AGE OF COW AND AGE OF DAM EFFECTS ON MILK PRODUCTION OF HEREFORD COWS 1. ABSTRACt"

Size: px
Start display at page:

Download "AGE OF COW AND AGE OF DAM EFFECTS ON MILK PRODUCTION OF HEREFORD COWS 1. ABSTRACt""

Transcription

1 AGE OF COW AND AGE OF DAM EFFECTS ON MILK PRODUCTION OF HEREFORD COWS 1 D. L. Lubritz 2, K. Forrest 2 and O. W. Robison 2 North Carolina State University, Raleigh ABSTRACt" Milk production in Hereford cows was studied utilizing 2,487 lactation records on 926 cows. Data were collected over 17 yr (1968 to 1984) from two related herds. Estimates of daily milk yield were obtained at bimonthly intervals by the calf suckling technique. The sum of three monthly measures (TMY), a predicted sum of seven monthly observations (PMY) and 25-d weight of the calf were studied. Year, age of cow, age of dam at cow's birth and calf birth weight affected (P <.5) all traits. Birth weight affected all measures of milk, with heavier calves obtaining more milk. Age of cow effects were significantly curvilinear, with PMY and TMY increasing for cows from 2 to 5 yr of age, but not differing for cows 6 yr and older. Age of cow effects on 25-d weight were similar to those for milk. As age of cow increased from 2 to 4 yr, 25-d calf weight increased. A leveling off in 25-d weight was observed for calves of cows 5 yr and older. Effects of age of dam of cow also were significant for all milk Waits studied. As age of dam increased, PMY and TMY decreased. Highest milk yields were for cows born to and reared by 2-yr-old dams, intermediate milk yields for those by 3- and 4-yr-old dams and lowest yields by daughters of mature dams. Cows born to and reared by older dams produced less milk and weaned lighter calves. There were no interactions between age of cow and age of dam. This suggests a lasting detrimental effect of older cows on lactation yield of daughters. Thus, it appears that age of dam should be considered in evaluation of cow performance. (Key Words: Cows, Age, Dams, Milk Yield, Beef Cattle, Weaning Weight.) J. Anita. Sci : Introduction Calf weaning weights largely determine net income of many beef producers. Milk supply has been shown to be the single most important component affecting weaning weight (Knapp and Black, 1941; Rutledge et al., 1971). Estimates of the variation in weaning weight accounted for by milk volume range from 2 to 6% (Robison et al., 1978). Thus it is important to characterize lactational performance of beef cows. To maximize milk yields 1paper no of the Journal series of The North Carolina ARS, Raleigh, Dept. of Anim. Sci. Received October 13, Accepted February 27, and weaning weight, improved genetic potential for calf growth should be supported by an improved environment. The significant influence of milk volume on weaning weight substantiates a need to characterize the lactational performance of beef cows. Two methods of estimating milk production are calf suckling and hand milking after oxytocin injection. Rutledge et al. (1972) determined that samples taken at 56-d intervals were sufficient to estimate milk yield accurately. Objectives of this study were to evaluate age of cow and age of the cow's dam when she was born on her subsequent milk yield and 25-d weight of her calves. It has been proposed by Mangus and Brinks (1971), Koch (1972) and Vesely and Robison (1972) that superior weaning weights of heifers lead to 2544

2 AGE OF COW AND DAM EFFECTS ON MILK PRODUCTION 2545 TABLE 1. HERD MEANS AND STANDARD DEVIATIONS FOR PMY, TMY AND 25-D WEIGHT (kg) Trait a Mean SD No. Mean SD No. Mean SD No. PMY, kg/'/d ,487 TMY, kg/3 d , d wt ,487 atmy is the sum of three 24-h milk production estimates and PMY is the predicted sum of seven 24-h milk estimates. subsequent poor performance as dams. Because age of cow is known to affect weaning weight, this study was undertaken to examine the influence of age of a heifer's dam on her subsequent performance as a cow. Materials and Methods Data used in this study were from two related herds of Hereford cattle. There were 2,487 lactation records on 926 cows. Data were collected from 1968 to Eight or nine service sires were used each year. Bulls were used only 1 yr, and in both herds. Service sires used the final 14 yr were selected for weaning weight, postweaning gain or randomly. Cows born after 1971 would have selected bulls as sires. All heifer calves were put in the breeding herd to calve at 2 yr of age. If they did not calve at 2, they were given a second opportunity at 3 yr of age. Cows open over 3 yr of age were culled. Decisions of cull were based only on failure to breed. Cows and calves were maintained on pasture with silage and protein supplement provided during winter months. Supplemental feeding corresponded with the first 9 d of the calving season. Creep feeding was not em- ployed and bull calves were not castrated. Milk production was estimated at 56-d intervals by the calf suckling technique. Three measurements were obtained during each lactation. The sum of these three measures is called total milk yield (TMY) and has units of kg/3 d. Predicted 7-mo milk yield over the total lactation, PMY, was estimated according to procedures of Rutledge et al. (1972) and has units of kg/7 d. Briefly, cows and calves were separated at 8; at 16 calves were weighed, allowed to nurse and, after completion of nursing (15 to 2 min), were reweighed. Cows and calves then were separated overnight. The next morning at 8 the calves were weighed, allowed to nurse and reweighed. The sum of the differences between the two posmursing and prenursing weights represents 24-h milk yield. Data were analyzed according to maximum likelihood procedures outlined by Harvey (1975). The following model was used to analyze 25-d weight, PMY and TMY: Yijklmn = M + A i + Bj + Ck + DI + Em + b(xijklmn - Xijklm) + eijklmn where TABLE 2. MAXIMUM LIKELIHOOD CONSTANTS AND STANDARD ERRORS FOR AGE OF COW EFFECTS ON PREDICTED MILK YIELD (kg/7 d) , , ,

