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Summary

Eric KolverDairying Research CorporationHamilton

Nutrition GuidelinesFor The HighProducing DairyCow

n The priorities when feedingsupplements are first to get theappropriate farm system in place thatwill make profits from supplements,and second to consider feed type andmix of feeds.

n The amount of supplementary feed tobe used will be determined by the feeddeficits in the farm system.

n The type of supplementary feedrequired will be determined byprofitability, by the amount ofsupplementary feed being used, andby the nutrients first-limiting milksolidsproduction.

n Nutritional guidelines can be used tomeet the nutritional requirements of thehigh producing dairy cow and to avoidhealth problems.

n The New Zealand dairy cow has a largepotential to grow and producemilksolids when fed well.

Introduction

Successful dairying systems in New Zealandgrow grass and efficiently convert this grass intomilk and money. For those farmers that do thiswell, what is the next step? For many, the onlyoptions are to get bigger or more intensive. The

profitability of the intensification option will dependon how well supplemental feed can beincorporated into the pasture system.

A cow has clear nutrient requirements toproduce certain levels of milksolids, and many ofthe principles used in intensive diets overseascan be applied in New Zealand, with somemodification for fresh pasture diets.

This paper will discuss the farm system withinwhich supplementary feed can be profitable, howto decide what mix of feeds to use, and the useof feeding guidelines to develop pasture-basedrations for high producing dairy cows.

Get the System Right

Most of the extra profit gained from feedingsupplements will be achieved by getting thecorrect farm system in place. When this is done,feed combinations can be incorporated into thesystem. The principles of how best to usesupplements in a pasture-based system areknown, and have been discussed at RuakuraFarmers’ Conferences (Kidd, 2000; Macdonald,1999; Penno 1998; Van der Poel, 1996). Theseprinciples were demonstrated in the 1.75t MS/hafarm systems experiment at DRC No. 2 Dairy inwhich extra feed inputs in the form of maize grain,maize silage, or a balanced ration wereincorporated into a highly stocked pasturesystem (Table 1). While pasture growth curveson individual farms throughout New Zealand maybe different to DRC No. 2 Dairy, the principles ofthis farm system can be broadly applied. Theseprinciples are:

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1. Increased cow milking days: High per cow andper ha milksolids production is achieved by usingsupplements to increase cow milking days by firstextending lactation through earlier calving ormilking more cows longer, and second byallowing a higher stocking rate.

2. Increased stocking rate: Once pasture andextra feed are being efficiently utilised, the farmeffectively becomes a milking platform onto whichmore feed can be brought and more cows milked.

3. Fill true feed deficits: Supplementary feeds willdecrease profitability if used when adequatepasture is available. Therefore profits are madewhen supplements are used to fill true feeddeficits, which result from the higher stocking rateand the extended lactation. How do we decidewhen to supplement the milking cows? Decisionrules developed from the 1.75t/ha research at No.2 Dairy are used to supplement high stockedsystems when:• Intake falls below targeted intakes of 15-16 kg

DM/cow/day (early lactation)• Intake falls below 12 kg DM/cow/day (late

lactation).

4. Feed energy: Energy is the key driver of milkproduction. Every kg of DM put into the DRC No.2 Dairy farm system produced 78-99 g MS(immediate and carryover response). Thisresulted in the supplemented cows producing 363to 407 kg MS/cow compared with 269 kg MS/cow(Table 1). The balanced ration resulted in a 10%increase in milksolids production compared withthe maize grain diet during summer. But thisdifference made little impact on total milksolidsproduction per cow over the year. This milksolidsresponse indicates that while imbalances in thepasture and maize grain diet existed duringsummer, this ration was reasonably balanced for

much of the year. When expressed on an energybasis, the maize grain, maize silage, andbalanced ration all gave a similar annual responseof 7.5 g MS/MJ ME.

5. Cost structure: The profitability of thesesystems will depend on the price of thesupplementary feed and the labour and capitalcost structures associated with this system.These have been described for the 1.75t MS/haexperiment (Macdonald, 1999).

Table 1: Milksolids response to supplements for four farmlet herds stocked at 4.42 cows/ha inthe 1.75t MS/ha trial at DRC No 2 Dairy (for details and EFS see Macdonald 1999).

Herd

Control Maize grain Maize silage Balanced

Milksolids, kg/cow 269 400 363 407Milksolids, kg/ha 1190 1768 1606 1800Supplement, kg DM/cow 68 1395 1279 1458Response, g MS/kg DM fed 99 78 99

Get the Feed Right

Once the system is in place, the type ofsupplement used becomes the next priority. Asa general rule, if less than 25-30% of the diet isprovided by supplementary feed, the main priorityis to ensure that the supplement provides highquality energy. Exceptions to this rule are rapidlydigested carbohydrates, e.g. molasses, whichhave maximum recommended feeding levelsconsiderably less than 25% of the ration. Whenthe farm system has large feed deficits thatrequire more than 30% of the diet to be fed assupplements, using the right type or mix of feedscan become important to avoid nutrientimbalances and health problems such asacidosis and laminitis.

