0 43.2 42.8 1.49 NSDL--tocopheryl acetate

0.80 1.07 1.16 1.38 0.056 ***

Table 8: Milk fatty acid composition (g/100g total fatty acid)Vitamin E supplement (g/head/d) P value

0 2 4 6C16:0 23.7 24.8 25.1 25.2 NS

CSG 15 (1/00) 7

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

C18:0 13.1 12.9 12.5 12.7 NSC18:1(n-9) 18.7 19.1 17.4 17.5 *C18:2(n-6) 1.7 1.7 1.6 1.6 NSC18:3(n-3) 1.4 1.3 1.4 1.4 NS

NS not significant, * P<0.05, *** P<0.001

Feeding treated whole linseed produced milk with lower levels of C14:0 and C16:0, and higher levels of C18:0, C18:1(n-9) cis and C18:3(n-3) cis than standard milk. Consequently, levels of monounsaturated and polyunsaturated fatty acids were increased, while levels of saturated fatty acids were reduced compared with standard bovine milk. This result was in good agreement with the findings of study 1. Similar to study 1 where whole linseed was fed, there was an effect of time which increased levels of C18:1(n-7) trans and decreased the concentration of C18:2(n-6) cis although the changes were significant but small. This suggests that an adaptation to the diet or an effect of stage of lactation may change rumen metabolism, gut uptake or fatty acid partition between milk and tissues. The uptake of dietary vitamin E into milk in this experiment was poor with a mean efficiency of 2.4 mg/g dietary vitamin E. In a previous study (Allison, 2000), transfer efficiencies although higher at 13 mg/g and 50 mg/g, were still low overall (< 6%). The reasons for this inefficiency are unclear. Recent experiments in vitro suggest that vitamin E may not be degraded in the rumen (Leedle et al., 1993; Weiss et al., 1995), although earlier work (Alderson et al., 1971) reported the destruction of approximately 40% when diets high in maize grain were fed. This issue remains unresolved and further research is required to clarify the situation.

Study 3

The aim of the present study was to investigate the response to feeding to dairy cows increasing quantities of treated linseed, rich in -linolenic acid, on n-3 PUFA concentrations of milk fat. The effects on other fatty acids were also examined. In addition, the effects of dietary supplementation with vitamin E on the vitamin E and fatty acid composition of the milk was also examined as was the effect of supplementary vitamin E on the oxidative stability and taste of the milk.

In a 3 x 2 factorial design, level of inclusion of whole ground linseed treated with xylose (supplied by Borregaard UK Ltd.) (301g oil/kg DM) (78, 142 and 209 g lipid supplement/kg diet DM, LL, ML or HL respectively) was investigated with two levels of additional vitamin E (Rovimix E-50 adsorbate) (6 and 12 g/cow/d, LE or HE respectively) were fed to 60 Holstein cows for eight weeks in early lactation. There were 10 cows per treatment (average weight at start 618 kg). Total mixed rations consisted of a fixed level of grass silage (11.0 kg DM), various amounts of ground wheat, sugar beet feed, soya bean meal and rapeseed meal plus either 1.8 kg DM, 3.2 kg DM or 4.6 kg DM of treated whole linseed and either 6 or 12g vitamin E. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 30 litres and 0.5 kg/d weight loss (AFRC, 1993). Data were analysed using repeat measures ANOVA.

Animal performance results are presented in Table 9 and milk fatty acid composition in Table 10 for the treated linseed and vitamin E treatments. Feeding increasing levels of vitamin E had no effect on intake, milk yield or milk fat content. Feeding increasing levels of treated linseed significantly decreased DM intake, milk yield and milk protein content. There were no significant interactions between level of lipid supplement and vitamin E for the aforementioned parameters. There was, however, a significant lipid and vitamin E supplement interaction for the vitamin E content of the milk. Increasing levels of lipid supplementation significantly decreased the vitamin E content of the milk at the 6g/d inclusion of vitamin E whereas vitamin E content of milk was unaffected by increasing lipid supplementation at the higher inclusion of vitamin E Milk fatty acid composition was unaffected by vitamin E level. There was a significant increase in the C18 unsaturated fatty acids and decrease in the saturated fatty acids in the milk fat with increasing inclusion of the lipid supplement, but no effect of vitamin E supplementation.

