growth, development and composition of the udder …€¦ · to describe growth of different...

GROWTH, DEVELOPMENT AND COMPOSITION OF THE UDDER AND GRAVID UTERUS OF BEEF HEIFERSDURING PREGNANCY

C. L. Ferrell 1 , W. N. Garrett and N. Hinman

University o f California 2 , Davis 95616

SUMMARY

Forty-six Hereford heifers were slaughtered at different stages of gestation. Udders and gravid uteri were removed. Each gravid uterus was dissected into fetus, fetal membranes, fetal fluids and uterus. Fresh weights, dry matter, ether extract, ash, nitrogen and gross energy contents of the various tissues were determined. Weights and compositions of udders and uteri from 36 non-pregnant heifers were also determined. Relationships of the type W = Woe (b~-b2t) t where t is the number of days after mating, Wo is the amount of constituent on the day of mating and W is the amount of constituent on day t of gestation were derived to describe growth of different constituents of the gravid uterus during gestation.

Udder development was most rapid after 234 days of gestation as indicated by ash and nitrogen contents. Udders of pregnant heifers contained approximately 48, 60, 67 and 102 g nitrogen at 134, 189, 237 and 264 days of gestation, respectively and udders of non-pregnant heifers contained approximately 37 g nitrogen. No net accumulation of energy occurred in udders of pregnant heifers re/ative to that gained in udders of non-pregnant heifers.

Fetuses averaged 1.58, 7.53, 20.8 and 31.6 kg and contained 1.20, 1.60, 2.07 and 2.52% nitrogen at 134, 189, 237 and 264 days of gestation, respectively. Gross energy contents of fetuses were .54, .88, 1.17 and 1.32 kcal/g fresh weight at each of these times. Rates of nitrogen and energy storage in the gravid uterus were estimated to be .76, 2.79, 8.95 and 25.0 g/day and 36.0, 143,457 and 1,167 kcal/day at 100, 160, 220 and 280 days of gestation, respectively. None of these values was affected by fetal sex or maternal energy intake (150 or

1Present address: U.S. Meat Animal Research Center, Clay Center, Nebraska.

2 Department of Animal Science.

215 kcal ME/Wa/4/day). kg

(Key Words: Fetus, Gravid Uterus, Udder, Nitrogen, Energy, Growth.)

INTRODUCTION

Information concerning prenatal growth of the bovine has been primarily limited to birth weight (Andersen and Plum, 1965; Hight, 1966) or weight and linear measurements of the fetus at different stages of gestation (Lyne, 1960, Swett et al., 1948; Winters et al., 1942). Jakobsen (1956) and Jakobsen et al. (1957) have provided limited data concerning the weight and composition of the bovine fetus and other tissues of pregnancy at different stages of gestation. These latter reports have been heavily relied upon for the estimation of nutrient requirements for pregnancy in cattle (A.R.C., 1965; N.R.C., 1971). More extensive data concerning prenatal growth and composition of the tissues of pregnancy in the bovine are essential to provide a sound basis for the estimation of nutrient requirements for pregnancy in cattle.

The purpose of this study were to determine weights and compositions of the fetus, fetal membranes, fetal fluids (amnionic and allantoic fluids), uterus and udder at various stages of gestation in Hereford heifers and to develop relationships to describe growth of these tissues during gestation; and thus, provide more extensive basic data necessary for the estimation of nutrition requirements of cattle during gestation.

