MILK PRODUCTION IN HEREFORD COWS

Transcription

1 MILK PRODUCTION IN HEREFORD COWS I. MEANS AND CORRELATIONS 1.2 O.W. Robison, M.K.M. Yusuff 3 and E.U. Dillard North Carolina State University, Raleigh SUMMARY Milk production in Hereford cows was studied utilizing 1,319 lactation records on 528 cows. The data were collected from two related herds over an 8-year period (1968 to 1975). Estimates of milk yield were obtained at bimonthly intervals by the calf-suckling technique. The three within-lactation observations (M1, M2 and M3), the sum of the three observations (TMY) and a predicted sum of seven monthly observations (PMY) were used as estimates of milk yield. Least-squares means for the five measures were 5.9, 5.7, 4.7, 16.2 and 39.0 kg, respectively. Herd, year, herd by year and age ofcowaffected (P<.01) all measures of milk yield. Year effects fluctuated greatly during the first 4 years, but there was little fluctuation during the last 4 years. No apparent time trend was evident. Age of cow effects were significantly curvilinear with yield increasing from 2 to 5 years of age, little difference between 5 to 8 years and a decline in cows older than 8 years of age. Birth weight affected (P<.05) all measures of milk yield with heavier calves obtaining more milk. Female calves received slightly more (P>.05) milk than bull calves. Phenotypic correlations, after adjustment for the above environmental effects, were calculated between measures of milk yield and measures of growth. The correlations between 205-day weight and M1, M2, M3, TMY and PMY were.48,.48,.44,.63 and.63, respectively. Milk yield was similar for the first 2 months of lactation and declined thereafter. Milk supplied sufficient energy to meet the calf's needs for ~Paper No of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh. 2Conducted in cooperation with the Southern Regional Project S-10, The Improvement of Beef Cattle for the Southern Region through Breeding Methods. 3Present address: Malaysian Agricultural Research and Development Institute, Serdang, Selangor, Malaysia. maintenance and growth only during the first month. By the fifth month milk did not supply sufficient energy to meet maintenance requirements. (Key Words: Milk Production, Hereford Cows, Weaning Weight.) INTRODUCTION In cow-calf operations weaning weight of the calf exerts a great influence on net income. While weaning weight is influenced by many factors, several workers from Knapp and Black (1941) to Rutledge et al (1971) have shown milk supply to be the single most important component. Further, Rutledge et al (1971) showed that it was quantity, not quality, of milk that was important. Estimates of the percentage of variation in weaning weight accounted for by milk volume range from 20 to 60%. Due to the great influence of milk volume on weaning weights, it is important to characterize the lactational performance of beef cows. Two methods for estimating milk production are calf nursing and hand milking after oxytocin injection. Totusek and Arnett (1965), Dawson et al. (1960) and Wistrand and Riggs (1966) concluded that the calf nursing procedure was adequate for estimating milk yield. Rutledge et al. (1972) evaluated various sampling schemes to characterize the producing ability of beef cows. They concluded that bimonthly milk samples were sufficiently accurate to be used in estimation of milk yield. When their equations were tested on two indedent data sets, the correlations between estimated and observed milk yield were greater than.90. The objectives of this study were to evaluate some factors affecting milk yield and to estimate the relationships between milk production and various production criteria. MATERIALS AND METHODS The data used in this study were collected from two related herds of Hereford cattle located at 131 JOURNAL OF ANIMAL SCIENCE, Vol. 47, No. 1, 1978