Table 9 Intake, milk yield, milk composition and DL--tocopheryl acetate content in milk

Experiment diet SignificanceParameter LLLE MLLE HLLE LLHE MLHE HLHE Level of

lipidLevel of

vitamin ELipid x vitamin

E

CSG 15 (1/00) 8

Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

DM intake (kg/d) 19.0 18.4 17.2 19.6 18.5 17.3 ** NS NSMilk yield (kg/d) 28.4 26.2 25.2 28.0 26.3 26.0 ** NS NS

Milk compositionFat (g/kg) 41.0 44.9 43.8 44.4 45.5 42.8 NS NS NSProtein (g/kg) 33.0 33.0 32.0 32.7 33.3 31.4 ** NS NSVitamin E (mg/kg) 1.94 1.66 0.99 1.76 1.65 1.74 *** NS ***Yield of milk constituents (kg/d)Fat 1.17 1.18 1.09 1.30 1.13 1.19 NS NS NSProtein 0.91 0.88 0.80 0.93 0.84 0.86 ** NS NSNS not significant, ** P<0.01, *** P<0.001.

Table 10 Milk fatty acid composition (g/100g total fatty acid)Experiment diet Significance

Milk fatty acid LLLE MLLE HLLE LLHE MLHE HLHE Level of lipid

Level of vitamin

E

Lipid x vitamin

EC14:0 10.1 9.0 8.0 10.3 9.2 7.8 *** NS NSC16:0 23.1 21.1 18.4 23.7 21.4 17.4 *** NS NSC18:1(n-9) 19.3 20.9 22.4 18.8 20.2 23.1 *** NS NSC18:2(n-6) 1.60 1.63 1.57 1.64 1.54 1.69 NS NS NSC18:3(n-3) 1.37 1.78 1.86 1.42 1.69 2.05 *** NS NSConjugated C18:2 0.86 1.03 1.62 0.91 1.05 1.60 *** NS NS

NS not significant, *** P<0.001.

There was no overall significant effect of pasteurisation on the milk fatty acid composition with the exception of C18:2(n-6) which was significantly decreased. The results of the scores from the taste panels were inconclusive and showed no clear effect of the treatments on the overall acceptability of the milk.

It was concluded that the fatty acid composition of milk can be manipulated by dietary means to increase the potentially beneficial supply of -linolenic and conjugated linoleic acids, and total MUFAs and PUFAs to the human diet. Fatty acids, which are potentially harmful to human health, including myristic and palmitic acids can also be reduced through manipulation of the diet fed to dairy cows. Although substantial amounts of dietary -linolenic acid can be incorporated into milk from protected linseed sources, the present study suggests an incomplete protection of the oil in the treated linseed supplement. Therefore, further research on this topic is needed before the manipulation process can be optimised. The lipid supplement did not lead to an increase in either EPA or DHA in milk lipid. This result highlights the difficulty of reliably increasing the supply of -linolenic acid, which escapes biohydrogenation to be used as a precursor for EPA and DHA synthesis in vivo. The effects on fatty acid composition were not influenced to any degree by vitamin E supplementation although it did increase milk vitamin E concentrations.

3. Increase levels of C18:1

In recent decades human dietary guidelines have proposed reductions in total fat and in saturated fatty acid consumption as a means of reducing the prevalence of coronary heart disease (CHD). Many guidelines have recommended that saturated fatty acids should provide no more than 10% of dietary energy (e.g. FAO/WHO,1998). In addition, much attention has been recently paid to the beneficial effects of dietary n-3 polyunsaturated fatty acids (PUFA), not only in relation to CHD but also for the immune system and inflammatory responses (DOH, 1994).

Although there is considerable agreement on the adverse effects of the major saturated fatty acids on blood cholesterol concentrations, attempts to reduce consumption of saturated fats has been relatively unsuccessful because of resistance to low fat diets (Williams, 2000). Consequently, there has been speculation about the possibility of displacing dietary saturated fatty acids with PUFA or monounsaturated fatty acids (MUFA).

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Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Although the cholesterol-lowering effects of PUFA are greater than that of MUFA (Williams, 2000), the potential for reducing saturated fatty acids through substitution with MUFA has increased as a result of the increased ability to manipulate the fatty acid composition of meat and milk (e.g. Chilliard et al., 2000). Dairy products produced using this approach have been shown to reduce successfully blood cholesterol levels in human subjects (Noakes et al., 1996).