Table 2 lists the nutrient content of commonlyavailable energy, fibre, and protein feeds, and lessconventional feeds. Macro mineral sources suchas calcium (limeflour), phosphorus (dicalciumphosphate), salt (agsalt), and magnesium(causmag) are also available. Sourcing cheapfeed is an exercise in negotiation and creativethinking to maintain quantity and consistency offeed supply, especially for large herds.

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Table 2: Nutrient composition of supplementary feeds.

DM ME CP BP Sol CP NDF eNDF SC Starch Fat Ash Ca P Mg K S Na Cl

(%) (MJME/kg) (%) (%CP) (%CP) (%) (%NDF) (%) (%SC) (%) (%) (%) (%) (%) (%) (%) (%) (%)

PASTURE

Pasture, spring 12-18 11-12.5 18-35 20-30 25-50 35-45 40 7-25 2-4 3-6 10-12 0.2-1.5 0.2-0.6 0.1-0.4 1.5-4.5 0.1-0.6 0.03-0.6 0.1-1.5

Pasture, summer 15-20 9.5-10.5 14-22 25-35 20-35 42-52 50 7-25 4-8 3-5 10-12 0.2-1.5 0.2-0.6 0.1-0.4 1.5-4.5 0.1-0.6 0.03-0.6 0.1-1.5

Pasture, summer dry 20-30 8-9.5 9-14 35-45 15-25 52-65 100 7-15 4-8 2-4 8-10 0.2-1.5 0.2-0.6 0.1-0.4 1.5-4.5 0.1-0.6 0.03-0.6 0.1-1.5

SILAGE

Pasture, good 23 10.0 17.0 22 52 45 90 22.0 7 3.0 10.0 0.80 0.30 0.21 2.30 0.24 0.10 0.20

Pasture, poor 38 9.0 15.0 29 44 55 90 15.0 8 3.1 9.5 0.55 0.28 0.14 2.0 0.20 0.16 0.19

Barley 33 9.8 11.9 15 70 57 65 19.9 100 2.9 8.3 0.52 0.29 0.19 2.57 0.24 0.12 0.00

Lucerne 20 9.5 20.0 23 54 51 82 16.7 45 3.5 9.5 1.29 0.29 0.25 2.84 0.29 0.05 0.34

Maize 33 10.3 8.0 31 48 49 80 35.1 100 3.1 4.0 0.25 0.23 0.18 1.20 0.13 0.01 0.00

Pea 33 8.8 13.1 22 63 59 61 18.3 100 3.3 9.0 0.87 0.34 0.23 3.08 0.25 - -

Wheat/Oat 36 10.5 13.0 24 67 59 61 16.1 100 3.6 8.3 0.57 0.32 0.20 2.85 0.25 0.07 0.07

HAY

Pasture, good 85 9.7 17.0 31 31 54 100 17.7 44 2.6 9.0 0.80 0.40 0.20 2.32 0.26 0.20 0.62

Pasture, poor 85 7.3 7.0 37 29 66 100 14.6 45 2.6 6.3 0.40 0.30 0.18 1.67 0.20 0.15 0.60

Barley straw 87 6.5 4.3 76 20 80 100 6.7 100 1.9 7.1 0.30 0.07 0.23 2.37 0.17 0.14 0.67

Pea straw 85 6.7 6.3 - - - - - - - - 1.60 0.12 - - - - -

Wheat straw 89 6.3 3.6 76 20 79 100 7.8 100 1.8 7.8 0.18 0.05 0.12 1.42 0.19 0.14 0.32

CONCENTRATE

Barley 89 13.0 11.0 27 31 21 34 61.4 90 2.0 2.8 0.06 0.44 0.18 0.57 0.17 0.03 0.18

Bran (wheat) 89 9.8 17.1 29 42 51 19 20.6 95 4.4 6.9 0.13 1.31 0.60 1.50 0.25 0.04 0.05

Lupin 89 12.0 34.2 32 26 33 23 22.0 90 5.5 5.1 0.26 0.44 0.00 0.91 0.00 0.00 0.00

Maize grain 89 13.6 8.0 52 12 9 5 75.1 99 4.3 1.6 0.02 0.31 0.12 0.40 0.12 0.003 0.05

Meat & bone meal 94 10.7 54.0 49 15 0 0 4.0 0 10.4 31.5 9.50 4.7 0.25 0.49 0.45 0.70 0.30

Oats 89 11.5 13.0 17 27 31 34 47.5 90 4.9 3.6 0.10 0.41 0.15 0.53 0.19 0.01 0.11

Peas 87 13.0 24.0 - - 23 - 46.2 - 1.8 5.0 0.14 0.43 0.17 1.80 - 0.01 -

Soya bean 90 12.9 50.0 35 20 14 23 27.3 90 1.4 7.3 0.30 0.68 0.30 2.12 0.37 0.01 0.08

Wheat 89 12.6 11.3 24 23 14 3 70.2 90 1.9 2.6 0.07 0.36 0.13 0.46 0.16 0.01 0.08

Whole cotton seed 88 16.0 23.0 41 27 44 100 3.7 90 18.0 4.5 0.16 0.60 0.37 1.20 0.26 0.01 -

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Table 2: Nutrient composition of supplementary feeds (cont'd from previous page).