2 132 ROBISON, YUSUFF AND DILLARD Raleigh and Plymouth, NC. The data set consisted of 1,319 lactation records from 528 cows collected from 1968 to Nine or more service sires were used each year. Bulls were used only 1 year and at both locations. The service sires used the last 5 years were selected for weaning weight, postweaning gain or randomly. Only the cows born after 1971 would have selected bulls as sires. All heifer calves were put in the breeding herd to calve at 2 years of age. If they did not calve they" were given a second opportunity at 3 years of age. All cows 3 years or older and not pregnant were culled. Essentially all culling of cows was on the basis of reproductive performance. Artificial insemination was employed and the breeding season was approximately 90 days. Male calves were weaned as bulls and no creep feeding was practiced. Cows and calves were maintained on pasture with corn silage and protein supplement provided during the winter months. Silage feeding lasted about the first 90 days of the calving season. Milk production was estimated bimontly at approximately equal intervals. Three measurements were obtained for each lactation. The procedures followed Rutledge et al (1972). Briefly, cows and calves were separated at approximately 8 am and at 4 pm the calves were weighed, allowed to nurse and after completion of nursing (15 to 20 min) reweighed. Cows and calves remained separated overnight. The following morning at 8 am the calves were weighed, allowed to nurse and reweighed. Weights were recorded to the nearest pound. The sum of the differences between these two postnursing and prenursing weights represents an estimation of 24-hr milk yield. Age of calf at first sampling ranged from 6 to 69 days. Thus a cow was either in the first or second month of lactation when the first sample was obtained. Milk production of the cows was estimated according to two sampling schemes, i.e., first, third and fifth month of lactation (1-3-5) or second, fourth and sixth month of lactation (2-4- 6). The milk yield variables studied were: a) The three within-lactation observations. These were denoted as M1, M2 and M3, respectively. b) Total milk yield (TMY) was the sum of the three within-lactation observations. c) Predicted milk yield (PMY) was obtained using the regression equations derived by Rutledge et al. (1972) and defined as the sum of seven monthly 24-hr milk yields. In addition, weight of calf at birth, at each milk sampling period and at 205 days, was recorded. The age of cow and lactation number for each record was available also. The data were analyzed according to procedures outlined by Harvey (1975). Least-squares procedures were used for Models I and II; maximum likelihood procedures were used for Model III. Model I: Model II: Model III: Yijk/mno~ # + S~ + C~j + Hk + T/+ (TH)k/+ Am A- D. + b (X ~ik/mno-- Xiik/mn) "~- eiik/mno; Same as Model I except C~j was deleted; Same as Model I except cow effects were adjusted for incomplete repeatability. Where Yiik~m,o = the individual observation for a given dependent variable, ~ = the overall mean; S~ = random effect of the i th sire; C~j = random effect of the j~h COW within the i th sire; Hk = fixed effect of the k th herd; Tt = fixed effect of the f, year; Am = fixed effect of the mth age of cow; D, = fixed effect of n 'h sex of calf; THkz = interaction effects; b = partial regression coefficient; X~jk~m,o= birth weight of the calf and e~i~m.o = the random element associated with Y RESULTS AND DISCUSSION Means, standard deviations and coefficients of variation for measures of milk yield are shown in table 1. The mean milk yield decreased as stage of lactation increased, Coefficients of variation were large for individual observations of milk yield while for TMY and PMY they were in the range generally observed for such traits as weaning weight, average daily gain, efficiency, etc. Herd, year, age of cow and herd by year interaction effects were important (P<.01) for all measures of milk yield. Comparisons of age of cow and year constants for PMY derived from the three models are presented in tables 2 and 3. In Model I least-squares procedures were used and cows were included in the model, whereas in Model II leastsquares procedures were used but cows were not included in the model. Model III included cows in the model, but maximum likelihood procedures were used. Due to the large turnover in the cow herd during the study, a solution to Model I was feasible. In fact, the determinants of the three models did not differ appreciably. However, age of dam and year constants were quite different depending on the model used. The estimates derived from Models II and III did not differ appreciably but were quite different from the estimates obtained utilizing Model I.

3 MILK PRODUCTION IN HEREFORDS--MEANS, CORRELATIONS 133 TABLE 1. MEANS, STANDARD DEVIA- TIONS AND COEFFICIENTS OF VARIA- TION FOR MILK YIELDa TABLE 2. LEAST SQUARES VS MAXIMUM LIKELIHOOD CONSTANTS (PMY) a FOR AGE OF COW Trait b X SD c CV L.S. L.S. Age (cows (cows M included) excluded) M.L. M M TMY PMY akilograms bm1, M2, M3, TMY and PMY are observa tions made in first 60 days, second 60 days, third 60 days of lactation, sum of M1, M2 and M3 and predicted 7-month milk yield, respec tively. CStandard deviations calculated from residual mean squares (Model IlI). akilograms. Model I suggests a continuous and marked decline in milk production with increasing years, whereas Models II and lli suggest a more random fluctuation. Likewise for age of cow, Model I shows a continuous improvement with increasing age of cow with cows/> 10 yr producing the most milk. Models II and III show cows age 5 to 8 years producing the most with younger and older cows producing less milk. Results of Models II and III agree with generally accepted effects of age of cow on weaning weights and with age of cow effects in dairy data. It is apparent that Modei I is not an appropriate model and leads to biased estimates of year and age of cow constants. Henderson et al. (1959) and Henderson (1972) pointed out the biases involved in estimating environmental trends Figure 1. Age of cow effects on measures of milk yield. TABLE 3. LEAST SQUARES VS MAXIMUM LIKELIHOOD CONSTANTS (PMY) a FOR YEARS L.S. L.S. (cows (cows Year included) excluded) M.L akilograms. 251 O" --~ O! "O5 i.1.01 // TMY mmi / M2 em3 9 ".\- o Y I ) i I I I I I I0 AGE OF COW [years]