Free radicals are highly reactive molecules which are generated during many metabolic processes and are associated with damage to cell membranes. There is increasing interest in the role of free radicals in the aetiology of a number of serious medical conditions, including CHD, thrombosis and some cancers (e.g. Riemersma et al., 1991; National Heart Forum, 1997). An important link between free radical mediated cell damage and coronary heart disease is thought to be through oxidative damage of the PUFA in low density lipoprotein (LDL) cholesterol (Riemersma et al., 1991). Vitamin E is one of the most powerful antioxidants and can prevent the damaging effects of free radicals, most important being the prevention of lipid oxidation in cell membranes. Recent work (Cheli et al., 1995) showed a two fold increase in the concentration of vitamin E in milk when 5g all-rac- tocopheryl acetate d-1 was fed to dairy cows. The role of vitamin E in promoting medically desirable changes to the fatty acid composition of milk is however unclear.

The aim of the present study was to investigate the response to feeding to dairy cows increasing quantities of whole rapeseed, rich in oleic acid (C18:1, n-9), on the MUFA and saturated fatty acid concentrations of milk fat. In addition, the effects of dietary supplementation with vitamin E on the vitamin E and fatty acid composition of the milk were also examined. The effect of supplementary vitamin E on the oxidative stability and taste of the milk was also studied.

In a 3 x 3 factorial design, level of inclusion of whole cracked rapeseed (0, 134 and 270g lipid supplement/kg diet DM, ZR, MR or HR respectively) was investigated with three levels of additional vitamin E (Lutavit E 50, BASF) (0, 2 and 4 g/cow/d, ZE, ME or HE respectively) fed to 90 Holstein cows for eight weeks in mid-lactation. There were 10 cows per treatment. Total mixed rations consisted of a fixed level of maize and grass silage (7.5 and 2.5 kg DM respectively), various amounts of ground wheat, sugar beet feed, soya bean meal and rapeseed meal plus either 0 kg DM, 2.33 kg DM or 4.65 kg DM of whole cracked rapeseed and either 0, 2 or 4g vitamin E. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 25 litres and no weight loss (AFRC, 1993). Data were analysed using repeat measures ANOVA.

Animal performance results are presented in Table 11 and milk fatty acid composition in Table 12 for the rapeseed treatments only, as there was no significant effect of vitamin E supplementation on any of the parameters reported. Feeding increasing levels of treated rapeseed significantly decreased DM intake, milk yield and milk fat content and this decline was linear for the duration of the experiment. There were no significant interactions between level of lipid supplement and vitamin E for the aforementioned parameters. There was a significant increase in the C18 unsaturated fatty acids and decrease in C14:0 and C16:0 in the milk fat with increasing inclusion of the lipid supplement, but no effect of vitamin E supplementation. Pasteurisation led to small but significant decrease in the concentration of 18:1(n-7) (P<0.05) (2.2 to 2.0 g/100g fat).

Increasing intakes of whole rapeseeds increased (P<0.05) milk vitamin E concentration although there was little effect between MR and HR treatments. Increasing dietary intake of vitamin E linearly (P<0.01) increased milk vitamin E concentration by a factor of 1.3 between treatments ZE and HE. There were no interaction between intake of whole rapeseed and vitamin E.

Table 11 Mean dry matter intake, milk yield and milk protein and fat content on diets ZR, MR and HR.

Treatment P for effect of:

ZR MR HR Level of WR1 Linearity

over time

Animal performance

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Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Dry matter intake (kg day-1) 20.6 18.9 15.2 *** ***

Milk yield (kg day-1) 22.9 19.3 13.2 *** ***

Milk composition (g kg-1)

Fat 42.1 33.5 33.4 *** ***

Protein 36.1 37.9 38.4 NS2 NS1 Whole rapeseed, 2 Not significant, *** P<0.001

Table 12 Mean milk fatty acid composition data on diets ZR, MR and HR (g 100g-1 fat)

Treatment P for effect of:Fatty acid ZR MR HR Level of WR1 WR x

vitamin EC14:0 11.6 7.85 6.00 *** NS

C16:0 30.7 19.8 18.0 *** NS

C18:0 8.30 14.1 15.8 *** NS

C18:1 (n-9) 18.1 34.7 39.3 *** NS

C18:1 (n-7) 1.97 2.58 2.03 *** NS

C18:2 (n-6) 2.08 2.37 2.76 *** NS

C18:2 (conjugated) 0.60 1.02 0.74 *** NS

C18:3 (n-3) 0.45 0.48 0.60 *** NS1 Whole rapeseed, 2 Not significant, *** P<0.001

Supplementing dairy cows with up to 2kg d-1 of rape oil as whole cracked rapeseed resulted in significantly more C18:1 in milk fat, to over 400 g kg-1 of total milk fatty acids. Concentrations of C18:0, C18:2 and C18:3 were also increased, but by a much lesser degree and the saturated fatty acids C4:0 to C16:0 decreased substantially. These effects were not influenced to any degree by vitamin E supplementation although this did increase milk vitamin E concentrations. Thus substantial changes in milk fat composition with potentially beneficial effects on human health were achieved and without any adverse effects on milk taste. However, these improvements must be offset against the decline in milk yield and milk fat concentration which would not be commercially sustainable unless a considerable premium was paid for this modified milk. Alternatively, processing methods must be found to protect the rumen from the negative effects of rape oil in the whole cracked rape on fibre degradation, so that the changes in milk fatty acid composition can be achieved without the reduction in animal performance.