DM ME CP BP Sol CP NDF eNDF SC Starch Fat Ash Ca P Mg K S Na Cl

(%) (MJME/kg) (%) (%CP) (%CP) (%) (%NDF) (%) (%SC) (%) (%) (%) (%) (%) (%) (%) (%) (%)

BY PRODUCTS

Apple pomace 22 10.4 5.4 51 11 41 34 44.0 100 4.7 5.0 0.23 0.11 0.00 0.53 0.11 0.00 0.00

Bread 63 14.0 13.0 - - 18 - 60.3 90 5.7 3.0 0.17 0.15 0.40 0.19 - 0.80 -

Brewers grains 24 10.0 23.0 45 10 49 18 11.2 100 7.3 4.4 0.30 0.60 0.10 0.10 0.36 0.20 0.17

Cabbage 8 13.2 19.0 - - 29 0 60.4 - 3.4 9.0 0.60 0.30 0.19 3.13 - 0.23 -

Carrots 12 13.2 9.9 - - 9 0 59.4 - 1.4 8.2 0.40 0.35 0.20 2.80 0.17 1.04 0.50

Chocolate 95 19.6 12.9 20 50 4.7 0 30.4 - 48.7 3.3 0.07 0.17 0.10 0.37 0.13 0.09 -

Fishmeal 92 11.7 66.7 60 12 1.47 10 2.0 90 10.5 20.8 5.65 3.16 0.16 0.76 0.49 0.43 0.60

Molasses 75 12.0 4.0 0 95 0 0 82.8 0 0.1 13.1 1.10 0.09 0.43 3.30 0.47 0.15 3.10

Onion 10 13.0 11.6 - - 18 - 65.1 100 1.6 3.7 0.20 0.33 0.10 1.57 0.10 0.03 0.20

Pizza waste 54 17.0 21.7 - - - - - - 30.2 4.8 0.26 - - - - 1.20 -

Potato 23 13.0 10.0 - - 7.6 - 77.2 100 0.4 4.8 0.04 0.24 0.14 2.17 0.09 0.09 0.28

Pumpkin 8.4 12.9 16.0 - - 5.9 - 67.4 100 1.2 9.5 0.25 0.52 0.14 4.0 - 0.01 -

Tallow 99 31.0 0.0 0 0 0 0 0.0 0 99.0 1.0 0.57 0.06 0.06 0.32 0.00 0.01 0.00

Urea 99 0.0 281 0 0 0 0 0.0 0 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Where ME=metabolisable energy, CP=crude protein, BP=bypass protein, Sol P=soluble protein, NDF=neutral detergent fibre, eNDF=effective fibre, SC=soluble carbohydrates.Data from Fox et al., 1999; Holmes and Wilson, 1987; NRC, 1989.

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What Nutrients Limit Productionon Pasture?

To decide what feed or mix of feeds to use,consider:

• Price (cents/MJ ME).

• The proportion of the diet fed assupplementary feed (determined by the sizeof the feed deficits in the farm system).

• The targeted level of milksolids production,as different nutrients will be first-limitingmilksolids production as productionincreases.

On good quality pasture (e.g. 11.5-12 MJME/kg DM, 24-28% crude protein (CP), 38-45%neutral detergent fibre (NDF), 80% organic matter(OM) digestibility), energy will generally be thenutrient first-limiting milk production up to 25 kgmilk/cow/day (2 kg MS/cow/d) (Table 3). Thismeans that milksolids will increase if energyintake is increased, but milksolids yield is unlikelyto increase if protein or other nutrients areincreased. To produce more than 30 kg milk/cow/day (2.4 kg MS/cow/day), both protein and energyintake will need to be increased. To produce morethan 35 kg milk/cow/day (2.8 kg MS/cow/day),additional protein will be required.

Kolver and Muller (1998) studied exactly whycows grazing ad lib on good quality pastureproduced less milk than cows fed ad lib with abalanced total mixed ration (TMR). Cows thatwere fed TMR and produced 44.1 kg milk/cow/day were compared with control cows grazingall pasture and producing 29.6 kg milk/cow/day.Why did the grazing cows produce 15.4 kg less

milk than the cows fed TMR? By using a computermodel (Cornell Net Carbohydrate and ProteinSystem), this difference in milk production couldbe explained by five variables.