4 134 ROBISON, YUSUFF AND DILLARD TABLE 4. EFFECTS OF BIRTH WEIGHT AND SEX ON MILK YIELD (KG) Birth weight Sex Trait a (b) (F-M) M1.062**.034 M2.040**.135 M3.033*.145 TMY.126"*.208 PMY.287**.525 *P (.05, **P (.01. am1, M2, M3, TMY and PMY are observations made in first 60 days, second 60 days, third 60 days of lactation, sum of M1, M2 and M3 and predicted 7-month milk yield, respectively. 0" 9 -I ~ -2..a 0-9 ram1 am2 em3 I I I I I I I I YEARS Figure 2. Year effects on measures of milk yield. where records were subject to culling. However, in these data there was no culling based on milk production. Yet estimates of environmental effects were biased using Model I. Thus results from Model III are presented. Year and age of cow effects from Model III are presented graphically in figures! and 2. Large fluctuations in TMY and PMY were noted for the first 4 years. For the remaining years the fluctuations were small. There was no apparent trend over time for these variables. However, M1 tended to increase and M3 tended to decrease with time. In general, TMY and PMY increased until 5 years of age with little difference from 5 to 8 years and some decline in older groups. Several reports (Drewry et al., 1959; Dawson et al., 1960; Christian et al., 1965; Melton et al., 1967; Rutledge et al., 1971) have shown similar results. The curvilinear relationship between TMY or PMY and age of cow was a result of age of cow effects on MI. While M2 and M3 increased until 4 years of age and remained constant thereafter, M1 declined sharply after 8 years of age. Todd et al. (1969) noted that young cows were less persistent than older cows, whereas Christian et al. (1965) reported that 2-year-old cows were more persistent than 3-year-olds. The cause for lower initial production by older cows is not readily discernible. Milk yields estimated via the calf suckling technique may depend on the capacity of the calf to consume milk. Results from this study (table 4) suggest that birth weight was associated (P<.01) with milk yield during early lactation (M 1 and M2) but decreased in importance in later lactation. TMY and PMY were significantly associated with birth weight. Sex.of calf did not have an important (P>.05) influence on milk yield of the dam. Heifer calves did receive slightly more milk than bull calves (table 4). Melton et al. (1967), Todd et al. (1969) and Neville et al. (1974) reported nonsignificant sex differences. However, no adjustment for differences in birth weight was made in those studies. In contrast, Rutledge et al. (1971) reported that dams nursing heifer calves produced more milk, after adjusting for differences in birth weight. Bull calves received more total milk but less milk per unit of body weight. Milk yields were more influenced by calf size than by calf sex. Phenotypic correlations among measures of milk yield, calf weights and efficiency are presented in table 5. The correlation between TMY and PMY was.99. Also the correlations of TMY and PMY with M l, M2 and M3 were similar and ranged from.69 to.79. Further, the correlations of TMY and PMY with birth weight (.18) and weaning weight (.63) were identical. The correlations of birth weight with measures of milk yield ranged from.09 to. 19, while the correlations of weaning weight with milk yield ranged from.44 to.63. Wistrand and Riggs (1966) reported a correlation of.68 between milk yield and 120-day weight. Drewry et al (1959) found correlations of. 12,.43 and.46 between calf weights and milk production during the first, third and sixth months of lactation, respectively. Christian et al. (1965) reported a correlation of.46 between weaning weight and the dam's milk production for the first 60 days of lactation and a correlation of.48