4. Increase levels of vitamin E

Study 1 - Review the metabolism of vitamin E in the body

There are several forms of vitamin E (tocopherol) of which -tocopherol is the most biologically active and widely distributed. However synthetically produced -tocopherol has only 74 % potency compared with the natural compound (Bender, 1992). The vitamin E content of feedstuffs is highly variable with fresh forages containing substantial amounts but these are reduced when the forage is dried. The side chain of tocopherol has three centres of asymmetry, which can have either the R or S configuration, resulting in eight (23) possible isomers. The naturally occurring compound has the R-configuration on all 3 centres of asymmetry and is called RRR--tocopherol (also known as d--tocopherol). The international standard of vitamin E activity is based on a mixture of all 8 isomers (all racemic) of synthetically produced -tocopheryl acetate i.e. 1 international unit ( IU) = 1 mg of all-rac--tocopheryl acetate.

The fate of vitamin E in the rumen remains uncertain. Early work showed that vitamin E was degraded in the rumen and the extent was related to the cereal content of the diet. However, recent work suggests that virtually all

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Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

vitamin E passes into the intestines unchanged. Vitamin E absorption occurs mainly in the small intestines and is associated with fat digestion. In humans, vitamin E absorption is enhanced by the presence of medium-chain triglycerides and inhibited by poly-unsaturated fatty acids. Once vitamin E has been absorbed, it is transported in the blood by various lipoproteins including chylomicrons, high, low and very low density lipoproteins (HDL, LDL and VLDL). Similar mechanisms are thought to operate in the ruminant.

Vitamin E is not stored in the body for release to any deficient cells/tissues/organs, instead it is widely distributed in cell membranes where it is available for local utilisation. There is no specific mechanism for vitamin E uptake by tissue but there are 2 indirect mechanisms. Firstly, lipoprotein lipase releases the vitamin by hydrolysing the triglycerides in chylomicrons and VLDL. Secondly, LDL bound vitamin E is actively taken up within LDL by means of LDL receptors. The retention of vitamin E in tissue depends on the presence of binding proteins. The mammary gland extracts a large percentage of fatty acids from plasma LDL and chylomicrons for milk fat synthesis. This suggests that vitamin E uptake by the mammary gland is similar to other tissues but on a larger scale.

Vitamin E is the first line of defence against oxidation of polyunsaturated fatty acids contained in cell membranes by free-radical chain reactions. Vitamin E can be recycled by reacting with vitamin C or excreted in bile by the eventual formation of quinone and hydroquinone. Other suggested functions of vitamin E include prostaglandin formation, DNA and protein synthesis as a component of the electron chain in mitochondria and stimulating the immune system suggesting a role in the nervous system. Vitamin E may also have a specific physio-chemical role in maintaining membrane structure.

While vitamin E is mainly excreted via bile in the faeces, there are also two minor routes of excretion via urine and skin. The -tocopherol content of milk and colostrum is typically quoted as 0.3 and 1.9 g -tocopherol /ml milk respectively, but has been shown to vary five fold during lactation, which may reflect seasonal changes in vitamin E intake, milk fat content and the efficiency of transfer across the mammary gland.

Based on the literature study several shortfuls in our understanding of the parameters affecting vitamin E uptake and metabolism were identified. Threfore, It is recommended that further research is required on the following topics:a) The extent to which vitamin E is degraded in the rumen and whether this varies with raw material (especially

with cereal grains) should be resolved.

b) The form in which vitamin E is provided influences the supply of biologically active tocopherol to the tissues. Consequently, it is recommended that all experimental reports clearly state the form of vitamin E used and the supply in international units.

c) There is very little information in the literature regarding the uptake mechanism from blood to the mammary gland or the processes involved in the incorporation of vitamin E into milk. More work should be done to investigate the overall efficiency of vitamin E transfer into milk and the factors that can affect this.

d) The extent to which vitamin E can protect milk fat from the process of lipid peroxidation and the nature of the interaction between increasing levels of vitamin E in milk and polyunsaturated fatty acids on this process requires further investigation.

