Milk production and postpartum performance of Hereford cows in different reproduction conditions in a range breeding system.

摘要

Milk production and postpartum performance of 52 multiparous Hereford cows, with the same body condition score (3 in a 1 to 5 scale), pregnant (45) or not pregnant (24), were studied using 69 lactations between 2000 (42) and 2001 (27). Estimates of milk yield were obtained at six intervals (three 21 days and three 42 days) by the weigh-suckle-weigh technique from birth to weaning (189 days). Studied parameters included year of birth, pregnancy, calf sex and sire breed. None of the studied parameters affected (P>0.05) the milk production parameters: daily milk production, total milk yield, lactation peak and lactation duration. The body weight at calving of cows was greater (P<0.05) in 2001 (417.49+or-6.94 kg) than in 2000 (353.97+or-5.57 kg) and was not affected by the other parameters. The body weights at conception (99 days; 432.10+or-5.78 and 399.37+or-7.92 kg) and weaning (189 days; 433.30+or-6.36 and 393.46+or-8.70 kg) were greater (P>0.05) in pregnant cows than in non-pregnant animals. Sex of calf had a significant effect (P<0.05) on calf birth weight (41.75+or-1.21 kg and 37.6+or-1.13 kg for males and females, respectively). All studied parameters significantly affected calf weaning weight (P<0.05). Pregnant cows had heavier calves at weaning (194.22+or-3.41 kg) than non-pregnant cows (177.43+or-4.67 kg). The superior performance of the pregnant beef cows with similar milk yield and body condition score from calving to weaning can be explained by their better adaptation characteristics.