3 2546 LUBRITZ ET AL. TABLE 3. MAXIMUM LIKELIHOOD CONSTANTS AND STANDARD ERRORS FOR AGE OF COW EFFECTS ON TOTAL MILK YIELD (kg/3 d) Yij- = the individual observation for a klmn given dependent variable, M = overall mean, Ai = random effect of the i th cow. Bj= fixed effect of the jth year, k fixed effect of the k th sex of calf, D1 = fixed effect of I th age of cow, E m fixed effect of the m th age of dam when the cow was born, b = partial regression coefficient, Xijklmn = birth weight of calf and eijklm n -- random error associated with Y. Repeatabilities of.43 for PMY and TMY and.3 for 25-d weight were used. Age of cow x age of dam interactions were not significant and were deleted from the model. Results and Discussion Means and standard deviations for the waits are presented in Table 1. All main effects were significant for PMY, TMY and 25-d weight, with the exception that sex of calf did not affect (P >.5) PMY or TMY. Maximum likelihood constants and standard errors for PMY by age of cow are shown in Table 2. Maximum likelihood constants for PMY increased from 2 to 5 yr of age and did not differ from 6 to 1 yr. Although age effects appear to be somewhat larger for herd 2, the trends across ages were similar. Similar results were observed for TMY (Table 3). Previous work estimated phenotypic and genotypic correlations of.99 and 1., respectively, between TMY and PMY (Dillard et al., 1978; Robison et al., 1978). Age of cow effects on 25-d weight followed trends similar to those for milk. Maximum likelihood constants increased from 2 to 5 yr of age but did not change from 6 to 1 yr (Table 4). Results presented in Tables 2, 3 and 4 agree with generally accepted effects of age of cow on milk yield and weaning weight. Age of dam of cow effects were significant for all traits. These results suggest that cows TABLE 4. MAXIMUM LIKELIHOOD CONSTANTS AND STANDARD ERRORS FOR AGE OF COW EFFECTS ON 25-D CALF WEIGHT (kg)

4 AGE OF COW AND DAM EFFECTS ON MILK PRODUCTION 2547 TABLE 5. MAXIMUM LIKELIHOOD CONSTANTS AND STANDARD ERRORS FOR AGE OF DAM EFFECTS ON PREDICTED MILK YIELD (kg/7 d) TABLE 6. MAXIMUM LIKELIHOOD CONSTANTS AND STANDARD ERRORS FOR AGE OF DAM EFFECTS ON TOTAL MILK YIELD (kg/3 d) born to and reared by young dams produce more milk (PMY, TMY) and rear calves with superior weaning weights. These results are among the first to confirm the speculation of earlier studies (Mangus and Brinks, 1971; Koch, 1972; Vesely and Robison, 1972) that mature, higher milking dams may be detrimental to the future performance of their female progeny. Tables 5 and 6 show age of darn effects on PMY and TMY, respectively, In general, as age of dam of the cow increased, milk production of the cow decreased. This is further illuslrated in Figure 1. Cows born to and reared by 2-yr-old dams had higher than average production, whereas cows from 3- and 4-yr-old dams were average and cows from older dams tended to have reduced milk production. TABLE 7. MAXIMUM LIKELIHOOD CONSTANTS AND STANDARD ERRORS FOR AGE OF DAM EFFECTS ON 25-D WEIGHT (kg)

