Effects of different rates of liveweight change from 60 days before calving to calving on the productivity of mature Angus breeding cows

摘要

A herd of 55 Angus breeding cows aged 5#x2013;9 years were randomly allocated to two nutritional treatments 50 days before calving commenced in the herd. At this stage the cows had lost 8 of their autumn liveweight (22 April) of 470 kg to weigh an average of 443 kg. One group (HP) maintained its liveweight until 30 days before calving commenced. The second group (LP) continued to lose liveweight until 30 days before calving commenced. At this stage the HP weighed 438 kg and the LP weighed 426 kg. Both groups were then run together through calving on sufficient pasture to allow liveweight gains of 0.3#x2013;0.5 kg liveweight/day. Pre-calving nutritional treatments had no significant effect on any of the dependent variables (i.e., calf birth weight, calf liveweight at c. 20, 40, and 60 days of age, cow milk production at c. 20, 40, and 60 days after calving, and the length of the post-partum anoestrous interval). Date of calving had a significant (P 0.01) effect on calf liveweight measured at 20, 40, and 60 days of age, and the length of the post-partum anoestrous interval (-0.40 #xB1; 0.191 days/day). However, none of these variables retained a significant association with calving date when the covariance of each variable with the other dependent variables was taken into account, suggesting the presence of a common factor. By fitting cubic polynomial regression equations to records of pre-calving cow liveweight, an estimate of the liveweight change of the cow at particular times before calving was made. It was found that there was a possible relationship between calf birth weight and cow liveweight gain between 0 and 30 days before calving (r=0.23,P 0.10), but no other relationship between pre-calving liveweight change and calf liveweight or cow milk production was found. There was a significant correlation of -0.42 (P 0.01) between cow liveweight change in the period 40#x2013;60 days before calving and the length of the post-partum anoestrous interval. This relationship accounted for the significant variation in the length of the post-partum anoestrous interval previously attributed to calving date. A regression of -18.4 #xB1; 4.42 days/kg liveweight change per day was calculated. There was no relationship between the length of the post-partum anoestrous interval and cow liveweight change 0#x2013;30 days before calving.