If the grazing cows, which had a DM intake of19 kg DM/cow/day, had the same DM intake asthe cows fed TMR (23.4 kg DM/cow/day), an extra9.4 kg of milk could have been produced (a totalof 38 kg of milk/cow/day). The energy used forgrazing and walking cost an estimated 3.7 kg ofmilk/cow/day; the energetic cost to the cow ofconverting surplus nitrogen in pasture to urea cost1.8 kg of milk/cow/day; and differences in milkcomposition and live weight accounted for therest of the difference in milk production. Thisshows that if grazing dairy cows could simply eatmore high energy pasture, potential productioncould largely be achieved by feeding a pasture-only diet.

However, there are limits to the extent that acow can increase DM intake of fresh pasture. Fora 500-kg cow, a DM intake of 18 kg of high qualitypasture could potentially produce 2 kg MS/cow/day, and a DM intake of 20 kg/cow/day couldproduce 2.3 kg MS/cow/day. Based on studiesfrom around the world with high producing dairycows grazing high quality pasture, DM intake ofhigh quality pasture seems to be limited to 19 to20 kg DM/cow/day. To achieve higher levels ofproduction (e.g. 2.9 kg MS/cow/day), a DM intakeof 24 kg DM/cow/day would be required. This ismore than the cow can achieve on pasture alone,and a significant proportion of the diet (e.g. 40%)would need to be supplementary feed to achievethis high DM intake and production level. Highquality pasture will allow high levels of milksolidsproduction, but it is likely that a diet containingmore than just pasture will be required forextremely high levels of production.

Table 3: Nutrients first-limiting milk production on high quality pasture diets.

kg milk/cow/day Nutrient first-limiting milk production

20 Energy

25 Energy

30 Energy and protein

35 Protein

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Theory and Practice of FeedingCows Well

The nutrient requirements of dairy cows havebeen well researched, and various feedingrecommendations have been developed aroundthe world. While the nutrients required to producehigh levels of milksolids will be the same for NewZealand cows as for overseas cows, our relianceon fresh pasture as a major feed means thatsome of these nutritional recommendationsrequire some adaptation for pasture-based diets.

The following discussion outlines thetheoretical nutrient requirements of the highproducing dairy cow, and how in practice theserecommendations can be applied to pasture-based diets.

EnergyTheory: Energy, expressed as mega joules ofmetabolisable energy (MJ ME/kg DM), is the keydriver of milk production. To produce one kg ofmilksolids requires 62 MJME (Jersey; 6.0%milkfat, 4.2% protein), 64 MJME (Friesian-Jerseycross; 5.0% milkfat, 3.7% protein), and 65 MJME(Friesian; 4.5% milkfat, 3.5% protein) (Table 4).

Example: A 500 kg Friesian producing 2 kg MS/day and losing 0.25 kg/day would require anenergy intake of 186 MJ ME/day:

• maintenance + milksolids - live weight loss• 64 MJ ME + (2 kg MS/d x 65 MJ ME/kg MS) -

(0.25 kg LW x 32 MJ ME/kg LW loss)

If pasture contained 11 MJ ME/kg DM, DM intakewould need to be 17 kg DM/cow/day (186 MJ MEper day/11 MJ ME per kg DM).

Practice: Use high quality feed (greater than 10.5-11 MJ ME/kg DM) to achieve high levels ofmilksolids production.

Question: What is the best energy source touse?Answer: The cheapest, priced per MJ of ME.Generally, very high ME feeds will have maximumlevels at which they can be fed to prevent rumenacidosis, e.g. molasses. Fats, such as tallow oroils, are the most energy dense feeds but havestrict maximum feeding levels to avoid reductionin pasture digestibility (Table 4).

ProteinTheory: Recommended protein levels foroverseas TMR require diets for high producing

cows to contain 18% of the diet DM as crudeprotein, of which 65% is degradable in the rumen,35% bypasses the rumen, and 32% is soluble.New Zealand pastures have 20-30% protein, ofwhich 80% is potentially degradable, 20% isbypass, and 30-40% is soluble. In theory, theprotein profile of high quality pasture does notmeet the recommended levels.

Practice: In practice, high protein pastures meetthe protein requirements for high levels ofmilksolids production. Table 4 shows that theprotein required to produce 20 kg of milk/cow/day will be supplied by high quality pasture if thepasture contains more than 18% crude protein.For higher levels of production (30 kg milk/cow/day) protein requirements will be met if highquality pasture contains more than 24% crudeprotein. Despite the highly degradable nature ofprotein in pasture, the required amount ofmetabolisable protein can be supplied to the cow.This is because, first, rumen microbes growextremely well on high quality pasture, andsecond, the high passage rate out of the rumen(4-7%/h) means that a significant amount ofprotein bypasses the rumen. As a result, proteinsupplements are not required for cows grazinghigh quality pasture.