MATERIALS AND METHODS

Animals. Eighty-two heifers (mean weight, 275 kg) predominately of Hereford breeding were obtained from commercial sources. Ani- mals were from an experiment reported by Ferrell (1975). Forty-six heifers were separated at random and hand mated to three Hereford bulls during a 50-day mating period. All heifers

1477 JOURNAL oF ANIMAL SCIENCE, Vol. 42, No. 6, 1976

1478 FERRELL, GARRETT AND HINMAN

were fed a 1:1 mixture of chopped alfalfa (Ref. No. 1-00-068) and oat hay (Ref. No. 1-03-280) ad libitum during the breeding period. Bred heifers were 42 + 1 (mean + SE) days pregnant when the feeding trial started. Ten heifers were slaughtered at the initiation of the trial and are hereafter referred to as the initial slaughter group. During the feeding trial the remaining 72 heifers were penned in individual pens (1.5 x 6.7 m) under an open pole barn and fed once daily a mixed diet consisting of alfalfa hay (45.0%, Ref. No. 1-00-068), rolled barley (40.5%, Ref. No. 4-07-939), beet pulp (7.0%, Ref. No. 4-00-069), molasses (6.0%, Ref. No. 4-04-696), salt (1.0%, Ref. No. 6-04-152)and dicalcium phosphate (.5%, Ref. No. 6-01-080). The metabolizable energy (ME) content of this diet was 2.55 + .04 kcal/g DM (Ferrell et al., 1976). One-half of the pregnant and non-pregnant heifers were fed at either 150 or 215 kcal ME/W3/4/day, where W is empty body weight.

kg Feed allowances were adjusted monthly. Preg- nant heifers, selected at random from both the high and low levels of intake, were slaughtered at approximately 134, 189, 237 and 264 days of gestation. Non-pregnant heifers from both the high and low level fed groups also were slaughtered with each of these groups.

Slaughter, Sampling and Analyses. At slaughter, udders were removed and uteri were severed at the cervix and removed. The gravid uterus of each pregnant heifer was dissected into fetus, fetal membranes, fetal fluids (allantoic and amnionic fluids) and uterus. Weights of the fetus, fetal membranes and uterus were recorded and weight of the fetal fluids was determined by difference. Fetal heart girths and curved crown-rump lengths were taken as described by Lyne (1960) for all fetuses and straight crown-rump lengths were recorded for fetuses from heifers slaughtered at 189, 237 and 264 days of gestation. Samples of fetal fluids (500 g) and fetal membranes (300 g) were taken. Uteri and entire udders were ground fresh and fetuses were ground frozen. Single samples of the uteri and udders and duplicate samples (150 g) of the fetuses were taken. All samples were stored frozen ( - 1 5 C) until analyzed.

All samples were freeze dried. Samples of uteri, udders and 189-, 237- and 264-day-old fetuses were combined within tissue, physiolog- ical state and slaughter period then placed into large Soxhlet apparatuses and extracted with

diethyl ether for 7 days. Extracted samples were then dried in forced-air ovens at 100 C for 18 hours. Fat content was assumed to be the difference in dry weights before and after ether extraction. Samples of the ether extract were saved for determination of heat of combustion. Samples of the dry membranes, fetal fluids and 134-day-old fetuses and dry, extracted samples of udders, uteri and the 189-, 237-, and 264-day-old fetuses then were ground. Samples of fetal fluids, fetal membranes and 134-day- old fetuses were extracted fo r 12 hr with diethyl ether on a Goldfisch apparatus to determine ether extract contents of the dry material. Ash (575 C for 15 hr), nitrogen (macro-Kjeldahl) and heat of combustion (adi- abatic bomb calorimetry) were determined for all dry, (134-day-old fetuses, fetal membranes and fetal fluids) and dry ether extracted (189-, 237-, 264-day-old fetuses, udders and uteri) samples, and heats of combustiorl were determined for ether extract samples from uteri, udders and 189-, 237-, or 264-day-old fetesus.

Data were analyzed statistically by use of analysis of variance. Two-way or three-way factorial models were used where appropriate. Duncan's multiple range test (LeClerg, 1957) was employed for comparison of means. A model, similar to that of Koong et al. (1975), of the type W = Woe(b1 + b2t + b3L)t where t is day of gestation, L is feeding :level (kcal ME/W~/4/day), W o is amount of component on

day zero of gestation and W is amount of component on day t o f gestation was used to mathematically describe growth of various tissues or components of various tissues of pregnancy during gestation. A stepwise regression technique (Dixon, 1970) was used as described by Koong et al. (1975) to fit the model with experimental data. Linear regression analyses were used to describe relationships between fetal age or weight and linear measures of fetal size.