Study 2

The review reported in Study 1 highlighted the gap in the knowledge regarding the extent to which vitamin E is degraded in the rumen. This study set out firstly to investigate the effect of replacing a standard dietary vitamin E supplement with two rumen-protected vitamin E products on milk vitamin E content. Secondly having found a source of vitamin E with reduced rumen degradation to do a dose-response study and investigate the response in concentration of vitamin E in milk.

In a randomised block design a standard diet supplemented with four different sources of vitamin E (Control, Lutavit E50, BASF 2g/d ; T1 Rumen protected, Balchem Co. 2g/d ; T2 and T3 Rumen protected, Aventis Ltd. at 2 and 4 g/d respectively) were fed to 48 cows for eight weeks in mid-lactation. There were 12 cows per treatment. Total mixed rations consisted of a fixed level of maize and grass silage (8.6 and 2.9 kg DM

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Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

respectively), various amounts of ground wheat, sugar beet feed, soya bean meal and rapeseed meal were added. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 35 litres and no weight loss (AFRC, 1993). Data were analysed using repeat measures ANOVA.

Animal performance results are presented in Table 13, along with vitamin E intake and output in milk. There was no significant effect of vitamin E source on DM intake, milk yield or milk fat content. There were no significant differences between the Control and either T1 or T2 in the calculated intake of vitamin E. However, as expected, T3 had a significantly greater vitamin E intake than T2 due to the higher inclusion rate in the diet. There was no significant difference between treatments for vitamin E output but there was a significantly lower transfer efficiency for T3 compared with T2.

The maximum concentration of vitamin E in milk was 1.7 mg kg-1, which is nearly double the amount reported in the UK composition of foods tables for average winter production of whole milk. In this experiment, the maximum concentration of vitamin E in milk fat was 46 g g-1 milk fat, which is the same as values reported in the previous studies (44 - 47 g g-1 milk fat). This may suggest an upper physiological limit for the secretion of vitamin E in bovine milk fat. There was no statistically significant effect of feeding rumen protected vitamin E on milk vitamin E concentration. Increasing the intake of vitamin E by increasing the inclusion of rumen-protected vitamin E tended to increase milk vitamin E content but the efficiency of transfer was low, particularly at high rates of vitamin E supplementation, and only 0.47 % of the additional vitamin E was secreted in milk. Both published work and previous research done at ADAS Bridgets have shown that less than 1% of additional vitamin E was secreted in milk when administered in the synthetic form.

Table 13 Dry matter intake, milk yield and milk protein and fat content, vitamin E intake and milk output (expressed as all-rac--tocopheryl acetate, mg/d) on diets Control, T1, T2 and T3.

Treatment s.e. P

value

C T1 T2 T3

Animal performance

Dry matter intake (kg day-1) 23.8 23.8 23.3 23.3 0.30 NS

Milk yield (kg day-1) 32.8 32.6 32.1 31.2 0.47 NS

Milk composition (g kg-1)

Fat 38.8 34.7 35.7 36.3 0.19 NS

Protein 34.4 34.7 34.3 34.4 0.029 NS

Vitamin E intake (mg d-1) 2526 2533 2519 4515 13.2 ***

Milk vitamin E composition (mg kg-1) 1.6 1.3 1.4 1.7 0.11 NS

Milk vitamin E output (mg d-1) 46.6 46.0 45.9 55.3 3.55 NS

Transfer efficiency into milk (%) 1.8 1.8 1.8 1.2 0.11 ***

NS, not significant, *** P<0.001

One explanation for the poor transfer efficiency of dietary vitamin E into milk is that neither of these samples of rumen-protected vitamin E actually resisted ruminal hydrolysis. Since there was no direct measurement of rumen degradation of dietary vitamin E in this study, this cannot be confirmed. However, in vitro studies elsewhere (Leedle et al., 1993; Weiss et al., 1995) have suggested that standard vitamin E may not be degraded in the rumen. Other explanations for the poor transfer of vitamin E to milk include: poor absorption of vitamin E in the lower gut; low uptake of vitamin E from blood by the mammary gland; form of vitamin E (natural versus synthetic).

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Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

This study has confirmed that the transfer of dietary vitamin E into milk is variable, and that further studies are necessary to determine fully those factors limiting the secretion of vitamin E into milk and to identify the potential to further enhance the vitamin E content of bovine milk.