Question: Should I supplement my cows grazinghigh quality pasture with a bypass protein, suchas fishmeal?Answer: No. The cows are not limited by protein,as long as protein levels in the pasture are above18-20%. In fact, for cows in early lactation thatare losing body condition, bypass protein willincrease the loss of condition.

Question: My cows get 50% of their intake frompasture, and 50% from high energy, low proteinfeeds. Do I need to feed extra protein?Answer: The protein requirements in thissituation will be closer to the recommendationsfor TMR (Table 4), as pasture makes up a smallerproportion of the diet. Check that protein suppliesthe recommended 18% dietary protein. If pastureprotein is 25% and supplement protein is 9%, thenthe ration will have 17% protein, which should beadequate for milksolids production of 2.3 kg/cow/d, provided energy intake is high.

Question: Does high protein pasture (25-35%protein) reduce milksolids production?Answer: Excreting excess nitrogen as ureacertainly requires energy, but the size of this

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Table 4: Nutritional guidelines for all-pasture, pasture + supplement, and totalmixed ration (TMR) diets.

Macro minerals Mineral content of diet required (%DM)All diets, for high production (2 kg MS/cow/day) Calcium 0.6-0.8 Phosphorus 0.4-0.45 Magnesium 0.22-0.28 Potassium 1.0+ Sulphur 0.23 Sodium 0.20 Chlorine 0.25

Guidelines

In intensive systems, start feedingsupplements when: DM intake <15 kg/cow/day (early lactation)

DM intake <12 kg/cow/day (late lactation)Energy Energy requiredAll dietsMaintenance (400 kg lactating cow) 54 MJ ME/cow/dayEvery 50 kg change in LW from 400 kg 5 MJ ME/cow/day MORE or LESS for maintenance

4 weeks before calving requires an extra 25 MJ ME/cow/day for pregnancy2 weeks before calving requires an extra 43 MJ ME/cow/day for pregnancyEvery 1 kg MS requires 62 MJ ME/cow/day(Jersey)

64 MJ ME/cow/day (Crossbred)65 MJ ME/cow/day (Friesian)

Every 1 kg LW gained requires 38.5 MJME/cow/dayEvery 1 kg LW lost supplies 32 MJME/cow/dayProtein Protein content of diet required, (%DM)Good quality all pasture diets kg milk/cow/day kg MS/cow/day 20 1.6 18 30 2.4 24Pasture + supplement, TMR kg milk/cow/day kg MS/cow/day 20 1.6 16 (65% degradable, 35% bypass, 32% soluble) 30 2.4 18 (65% degradable, 35% bypass, 32% soluble)As a general rule for all diets: Early lactation 18 Mid lactation 16 Late lactation 14 Dry cow 12Fibre (% diet DM)Good quality all pasture diets Minimum NDF 35 Minimum effective fibre 17Pasture + supplement, TMR Minimum NDF 27-33 Minimum effective fibre 20 Minimum ADF 19-21Soluble carbohydrate (% diet DM)Pasture + supplement, TMR Maximum total soluble carbohydrate 38 Maximum starch 30Fat (% diet DM)Pasture + supplement, TMR Maximum additional unprotected fat 3 Maximum additional protected fat 3

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energy cost is still uncertain for New Zealand dairycows. At low production levels the real effect maybe small. At higher levels of production (morethan 2 kg MS/day), when the cow is on themetabolic knife-edge, the extra energy requiredfor the synthesis and excretion of urea could besignificant. At these levels of production, reducingthe protein content may reduce the loss of bodycondition, rather than increase milksolids. In thepreviously discussed experiment of Kolver andMuller (1998), the cost of excreting the excessnitrogen was calculated to be worth 0.1 kg MS/cow/day for a cow producing 1.87 kg MS/cow/day.

FibreTheory: The recommended level of fibre for a cowfully fed on TMR requires a minimum of 27-33%of NDF to stimulate chewing and salivaproduction, which in turn helps buffer the rumenpH and promote growth of the rumen microbes(Table 4). This recommended fibre level hasfurther been refined, and the term “effective fibre”(eNDF) is used to describe the fibre that is mosteffective at promoting chewing and salivaproduction. A minimum level of 20% eNDF isrecommended in the diet, i.e. a diet may have30% NDF, of which 67% is effective, resulting inan eNDF of 20%. The theory states that whenthe rumen pH falls below 6.2 and the rumenbecomes more acidic, microbes which digestfibre slow down and digestion is reduced. Theacid detergent fibre (ADF) level can be used as aquick guide to the level of eNDF in a feed.