RESULTS AND DISCUSSION

Mean empty body weights of heifers at slaughter of the major treatment groups were as follows: initial slaughter, 265 -+ 8; non-pregnant fed at the low level, 331 + 9 ; pregnant fed at the low level, 335 + 8; non-pregnant fed at the high level, 383 + 10 and pregnant fed at the high level, 412 + 9 kilograms.

Heats of combustion of various gross chemical fractions of tissues of gravid uteri and

PRENATAL GROWTH OF THE BOVINE 1479

TABLE 1. HEAT OF COMBUSTION OF DIFFERENT FRACTIONS OF TISSUES OF PREGNANCY (MEAN + SE)

No. of Heat of combustion Tissue Fraction a samples (kcal/g)

Udder FFOM 82 5.575 +- .011 Ether extract 9 9.555 + .055

Uterus FFOM 81 5.667 -+ .008 Ether extract 9 9.518 + .045

Fetus FFOM 46 5.505 + .011 Ether extract 3 9.527 + .078

Fetal fluid DM 46 3.568 _+ .088

Fetal membranes DM 46 4.878 _+ .020

aFFOM and DM represent fat-free organic matter and dry matter, respectively.

udders are presented in table 1. Gross energy contents of dry fat-free organic matter (FFOM) of these tissues were similar to values of 5.532 and 5.539 kcal/g reported by Garrett and Hinman (1969) for heats of combustion of carcass and empty body FFOM. Heats of combustion of ether extract from various tissues were similar to the value of 9.5 kcal/g proposed by Armsby (1917). Gross energy contents of all tissues of the gravid uterus obtained in this study were comparable to values determined by Jakobsen e t al. (1957) when expressed on the same basis.

Fresh weights and gross chemical composition of uteri of nonpregnant heifers are given in table 2. There were no differences in the weight or composition of uteri due to time on feed; thus data were combined, within feeding level. Uteri from heifers slaughtered initially were smaller (P<.05) than those from heifers slaughtered later in the study possibly due to these heifers being less mature than those slaughtered later. Although there were no differences (P>.05) in fresh weight, percentage ash or percentage nitrogen of uteri due to feeding level, uteri from heifers fed at the high level had a higher (P<.05) fat content, hence a higher (P<.05) dry matter content and a higher (P<.05) concentration of gross energy, than did uteri from other non-pregnant heifers.

Values for udder fresh weights and contents of dry matter, ether extract and gross energy are presented in table 3, by treatment group. All of these values were increased by increased level of feed and by time on feed. Pregnancy resulted in an increase (P<.001) in fresh udder weight but did not alter dry weight, ether

extract or gross energy contents of the udder. These latter results indicate udder development has little effect upon energy requirements for gestation in heifers of this type. An interaction (P<.05) between pregnancy and time in the case of fresh udder weight, indicative of an increased udder weight in latter stages of gestation, was observed.

Ash and nitrogen contents of the udders from heifers slaughterd initially were 4.79 • .25 and 22.2 • 1.2 gram. Udders from other nonpregnant heifers contained 8.67 -+ .48 g ash and 36.6 • 1.6 g nitrogen. These latter values did not change (P>.05) due to feeding level or time on feed. Relationships, in pregnant heifers, between udder nitrogen or ash and day of gestation are depicted graphically, by feeding level, in figure 1. Assuming total udder nitrogen and ash are adequate indices of udder development, data in figure 1 indicate greatest udder development occurred during the latter stage of

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gestation. The t rend toward lower nitrogen contents, at 264 days of gestation, of udders from heifers fed at the high level compared to those from heifers fed at the low level suggest that excessive fatness of heifers may be detri- mental to udder development during gestation. This latter observation is consistent with the research of Reid et al. (1957) and Swanson (1957) who found indications of an inverse relationship between feeding level early in life and milk production later in life. A large increase in variation of udder nitrogen at 264 days of gestation in relation to variation early in gestation was observed (figure 1) and may reflect an expression of different genetic poten- tials for subsequent milk production.

