Prediction of milk yield of 3-year-old Angus cows and the influence of maternal milk production on the postnatal growth of beef steers : a thesis presented in fulfilment of the requirements for the degree, Master of Sicnece (Animal Science), Massey University, Palmerston North, New Zealand

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Massey University
Maternal milk production influences calf weaning weight which is the major driver for economic return in a cow-calf operation. The objective of this study was to use measures of calf milk intake to estimate milk production of Angus (AA; n=43), Angus×Friesian (AF; n=32), Angus×Jersey (AJ; n=40) and Angus×Kiwi-Cross (AK; n=21) cows, and to determine how milk yield was related to calf growth rate (n=64) from birth to one year of age. Milk production was estimated by the weigh-suckle-weigh (WSW) technique at an average 32, 49, 80, 120 and 160 days (D) post-partum. Third-order Legendre polynomials were fitted to milk data using random regression to estimate the lactation curve for each cow. Live weight of all steers was recorded at birth and thereafter accompanying every WSW measurement. Postweaning live weight was recorded at an average D240, D330 and D350 of age. Growth curves for each steer were estimated by fitting third-order Legendre polynomials to live weight data using random regression. The average total milk production from D32 to D160 was 1337 ± 22 kg for AF cows, 1245 ± 20 kg for AJ cows, 1301 ± 32 kg for AK cows and 1017 ± 20 kg for Angus cows. The AF, AJ and AK cows produced more (P<0.05) milk from D32 to D160 than the AA cows. The AF cows produced more (P<0.05) milk than AJ cows, with AK cows being intermediate and not differing (P>0.05) from either AF or AJ cows. Crossbred cows produced more milk (P<0.05) at all stages of lactation when compared with straightbred AA cows. In the present study, as the proportion of Friesian or Jersey in the crossbreds increased from 0 to 50%, an extra 325 kg and 240 kg of milk, respectively, was expected compared to the AA cows. Total energy intake from milk was higher (P<0.05) for the AF-, AJ- and AK-reared steers compared to those reared by AA dams. This resulted in higher liveweight gains so that steers reared by crossbred cows were heavier (P<0.05) from D60 to D270 than those reared by AA cows. Results also revealed that the higher live weight at D60 in AJ-reared steers compared to AA-reared steers was due to differences in milk consumption from D32 to D60. The higher live weight of AF- and AK-reared steers at D60 compared to AA-reared steers was attributed to a maternal effect on steer size; however, from D90 until weaning at D160, any differences in live weight were due to differences in milk consumption. Estimation of the theoretical pasture consumption revealed that AA- reared steers compensated for the lower milk intake by eating more grass, however, this was not enough to support high daily gains during the pre-weaning period. The differences in live weight seen at weaning between steers were maintained post-weaning until D270 and were attributed to differences in milk consumption during the pre-weaning period. Under nonlimiting nutrient availability, AF, AJ and AK cows were able to pr
Milk production, Milk yield, Angus cattle, Calf growth, Weaning weight