Practice: In practice these benchmarks requiremodification for pasture diets because first, thefibre levels in fresh pasture are higher than 30%,second, the fibre is much more fermentable (only40-50% of the fibre in good quality pasture maybe “effective”; Kolver et al., 1998), and third, ifstarchy concentrates are not fed then a lowerrumen pH can be tolerated by the rumenmicrobes. Recent research at DRC has shownthat the average ruminal pH of cows fed springpasture (11.8 MJME/kg DM, 42% NDF, 25%protein) is between 5.8 and 6.4 (De Veth andKolver, 1999). Digestibility remained high, evenwhen rumen pH was less than the recommended6.2.

This was further investigated in a laboratoryexperiment that set rumen pH at four levels, 5.4,5.8, 6.2, and 6.6 (De Veth and Kolver, 1999).Digestion was only reduced when rumen pH fell

below 5.8. There are probably two reasons forthe difference between these results for pasture,and overseas recommendations that are basedon high concentrate diets. First, when starchyconcentrates are fed the rumen becomes moreacidic because lactic acid is produced instead ofvolatile fatty acids. Lactic acid depresses microbialgrowth to a much greater extent than volatile fattyacids and also causes acidosis-related healthproblems such as laminitis. Second, whenstarchy feeds are fed, those rumen microbes thatcan digest both fibre and starch will preferentiallydigest starch, thereby reducing fibre digestion.

For pasture diets which include a highproportion of starchy supplement (e.g. more than25-30% of the diet as grains or potatoes), therecommended minimum fibre levels of 27-33%NDF and effective fibre levels of 20% are veryapplicable (Table 4). However, for cows grazingonly high quality pasture, research at DRCsuggests that minimum levels of 35% NDF and17% eNDF may be more appropriate. This meansthat if pasture has less than 35% NDF, asmeasured by a feed analysis, then rumen pH willbe significantly lower than 6.0 and cows will mostlikely respond to supplements of effective fibrelike hay or straw. If the NDF is 42%, as most NewZealand pastures are in spring and autumn, thenrumen pH will not be limiting and cows will notneed or respond to hay.

Question: Should I feed a kg of barley straw tomy cows grazing high quality pasture in springor autumn?Answer: Send a pasture sample away foranalysis (FeedTech, Alan Johns Building,Grasslands Research Centre, AgResearch,Private Bag 11008, Palmerston North, Phone 06356 8019, Fax 06 351 809, two day turn-around;or Animal and Veterinary Sciences Group, LincolnUniversity, Canterbury). If the NDF levels are lessthan 35% (Table 4) then rumen pH will likely betoo low and cows will respond to extra effectivefibre. If the NDF levels are above 35-40% thenrumen pH will be OK and the cows won’t needany straw.

Question: I’m planning on feeding 4 kg DM ofpotatoes and 3 kg DM of barley to cows with apasture intake of 12 kg DM/cow/day (total DMintake of 19 kg/cow/day). What do I do to avoidacidosis and laminitis?Answer: Work out if minimum fibre requirementsare being met (27-33% NDF, 20% eNDF; (Table

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4), and if the amount of starch is below maximumrecommended levels (30%). If starch levels areexceeded, reduce starch input. If fibre levels arenot being met, include an effective fibre source(hay, straw, or silage). Assuming the pasture ishigh quality (42% NDF, of which 50% is effective),the above feeding scenario will result in starchlevels being 30% of the diet (at maximumrecommended levels), NDF at 31% and eNDF13% of the diet (below recommended eNDFlevels). Feeding 2.5 kg DM of potatoes, 2.5 kgDM of barley, and 2 kg DM of hay or straw willsatisfy minimum fibre and maximum starchrecommended feeding levels, and preventacidosis.

Soluble carbohydratesTheory: Diets designed to fully feed the highproducing dairy cow recommend having 34-38%of the diet as soluble carbohydrate (starch,sugars, organic acids), with starch providing nomore than 30% of the diet (Table 4). Theoreticallythese levels are needed to provide the energy tothe cow and the rumen microbes which needenergy to convert ammonia into protein. Theserecommended levels are also used to avoidhealth problems such as acidosis and laminitis.High quality pastures, which contain 5-25%soluble carbohydrate, appear out of balancecompared with the recommended levels.

Practice: The fibre in high quality pasture is veryfermentable, which provides energy for the cowand for efficient growth of rumen microbes. In aseries of experiments at DRC, the effect of addingsoluble carbohydrates to a pasture diet has beendetermined (Kolver 1998). When cows fed highquality pastures are supplemented with solublecarbohydrate, e.g. molasses, grains, potatoesetc., no improvement in rumen microbial growthor milksolids production is observed if overallenergy intake is not increased. On farm thisoccurs when cows are well fed on good qualitypasture, and substitution rate is high. Simplychanging the ratio of soluble carbohydrate:fibrein a high quality pasture diet has little impact onmicrobial growth. If the substitution rate is low, orif soluble carbohydrate supplements are given tocows which have a restricted intake of pasture,milksolids production will increase. This increaseis due to the additional energy supplied to the cow.More microbial protein is produced, but this willonly be of use if the protein requirements of thecow were not being met by pasture, i.e. if proteinlevels in the pasture were less than approximately18-20%.