There were no differences (P>.05) in fresh weights or gross chemical composit ions of the uteri of pregnant heifers, fetal fluids, fetal membranes or fetuses due to feeding level. As a result, data from heifers fed at the two levels were combined. Mean values for the weights and compositions of the tissues of gravid uteri are presented in table 4. These heifers were fed considerably above maintenance in order to insure that maternal tissues were in a positive energy balance, thus these results are consistent with those of other investigators (Hight, 1966; Morris, 1970; Tudor, 1972) who have observed decreases in calf birth weight only in cases of severe under-nutrit ion.

No differences were observed in composit ion of the uteri of pregnant heifers due to stage of gestation. Composit ion (table 4) was relatively constant at approximately 16.6% dry matter, 3.0% fat, 1.14% ash, 2.12% nitrogen and .95 kcal/g. These values, with the exception of ash, are lower (P<.05) than corresponding values for uteri from non-pregnant heifers (table 2). Fresh uterine weights were f i t ted to the model of Koong et al. (1975), described previously, to describe the relationship between u te r ine weight and day of gestation. The regression derived was as follows:

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that observed in the initial slaughter group of heifers (table 2). This regression indicates that the initial instantaneous growth rate of the uterus was about 2.03% per day and that the rate of growth declined at a rate of .00268% for each day as gestation advanced.

Weight of the fetal fluids (table 4) increased rapidly early in gestation, did not change between 189 and 237 days of gestation, and increased rapidly between 237 and 264 days of gestation. The composition of the fluid was variable, but was consistently very low in dry matter (2.0 to 3.7%), hence, low in all other components when expressed as percentages of fresh weight. Dry matter and nitrogen percentages and gross energy concentration in the fluid were lower (P<.05) in the first than in the other three slaughter groups; otherwise, there was little meaningful difference in composition of the fluid at different stages of gestation.

There was no difference in fat or ash contents of fetal membranes (table 4), when expressed as percentages of fresh weight, due to stage of gestation. Percentage of dry matter and nitrogen increased during the first three periods but not during the last. Fresh weight of fetal membranes (table 4) followed a pattern similar to that of the uterus during gestation. As with the uterus, the model proposed by Koong e t al.

(1975) was also used to describe the growth of the fetal membranes during gestation. Feeding level was not a significant factor in the relationship between membrane weight and day of gestation. The equation derived was as follows:

w = 41.17e(.0236-.0000294t) t (n = 46, R = .96, cv = 2.80%)

The coefficient bi was highly significant (P<.001), whereas, b2 approached significance (P<.01) but was included in the final relationship in order to obtain a more reasonable estimate of membrane weight during early gestation. The relationship derived indicates that the initial instantaneous growth rate was about 2.36% per day and that this rate declined at a rate of .00294% for each day of gestation.

Percentages of all components of the fetus (table 4) increased throughout gestation with the exception of fat. Although not significant, percentage fat in fetuses at 264 days tended to be higher than in those at 237 days of gestation. The equation derived to mathematically describe fetal growth was:

w = Woe(-0512-.0000707t)t (n =46, R= .996, cv= 1.13%)

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and has been presented graphically in figure 2 as have the relationships between both fetal membranes and uterine fresh weights and day of gestation. Fetal weight was very low, relative to weights of uterus and fetal membranes in early stages of gestation but increased rapidly during the second and third trimesters. Fetal weight represented 19.2, 36.8, 56.8 and 57.5% of gravid uterus (fetus, fetal fluids, fetal membranes and uterus) weight at 134, 189,234 and 264 days of gestation, respectively, and ap- peared to approach a maximum of 57 to 58% near term.