5. Increase concentrations of selenium

Study 1 - Review dietary sources, levels and methods of analysis for selenium

Selenium is an essential nutrient. It is a component of a number of glutathione peroxidases, which are responsible for detoxifying peroxides (“free radicals”) produced as by-products of the body’s normal metabolic processes but which are highly toxic when present in excess amounts. Recent research and epidemiological studies have indicated that increased selenium intakes may be associated with reduced cancer risk, while deficiency has been linked to impaired thyroid hormone function, reduced levels of reproduction, the virulence of some viral infections (including AIDS) and brain function. In addition, there is evidence that increasing the selenium intake by dairy cows may have health and welfare benefits particularly in terms of reduced somatic cell counts.

Daily intake of selenium in the UK has declined steadily over a number of years and is now below levels considered by a number of authorities as necessary to maintain optimum enzyme function. The decline is attributed to a reduction in the use of Canadian wheat in preference for UK wheat. The selenium content of UK wheat is about one third that of Canadian wheat. As a result, health professionals and policy makers are investigating alternative methods of increasing selenium intake by increasing concentrations in staple foods.

The selenium concentration in bovine milk in the UK is ~10 µg litre -1, and reflects selenium intake by dairy cows. The UK Feedingstuffs Regulations (implementing an EC Directive) restricts the amount of selenium that can be added to diets of dairy cows. Evidence from the UK animal feed industry suggests that most compound feeds for dairy cows are supplemented with selenium to a level close to the maximum permitted by legislation. Most of the supplementary selenium is in the inorganic form. Therefore, it appears that there is little scope to increase milk selenium concentration using present methods of supplementation. Because of concerns regarding environmental pollution with selenium, any increase in the maximum amount of selenium permitted in dairy cow diets is unlikely.

A limited number of studies have been done which confirm that the selenium concentration of milk can be increased significantly by providing supplementary dietary selenium. However, the form of the selenium is critical, with organic selenium being more effective than inorganic forms. There appears little scope for substantially increasing milk selenium concentration by using inorganic selenium while remaining within dietary limits for dairy cows set out in the Feedingstuffs Regulations. At present, the use of organic selenium is not permitted under EU regulations. Approval would generally be granted for individual products (rather than the form of the selenium) which relies on manufacturers submitting dossiers for approval by EU Member States. There are no clear guidelines as to what the optimum selenium concentration in milk should be. Assuming no further reduction in milk intake by the human population, a two-fold increase in milk selenium concentration from current levels would mean that milk and milk products provided ~10% of estimated daily requirements of adults in the human population.

Research is needed to confirm whether significant increases in milk selenium concentration can be achieved, under UK conditions, by using organic forms of selenium while remaining within the limits imposed by current legislation. If this cannot be achieved, then studies should be undertaken to demonstrate that the use of organic selenium at levels above those currently permitted by legislation result in no increase in selenium excreted in faeces and urine. This evidence could then be used to apply to the European Commission for a derogation on the maximum permitted level of selenium in dairy cow diets where the selenium is given in an organic form. Further research is also needed to confirm that there are no adverse effects on metabolism, health or reproduction from long-term supplementation with organic selenium.

Study 2

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Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

The review reported in Study 1 highlighted the gap in the knowledge regarding the dietary source and inclusion rate of selenium concerning increasing the concentration of selenium in milk. This study set out to investigate this.

In a 3 x 3 factorial design a standard diet was supplemented at three dietary selenium concentrations (L, M and H, 0.38, 0.76 and 1.14 mg/kg DM respectively) from three selenium sources (S, Y and C, sodium selenite, selenium yeast and selenium-amino acid chelate respectively) to 90 mid-lactation dairy cows (10 per treatment) for eight weeks. Total mixed rations consisted of a fixed level of maize and grass silage (8.4 and 2.8 kg DM respectively), various amounts of ground wheat, sugar beet feed, soya bean meal and rapeseed meal were added. Diets were formulated to supply sufficient metabolisable energy and protein for maintenance + 30 litres and no weight loss (AFRC, 1993). Data were analysed using repeat measures ANOVA.

Animal performance results are presented in Table 14, along with selenium intake in milk. There was a significant source x level of Se interaction for DM intake (P<0.05) with Se selenite decreasing DM intake and the level of the other two sources having no effect on DM intake. Cows fed the selenium yeast (Y) had a greater response in milk selenium concentration and output (+1.6 mg/d and +68g/litre respectively) to increasing dietary concentration of selenium compared with cows fed the other two sources (S and C) (+7 and +17 mg/d and +4 and +6 g/litre for milk selenium output and concentration respectively). Milk yield was significantly (P<0.01) suppressed with increasing inclusion of selenium (28.7, 26.7 27.8 l/cow/d for low, medium and high Se respectively) though there was no significant effect of source of Se. There was no significant effect of selenium source or level on milk fat or protein content.