Question: If my cows are well-fed on high qualitypasture, will I improve digestion and milksolidsproduction if I supplement them with 500 ml ofmolasses?Answer: No. The substitution rate will be highand because the fermentable fibre in pastureprovides readily available energy, overall energyavailability in the rumen will not be increased.

FatTheory: If the base diet contains 3% fat, then anadditional 2-3% of the ration can be fed asruminally unprotected fat, such as vegetable oilsor tallow (Table 4). Generally fats are only used ifvery cheap or if cows are producing more than30 kg milk/cow/day. Feeding too muchunprotected fat will reduce digestion. To get moreenergy into the cows at very high levels of milkproduction (more than 40 kg milk/cow/day), anadditional 2-3% of ruminally-protected fat (e.g.Golden flake, Megalac) may be included in thediet.

Practice: Fresh pasture contains 3-5% fat and atpresent the recommended feeding rates used inrations overseas (above) are probably a goodguide for New Zealand diets.

Question: I have access to a cheap source oftallow. How much should I feed?Answer: For cows with a DM intake of 16-19 kgDM, feeding 0.5-0.6 kg DM of tallow should besafe. If milk protein content drops, feed less tallow.

MineralsTheory: Recommended levels of minerals for thehigh producing cow (e.g. 2 kg MS/cow/day) aregiven in Table 4.

Practice: Cows grazing all-pasture usually requiresupplemental magnesium during spring andsupplemental calcium (e.g. limeflour) if pasturecalcium levels are low (0.2-0.4% calcium). Whenmore than 25-30% of the diet is supplementalfeed, check that mineral requirements are beingmet. Commonly calcium, magnesium, andsodium will be limiting, especially with high maizesilage or grain feeding. This can be remediedusing limeflour, causmag, and agsalt,respectively. Trace minerals can be limiting,especially copper, selenium, and cobalt.Supplying trace minerals two weeks beforecalving and four weeks post-calving can be acheap insurance policy.

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Question: Should I feed limeflour to my grazingcows?Answer: If you are targeting high production (2kg MS/cow/d plus), and your pastures contain lowlevels of calcium (0.2-0.4%) then milksolidsproduction will likely be increased when limeflouris fed and the incidence of milk fever reduced. Inthe long term, pasture calcium levels can beincreased through fertiliser. To prevent milk feverin problem herds, drench with 180-200 g limeflourduring the four days the cows are in the colostrumherd.

AdditivesBefore using additives ask yourself: what is theresponse to this additive?, what are the returns?,and what research is backing up the claims?

Yeast and probiotics: Yeast and probiotics (liveor dead bacteria) claim to enhance digestion bystabilising the rumen environment. Many studieshave been made and the only consistent resulthas been that milksolids responses are variableand cannot be predicted. Even at very high levelsof production (more than 35 kg milk/cow/day) itis difficult to justify the use of these additives.

Enzymes: Fibre-digesting enzymes are alsomarketed, but if the enzyme is not protected fromthe rumen microbes, the enzyme itself will bedigested before it can work. Recent enzymeproducts have been protected against digestion,but like yeast and probiotics, results to date havebeen variable and the use of enzyme products isdifficult to justify.

Chelated minerals: Chelated minerals (mineralsbound to organic compounds) are sold on thebasis that absorption is enhanced whencompared with inorganic minerals. For someproducts improvements in absorption is small,but others can achieve considerably higher levelsof absorption. The main advantage of chelatedminerals is their high solubility, which allows watertrough treatment, e.g. zinc.

Vitamins: Pasture is high in vitamin A and Despecially, and supplements are not required,although responses to other vitamins such as B12

are common when these vitamins are in limitedsupply. If cows respond to vitamin B12 check fora deficiency in cobalt.

Anionic salts: Anionic salts (sulphates, chlorides)can be used in the 2-3 week period before calving

to prevent milk fever, but responses are variable.Achieving the required intake of anionic salts toreduce the DCAD (dietary cation anion difference)to below zero can be difficult. If anionic salts areto be used they must be used in conjunction withother management changes such as using lowpotassium feeds (hay, straw, or maize silage),grazing paddocks with low potassium levels, andensuring that potassium fertiliser isn’t appliedbetween May and September. Concernsregarding the relevance of anionic salts in pasture-based dairying systems have been raised anddiscussed by Roche (2000). Supplementing with100 g Ca for the four days following calving toprevent milk fever is a recommended alternativeto anionic salts.