Estimated fetal, fetal membranes and uterine weights at parturition were obtained by extrap- olation of the appropriate regression to 286 days of gestation (Andersen and Plum, 1965). The values obtained were 41.1, 4.2 and 7.6 kg for the fetus, fetal membranes and uterus, respectively. Weights of these tissues at various days of gestation were then expressed as percentages of predicted final weight and presented graphically in figure 3. When so expressed, these data indicate uterine development preceded fetal membrane development which in turn preceded fetal development. These data support the contention (Dawes, 1968) that fetal development is dependent upon prior development of the uterus and fetal membranes which are necessary to supply nutrients to the developing fetus.

Data concerning weights and compositions of tissues of the gravid uterus of Red Danish cows at different stages of gestation have been reported by Jakobsen (1956) and Jakobsen e t

al. (1957). Weights and compositions of uteri, fetal membranes and fetal fluids were similar to


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those reported in table 4. Weights and compositions of the placenta and fetal fluids of a Jersey cow near term (Eckles, 1916) were similar to corresponding values obtained in this study.

The fetal data reported in the present study resemble those reported by Winters e t al.

(1942), Jakobsen (1956) and Jakobsen e t al. (1957). Fetal weights (table 4) were similar to those reported by Lyne (1960) at early stages of gestation, but were higher near term. Older fetuses (264 days) in this study contained higher percentages dry matter and fat and lower percentages ash and nitrogen than newborn Hereford calves (Haig e t al., 1920) and weighed only 3.0 kg less than the average birth weight of Hereford calves (Andersen and Plum, 1965) even though they were approximately 20 days prepartum.

Positive relationships (P<.001) were observed between day of gestation and heart girth, curved crown-rump length or straight crown- rump length (table 5). Any of these measures of fetal size appear to be precise indices of fetal age, as indicated by the high correlation coefficients and the low coefficients of variation, over the range of fetal ages available in this study. These regressions do not predict fetal ages accurately early in gestation, thus should not be extrapolated beyond the scope of these data (125 to 273 days of gestation). Data in the present study and that of Winters e t al. (1942) and Lyne (1960) suggest linear relationships between day of gestation and linear measures of fetal size beyond 120 days of gestation. Prior to 120 days curvilinear relationships were indicated. Data on fetuses 120 days of age or more (Winters e t al., 1942; Lyne, 1960) suggest relationships similar to those derived in the

present study. Significant (P<.001) relationships of a para-

bolic nature (log-log regressions) were found between fetal heart girth, curved crown-rump length or straight crown-rump length and fetal weight (table 5). The high correlation coefficients and low coefficients of variation indicate that these linear measures of fetal size are good indices of fetal weight over the range of data available in this study. These regressions indicate that linear measurements increase in pro- portion to approximately WX/3, or weight increase is approximately proportional to linear size cubed. In this regard, these data resemble those for postnatal cattle (Brody, 1945).

The model proposed by Koong e t al. (1975) was used to derive mathematical relationships representing growth of the fetus, conceptus and gravid uterus in terms of fresh weight (g), weight of nitrogen (g), or gross energy (kcal) during gestation (table 6). The coefficient, b3, for ME intake was not significant in any of these relationships. The high correlation coefficients and low coefficients of variation of these regressions indicate they may be useful for the prediction of the fresh weight, nitrogen, or energy content of tissues of pregnancy at different stages of gestation.

The coefficients bx and b~ were significant (P<.001) in the three relationships representing fetal growth. That the coefficient b2 was significant and negative indicates that relative growth rate of the fetus in terms of weight, nitrogen or energy was not constant as assumed by a simple exponential function, but a variable which decreased as pregnancy progressed. This is consistent with data of Winters (1942), who showed that relative growth rate of bovine fetuses was greatest in early gestation and declined as pregnancy advanced. Relationships derived in this study indicate initial rate of weight gain of the fetus was about 5.1% and declined at a rate of .007% for each day of gestation. Similarly, rates of nitrogen and energy retention in the fetus on day zero were estimated to be 5.4 and 6.9% and declined at rates of .006 and .009%, respectively for each additional day of gestation.