Table 14 Dry matter intake, milk protein and fat content, selenium intake on diets supplemented with different sources and levels of selenium.

Treatment Dry matter intake (kg/d)

Selenium intake (mg/d)

Milk selenium content (g/l)

Milk fat (g/kg total fat)

Milk protein (g/kg total protein)

LS 21.6 9.4 13.6 40.4 34.8MS 19.5 12.6 15.9 42.9 35.6HS 20.4 15.8 18.2 41.0 34.9LY 20.8 8.5 28.4 40.7 34.9MY 20.8 15.3 68.2 41.2 35.1HY 20.5 22.1 96.6 44.8 35.2LC 19.9 10.3 13.6 40.7 35.1MC 20.2 15.6 13.6 40.8 35.6HC 20.5 19.8 20.5 40.3 34.9

s.e. 0.41 0.03 1.37 0.31P value Source NS *** *** NS NSLevel NS *** *** NS NSSourcexlevel * *** *** NS NS

NS not significant, * P<0.05, *** P<0.001.In this experiment, increasing the selenium concentration of the diet led to increases in milk selenium concentration for all three dietary sources. However, this response was substantially greater for the selenium yeast resulting in the maximum milk selenium concentration being nearly ten times greater than that found in average UK whole milk. This was associated with an increase in the transfer efficiency from the diet into milk. There are no current guidelines to what the optimum concentration in milk should be but a concentration of 20 g/litre has been suggested in Finland. In this experiment, this concentration was only achieved when feeding the selenium yeast. However, the use of selenium yeast in livestock feeds is currently not authorised within the EU.

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Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Although the evidence for the effect of organic selenium on the selenium concentration of milk appears convincing, it is based on relatively few experiments involving lactating dairy cows. Further studies are required to confirm these effects under UK conditions and develop response curves to different levels of supplementation to achieve target milk selenium concentrations whilst remaining within permitted EU dietary concentrations. The effect of long-term selenium supplementation on its concentration in cows’ milk is currently unknown. Further work is therefore required to determine whether increasing milk selenium concentration is sustainable over a whole lactation. In addition, the long-term effects on dairy cow health, fertility and performance should be investigated. In this experiment there were significant but inconsistent effects of selenium supplementation on milk yield. Further work is required to clarify fully this effect.

6. Increase levels of natural antioxidants

Objective 6 not achieved, as agreed with the MAFF project officer Dr David Garwes.

7. Use the data from Objectives 1, 2 and 3 to test against the model published by Hermansen (1995)

Despite the increasing importance of individual fatty acids from cows' milk in the human diet, there have been few attempts to derive quantitative models which can predict milk fatty acid composition from the dietary fatty acids consumed. The purpose of this study was to test recently published models (Hermensen, 1995) using a large data set derived from the studies reported above. A further objective was to examine the possibility that improved relationships between dietary and milk fatty acids may be possible.

Dietary and milk fatty acid data were extracted from 10 studies carried out at ADAS Bridgets comprising of a total of 73 dietary treatments with a wide range of fat sources. It was concluded that the models published by Hermensen (1995) are not satisfactory predictors of the concentrations of milk fatty acids C12 to C18 in the data from recent ADAS studies. Some of this may be due to differences in the fatty acid make up of the two populations of diets and the fact that some at least partially protected fats were included. Improved models were derived from the present data but the associated errors were higher than optimum.

However, the findings suggest that with a wider range of dietary fatty acids and other variables, together with the development of more complex models, much improved prediction models may be possible. These must also be able to predict the milk fatty acids of crucial importance to human health, which were not included in the present study.

References

AFRC, 1993. Energy and Protein Requirements of Ruminants. Pub. CAB International, Wallingford

Alderson, N.E., Mitchell, G.E., Little, C.O., Warner, R.E. and Tucker, R.E., 1971. Preintestinal disappearance of vitamin E in ruminants. Journal of Nutrition 101:655-660.

Allison, R.D., 2000. Dietary strategies to increase the levels of oleic acid (C18:1) fatty acids in cows milk. MAFF ROAME No. LS1803.

Allison, R.D and Laven, R., 2000. The effect of vitamin E supplementation on the health and productivity of the dairy cow: a review. Veterinary Record, In press.