Rumensin: Rumensin (or monensin) is anionophore which, apart from preventing bloat, canmake the digestive process more efficient byreducing methane and increasing energyavailability to the dairy cow. Rumensin isextensively used in beef feedlots overseas.Supplementation of grazing dairy cows withrumensin has given variable responses that aredifficult to predict.

Buffers: Buffers such as sodium bicarbonate,sodium bentonite, or magnesium oxide, are notrequired for pasture-only diets, but can beeffective if a significant amount (more than 25-30% of the diet) of readily digested grain or starchis fed. Usually buffers are used in conjunctionwith fibre to prevent or treat rumen acidosis.

Feeding to the Cow's Potential

By world standards New Zealand dairy cows havelow per cow production due to a quicker declinein milk production after peak production, and ashort lactation. This is a result of the change inpasture supply and quality during the year, ratherthan genetics, because New Zealand geneticsare internationally competitive.

What is the potential of New Zealand cows toproduce milk when fully fed? At DRC, NewZealand and Overseas Holstein Friesians (HF)of the same breeding worth are being comparedwhen grazing pasture at a low stocking rate(approximately 2.2 cows/ha) or fully fed on TMR.The TMR contains maize silage, grass silage,hay, whole cottonseed, and concentrate based

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on maize, barley, soybean, corn gluten,molasses, fishmeal, oil, protected fat, mineralsand vitamins.

Results from the current season to 5th Aprilare shown in Table 5. Compared to New ZealandHF grazing pasture, New Zealand HF fed TMRproduced 46% more milk, 37% more milksolids,and were 11% heavier. The difference betweenOverseas HF grazing pasture and Overseas HFfed TMR was even greater; cows fed TMRproduced 69% more milk, 54% more milksolids,and were 14% heavier.

Results from the first year of this trial and thecurrent season’s production clearly show thatNew Zealand cows have the potential for highmilksolids production and growth when fed well.These results also suggest that the current highuse of Overseas HF genetics in New Zealand willrequire improved levels of feeding to ensure cowsreach target body condition scores at calving andget in calf.

Conclusions

The New Zealand dairy cow has great potentialto grow and produce milksolids when fed well.The priorities for making money from feedingsupplements to the high producing dairy cow arefirstly to get the appropriate farm system in place,and then to consider feed type. The amount ofsupplementary feed to be used will be determinedby the feed deficits generated within the farmsystem. Which type of supplementary feed to usewill be determined by the amount of supplementsbeing fed and by the nutrients which first-limit

Table 5: Comparative performance of Overseas (OS) and NZ Holstein Friesian cows grazingpasture at a low stocking rate (approximately 2.2 cows/ha) or fed total mixed ration(TMR) ad lib for the 1999/2000 season to 5 April.

Pasture TMR

NZ OS NZ OS

Days in milk 255 227 250 236Milk, kg/cow 3964 3990 5783 6746Milksolids, kg/cow 340 307 467 472Live weight, kg 444 500 495 570Condition score 4.8 3.7 6.7 5.8

References

De Veth MJ, and Kolver ES, 1999. Digestion ofpasture in response to ruminal pH.Proceedings of the New Zealand Society ofAnimal Production 59: 66-69.

Holmes CW, and Wilson GF, 1987. MilkProduction from Pasture. Butterworths, NewZealand.

Kidd JM, 2000. Options For IncreasingProfitability. Proceedings of the RuakuraFarmers’ Conference 52:(in press).

Kolver ES, 1998. Increasing the solublecarbohydrate content of spring pasture diets.Page 8 in: Dairying Research CorporationResearch Update, June.

Kolver ES, and Muller LD, 1998. Performance andnutrient intake of high producing Holstein cowsconsuming pasture or a total mixed ration.Journal of Dairy Science 81: 1403-1411.

Kolver ES, Muller LD, Barry MC, Penno JW,1998. Evaluation and application of the CornellNet Carbohydrate and Protein System for dairycows fed diets based on pasture. Journal ofDairy Science 81: 2029-2039.

Macdonald KA, 1999. Determining how to makeinputs increase your economic farm surplus.Proceedings of the Ruakura Farmers’Conference 51: 78-87.

milksolids production. Nutritional guidelines canbe used to meet the nutritional requirements ofthe high producing dairy cow and to avoid healthproblems.

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National Research Council. 1989. Nutrientrequirements of dairy cattle. 6th rev. ed.National Academy Press, Washington, DC.

Penno JW, 1998. Principles of profitable dairying.Proceedings of the Ruakura Farmers’Conference 50: 1-14.

Roche JR, 2000. Feeding The Transition Cow -The Myths And The Magic. Proceedings of theRuakura Farmers’ Conference 52:(in press).

Van der Poel J, 1996. Going for high production.Proceedings of the Ruakura Farmers’Conference 48: 5-10.