5 MILK PRODUCTION IN HEREFORDS--MEANS, CORRELATIONS 135 TABLE 5. PHENOTYPIC CORRELATIONS AMONG MEASURES OF MILK YIELD, CALF WEIGHTS AND EFFICIENCY a Birth Weaning Variable b TMY PMY wt wt Milk/gain M1.73 c M M TMY ,.38,.21 d PMY ,.36,.19 d acorrelations calculated from residuals (Model III). bm1, M2, M3, TMY and PMY are observations made in first 60 days, second 60 days, third 60 days of lactation, sum of M 1, M2 and M3 and predicted 7-month milk yield, respectively. CCorrelations >/.09 are significant at P =.01. dcorrelations with milk/gain in the three periods represented by M1, M2 and M3. between weaning weight and milk produced from 60 to 240 days. Means for milk production, average daily gain of the calf and milk/gain are shown in table 6 by stage of lactation. Milk production by month of lactation was very similar to that reported by Rutledge et al. (1971). Gifford (1953) reported milk yields in Herefords of 3.9, 3.5, 3.3, 2.8, 2.4, 2.2, 2.2 and i.9 kg for the first to the eighth month of lactation, respectively. Drewry et al. (1959) estimated milk yield of Angus cows as 6.4, 7.3 and 4.1 kg for the first, third and sixth months of lactation, respectively. Milk yields were similar for the first and second months of lactation and then declined as stage of lactation increased. On the other hand, average daily gain tended to increase. Consequently milk/gain improved. These results suggest that in order to obtain good gains in calves, supplemental feed must be provided, either in the form of grain supplement or nutritious pasture. Net energy requirements and energy available from milk are shown in table 6 also. Only during the first month was sufficient energy available from milk to meet the requirements for TABLE 6. NET ENERGY REQUIRED FOR MAINTENANCE AND GAIN VS NET ENERGY AVAILABLE FROM MILK a Month Milk Net energy needed available of intake ADG Maint Gain for gain sample (kg) (kg) Milk/gain (Mcal) (Mcal) (Mcal) anet energy for maintenance and net energy for gain required by the calves based on their respective weights and gains and those obtained from milk intake were calculated from formulae and values taken from NRC Report on Nutrient Requirements of Beef Cattle, 1970.

6 136 ROBISON, YUSUFF AND DILLARD maintenance and the realized gain, During the second to fourth months calves must receive additional energy to meet the requirements for gain. After the fourth month, milk does not supply sufficient energy to meet maintenance requirements. Thus, in these herds milk supplied less than 65% of the energy requirements after 4 months of age. Despite these values, variation in milk yield accounted for approximately 40% of the variability in weaning weight. LITERATURE CITED Christian, L.L., E.R. Hauser and A.B. Chapman Association of preweaning and postweaning traits with weaning weight in cattle. J. Anita. Sci. 24:652. Dawson, W.M., A.C. Cook and B. Knapp, Jr Milk production of beef Shorthorn cows. J. Anim. Sci. 19:502. Drewry, K.J., C.J. Brown and R.S. Honea Relationships among factors associated with mothering ability in beef cattle. J. Anim. SCI. 18:938. Gifford, W Records-of-performance tests for beef cattle in breeding herds. Milk production of dams and growth of calves. Arkansas Agr. Exp. Sta. Bull Harvey, W.R Least-squares analysis of data with unequal subclass numbers. USDA, ARS H-4. Henderson, C.R., O. Kempthorne, S.R. Searle and C.M. yon Krosigk The estimation of environmental and genetic trends from records subject to culling. Biom. 15:192. Henderson, C.R Sire evaluation and genetic trends. J.L. Lush Symposium, July, Blacksburg, VA. Knapp, B., Jr. and W.H. Black Factors influencing rate of gain in beef calves during the suckling period. J. Agri. Res. 63:249. Melton, A.A., J.K. Riggs, L.A. Nelson and T.C. Cartwright Milk production, composition and calf gains of Angus, Charolais and Hereford cows. J. Anita. Sci. 26:804. Neville, W.E., Jr., E.P. Warren and W.A. Griffey Estimates of age effects on milk production in Hereford cows. J. Anim. Sci. 38:1. Rutledge, J.J., O.W. Robison, W.T. Ahlschwede and J.E. Legates Milk yield and its influence on 205- day weight of beef calves. J. Anim. Sci. 33:563. Rutledge, J. J., O.W. Robison, W.T. Ahlschwede and J.E. Legates Estimating milk yield of beef cows. J. Anim. SCI. 34:9. Todd, J.C. and H.A. Fitzhugh, Jr Effects of breed and age of dam on milk yield and progeny growth. Texas Agri. Exp. Sta. Prog. Rep. 2689, College Station. Totusek, R. and D. Arnett Estimators of milk production in beef cows. J. Anim. Sci. 24:906. Wistrand, G.C. and J.K. Riggs Milk production of Santa Gertrudis cows measured by calf nursing and machine milking methods. J. Anim. Sci. 25:263.