Bender, D. A., 1992. Nutritional Biochemistry of the Vitamins, Chapter 4: Vitamin E tocopherols and tocotrienols, Cambridge University Press, Cambridge, UK. pp 87-105.

Cheli, F., Baldi, A., Bontempo, V., Cattaneo, D. and Fabbri, B., 1995. Effect Of Vitamin E Administration On Milk And Plasma - Tocopherol Levels In Dairy Cows. Proceedings of the 45th Annual Meeting of the EAAP.

Chilliard, Y., Ferlay, A., Mansbridge, R.M., Doreau, M., 2000. Ruminant milk plasticity: nutritional control of saturated, polyunsaturated, trans and conjugated fatty acids. Annales de Zootechnie 49:181-206

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MAFFproject code

LS1803

Department of Health, 1994. Nutritional aspects of cardiovascular disease. Report on Health and Social Subjects. 46. London : HMSO.

FAO/WHO, 1998. General conclusions and recommendations of the consultation, In: Expert Consultation on Fats and Oils in Human Nutrition, Food and Agriculture Organisation of The United Nations, FAO/WHO, Rome.

Gulati, S.k., Byers, E.B., Byers, Y.G., Ashes, J.R. and Scott, T.W., 1997. Effect Of Feeding Different Fat Supplements On The Fatty Acid Composition Of Goats Milk. Animal Feed Science and Technology, 66:159-164

Hebeisen, D.F., Hoeflin, F., Reusch, H.P., Junker, E. and Lauterburg, B.H., 1993. Increased concentrations of Omega-3 fatty acids in milk and platelet rich plasma on grass-fed cows. International Journal for Vitamin and Nutrition Research 63: 229-233.

Herdt, T.H. and Stowe, H.D., 1991. Fat soluble vitamin nutrition for dairy cattle. Veterinary Clinics of North America: Food Animal Practice 7:391-416.

Hermansen, J.E., 1995. Prediction Of Milk Fatty Acid Profile In Dairy Cows Fed Dietary Fat Differing In Fatty Acid Composition. Journal of Dairy Science 78:872-879.

Leedle, R.A., Leedle, J.A.Z. and Butine, M.D., 1993. Vitamin E is not degraded by ruminal microorganisms: Assessment with ruminal contents from a steer fed a high concentrate diet. Journal of Animal Science 79:2568-2573

Lundin, P.K. and Palmquist, D.L., 1983. Vitamin E supplementation of high fat diets for dairy cows. Journal of Dairy Science, 66:1909.

Mansbridge R.J., 1997. To determine the effect of feeding high levels of fish oil and additional and vitamin E on the fatty acid composition and shelf life of bovine milk. MAFF ROAME No. MS1805.

Mansbridge R.J., 1999. Dietary strategies to increase the levels of -linoleic fatty acid (C18:3) in cows milk. MAFF ROAME No. LS1803

McCance, R.A. and Widdowson, E.M., 1998. Fatty Acids. Seventh supplement to the 5th Edition of The Composition of Foods. The Royal Society of Chemistry and MAFF. 209pp

Mpelimpasakes, N.G., 1981. Effect of various rations on fatty acid composition of bovine milk fat. Ellenike Kteniatrike 24: 81-93

National Heart Forum: Preventing Coronary Heart Disease, 1997. The role of antioxidants, vegetables and fruit. Eds L. Rogers and I Sharp. HMSO.

Noakes, M., Nestel, P.J. and Clifton P.M., 1996. Modifying the fatty acid profile of dairy products through feedlot technology lowers plasma cholesterol of humans consuming the products. American Journal of Clinical Nutrition, 63, 42-6.

Riemersma, R.A., Wood, D.A., Macintyre, C.C., Elton, R.A., Gey, K.F., Oliver, M.F., 1991. Antioxidants and pro-oxidants in coronary heart disease. Lancet, 337: 1-5

Scollan, N.D., Fisher, W.J., Davies, D.W.R., Fisher, A.V., Enser, M. and Wood, J.D., 1997. Manipulating the fatty acid composition of muscle in beef cattle. Proceedings of the British Society of Animal Science 1997, 22

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Projecttitle

Dietary strategies to enhance the fatty acid composition of milk     

MAFFproject code

LS1803

Weiss, W.P., Smith, K.L., Hogan, J.S. and Steiner, T.E., 1995. Effect of forage to concentrate ratio on disappearance of vitamins A and E during in vitro ruminal fermentation. Journal of Dairy Science 78:1837-1842.

Williams, C.M., 2000. Dietary fatty acids and human health. Annales de Zootechnie 49:161-292

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