Relationships, similar in form to those obtained to represent fetal growth, were derived to mathematically describe growth of the conceptus (fetus, fetal fluids and fetal membranes) and gravid uterus (conceptus and uterus) during pregnancy. The coefficients bl and b2 were significant (P<.001) in the regressions which


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represent the retention of nitrogen and energy in the conceptus and gravid uterus as pregnancy advanced. These relationships, involving the gravid uterus, are presented graphically in figure 4 and 5. The similarity of the shape of these curves is indicative of the high correlation (logqog, r = .999) between nitrogen and energy contents of the gravid uterus. Although impre- cise values were predicted in early gestation, these figures demonstrate the very low energy and nitrogen contents in gravid uterine tissues during early gestation in relation to the amounts stored during late gestation. The coefficient bl was highly significant (P<.O01) in the regressions representing weight of the conceptus and gravid uterus at different stages of gestation. The coefficient b2 (P<.I0) was included in these relationships in order to obtain more reasonable estimates of the weights of these tissues early in gestation and -. ar term.

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TABLE 7. PREDICTED DALLY GAIN OF NITROGEN AND ENERGY BY THE FETUS, CONCEPTUS OR GRAV1D UTERUS AT DIFFERENT STAGES OF G E S T A T I O N

1487

Fetus Conceptus a Gravid uterus b

Day of Nitrogen Energy Nitrogen Energy Nitrogen Energy gestation (g) (kcal) (g) (kcal) (g) (kcal)

100 .2 9 .4 15 .8 36 130 .6 31 .9 45 1.5 74 160 1.6 89 2.2 114 2.8 143 190 3.6 211 4.5 244 5.1 263 220 7.3 411 8.2 440 9.0 457 250 12.9 644 13.3 658 15.2 752 280 19.8 785 18.9 793 25.0 1167

aconceptus = fetal plus fetal fluids plus fetal membranes.

bGravid uterus = conceptus plus uterus.

have indicated deposition of nitrogen and energy in the gravid uterus may be expressed as simple exponential functions of t ime after conception. Although simple exponential relationships, obtained in this s tudy to describe p rena ta l growth, were highly significant (P<.001), functions in which the instantaneous growth rate decreased as pregnancy advanced gave much bet ter estimates of fresh weight, nitrogen or energy contents of the uterus, fetus, fetal membranes, conceptus and gravid uterus during early gestation and, more important ly from a nutrit ional point of view, near term. Koong e t al. (1975) and Laird (1966) have obtained similar results when relating f e t a l weight of various species to t ime after conception.

Rates of nitrogen or energy storage in the fetus, conceptus or gravid uterus were obtained by differentiation of the appropriate relationship (table 6) with respect to day of gestation. The daily gain of nitrogen and energy by the fetus, conceptus and gravid uterus was calculated for several days of gestation (table 7). Little nitrogen or energy deposition occurred in these tissues during the first half of gestation, but the rate of deposition became relatively large during lat ter stages. For instance, at 280 days of gestation the predicted rate of storage of nitrogen and energy in the gravid uterus was 25 g and 1.17 Mcal per day, respectively. These estimates are similar to those of Jakobsen (1956) and Jakobsen e t al. (1957) during early gestation but slightly higher during the latter stages. This observation apparently is largely a result of the different types of mathematical expressions used to represent prenatal growth.

Jakobsen (1956) has indicated udder nitrogen increased approximately 200 g during gestation in Red Danish heifers. Data obtained in the present s tudy suggested a retention of about 60 g nitrogen in udders of Hereford heifers during pregnancy. These results suggest large differences in udder nitrogen deposition in cattle having different milk production poten- tials. Both of these estimates indicate udder nitrogen retention was negligible in relation to nitrogen retention in tissues of the gravid uterus. Also, it is probable that udder nitrogen retention would be less in second and later pregnancies. Data of Ferrell (1975) suggested little net nitrogen retention in non-reproductive tissues of heifers during pregnancy. These re- suits suggest protein requirements for pregnancy may be est imated from nitrogen retention in gravid uterine tissues.