5 2548 LUBRITZ ET AL. ~ "\ /o~o~o~~ & A / / -- PMY BY AGE OF COW 9 9 PaY BY AGE OF DAM A--ATIdY BY AGE OF COW &--A TMY BY AGE OF DAM -1i Q t, t,, ~, AGE Figure 1. Effects of age of cow and age of dam on difference in milk production (kg) over 3 d (TMY) or 7 d 1-1 ~~~ I.. / e~ O~O~O O~o~o/ 9 / D W] BY AGE OF COW t--i 25-D WT BY AGE OF DAM I I t I I I I I I AGE Figure 2. Effects of age of cow and age of dam on 25<1 weight (kg). Age of dam effects on 25<! weight suggest that cows from younger dams (2- and 3-yr-olds) would wean heavier calves than cows from older dams (Table 7). Figure 2 illustrates the age of dam trend in 25<1 weight. Irgang et al. (1985a,b) estimated environmental and genetic time trends in these herds. For weaning weight, environmental trends were significant (-1.12 and kg/yr), whereas the genetic trend was not significant in the weaning weight line (.1 to 1.7 kg/yr) but was significant in the gain line (.71 to 1.36 kg/yr). In contrast, the environmental trend was not significant for PMY (-.13 to -.17 kg/ yr), but the genetic trend was significant (.17 to.27 kg/yr). The model used for analyses in this paper would account for most or all of the genetic trend. In any case, the estimated genetic trend was not sufficient to explain the results obtained. Furthermore, because there was no culling of cows on performance, if genetic trend were responsible, differences among older ages should be similar to differences TABLE 8. REGRESSIONS OF TMY, PMY, AND 25- DAY WEIGHT ON BIRTH WEIGHT Trait a TMY.13".16".15" PMY 25-d wt..3* 1.94".34* 1.79".32" 1.85" atmy is the sum of three 24-h milk production estimates and PMY is the predicted sum of seven 24-h milk estimates. *P <.1. among younger ages. Such was not the case. Therefore, one must conclude that age of a cow's dam influences her production as a mother. Partial linear regression coefficients of TMY, PMY and 25<1 weight on birth weight were positive. It is not clear whether the same physiological system that results in heavier birth weights also causes cows to produce more milk and wean heavier calves or whether heavier calves create a demand for more milk and the cows respond to this stimulus (Table 8). However, the nonsignificance of sex effects on milk would suggest that the former is a more likely explanation, because male calves were heavier than female calves and yet didn't stimulate an increase in milk production. The results herein lead to the conclusion that age of dam of cow should be considered when interpreting experimental results. Further evaluation procedures must include these effects when selection decisions are made either for cows or for potential replacement heifers. Because age of cow x age of dam interactions were nonsignificant, it was concluded that superior maternal performance of older cows has a lasting detrimental influence on the productivity of their heifer calves and is reflected as a grandmaternal environmental influence on calf weaning weight. Literature Cited Dillard, E. U., M.K.M. Yusuff and O. W. Robison Milk production in Hereford cows II. Heritabflities and repeatabilities. J. Anim. Sci. 47:137. Harvey, W. R Least-squares analysis of data with unequal subclass numbers. USDA, ARS H-4.

6 AGE OF COW AND DAM EFFECTS ON MILK PRODUCTION lrgang, R., E. U. Dillard, M. W. Tess and O. W. Robison. 1985a. Selection for weaning weight and postweaning gain in Hereford cattle. U. Response to selection. J. Anita. Sci. 6:1142. h-gang, R., E. U. Dillard, M. W. Tess and O. W. Robison. 1985b. Selection for weaning weight and postweaning gain in Hereford cattle. IH. Correlated responses to selection in milk yield, preweaning and postweaning traits. J. Anita. Sci. 6:1156. Knapp, B., Jr. and W. H. Black Factors influencing rate of gain in beef calves during the suckling period. J. Agric. Res. 63:249. Koch, R. M The role of maternal effects in animal breeding: VI. Maternal effects in beef cattle. J. Anita. Sci. 35:1316. Mangus, W. L. and J. S. Brinks Relationships between direct and maternal effects on growth in Herefords. I. Environmental factors during preweaning growth. J. Anita. Sci. 32:17. Robison, O. W., M.K.M. Yusuff and E. U. DillarcL Milk production in Hereford cows. 1. Means and correlations. J. Anita. Sci. 47:131. Rutledge, J. J., O. W. Robison, W. T. Ahlschwede and J. E. Legates Milk yield and its influence on 25-day weight of beef calves. J. Anita. Sci. 33:563. Rmledge, J. J., O. W. Robison, W. T. Ahlscbwede and J. E. Legates Estimating milk yield of beef cows. J. Anita. Sci. 34:9. Veseley, J. A. and O. W. Robison Empirical selection indexes for beef cattle. J. Anita. Sci. 34:549.