Estimates of supplementary available protein requirements on different days of gestation (table 8) were calculated from estimated rates of nitrogen retention in gravid uterine tissues (table 7) by factorial procedures (A.R.C., 1965) assuming a biological value of dietary protein of 70%. Changes in endogenous nitrogen losses were assumed to be negligible. Metabolizable energy requirements (table 8) for pregnancy were calculated from estimated rates of energy deposition in gravid uterine tissues assuming an efficiency of utilization of ME for deposition in gravid uterine tissues of 14% (Ferrell e t al.,

1976). Estimates of supplementary digestible protein required on different days of gestation were calculated from available protein needs assuming additional dry matter intake of a ration containing 1.8 Mcal ME/kg dry matter to meet


TABLE 8. SUPPLEMENTARY REQUIREMENTS OF AVAILABLE PROTEIN, DIGESTIBLE CRUDE PROTEIN AND METABOLIZABLE ENERGY OF PREGNANT COWS FOR

GROWTH OF TISSUES OF TIlE GRAVID UTERUS

Available a Digestible b Metabolizable c Day of protein protein energy gestation (g/day) (g/day) (kcal/day)

100 7 12 260 130 13 21 530 160 25 43 1020 190 46 79 1880 220 80 137 3260 250 136 229 5370 280 223 368 8340

aSupplementary available protein was calculated by factorial methods assuming calf birth weight to be 41 kg as follows: AP = (n • 6.25)/.70 where AP is the estimated supplementary available protein requirement for pregnancy in grams per day, n is the nitrogen stored in gravid uterine tissues in grams per day and .70 is the biological value of dietary protein for cattle (A. R.C., 1965).

bsupplementary digestible protein requirements were calculated from available protein requirements assuming supplementary intake of a diet containing 1.8 Mcal ME/kg to meet estimated ME requirements for pregnancy and metabolic fecal nitrogen of 5 g/kg (A.R.C., 1965) supplementary dry matter intake.

CSupplementary metabolizable energy requirements were estimated from rates of energy deposition in the gravid uterus assuming an efficiency of 14% (Ferrell, 1975).

the add i t iona l ME r e q u i r e m e n t for p r egnancy and 5 g me tabo l i c fecal n i t rogen per k i logram add i t iona l d ry m a t t e r in take .

Es t imates of s u p p l e m e n t a r y avai lable and di- gest ible pro te in requi red for g rowth o f t issues of t he gravid u terus ( t ab le 8) were s imilar to es t imates o b t a i n e d by A.R.C. ( 1 9 6 5 ) and J a k o b s e n ( 1 9 5 6 ) for l a t t e r stages of ges ta t ion , bu t s l ightly lower dur ing earl ier stages. These es t imates ind ica te add i t iona l p ro te in needed for p regnancy were o f l i t t le prac t ica l i m p o r t a n c e dur ing early ges ta t ion bu t b e c a m e relat ively high dur ing la t ter ges ta t ion. Fo r example , available p ro t e in needed at 280 days of ges ta t ion was a p p r o x i m a t e l y 223 grams. The A.R.C. (1965) e s t ima ted available p ro t e in requi red by a 4 5 0 kg m a t u r e c ow a t m a i n t e n a n c e to be 110 g.

Metabo l izab le energy r e q u i r e m e n t s for pregnancy ( tab le 8) fo l lowed a p a t t e r n similar to t ha t of p ro te in . Es t ima ted ene rgy r e q u i r e m e n t s were low dur ing earlier stages o f ges ta t ion b u t increased rapid ly dur ing la t t e r stages. Es t imates o b t a i n e d were sl ightly lower t h a n those ob- ta ined by Moe and Tyrrel l ( 1971) b u t considerably higher t h a n those of A.R.C. (1965) .

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growth, development and composition of the udder …€¦ · to describe growth of different...

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