| Popis: |
This study examined the hypothesis that partitioning of nutrients towards maternal tissue growth, rather than milk production, may favour a more rapid return to cyclic ovarian activity in lactating Brahman cows. Three strategies to decrease milk production in well-fed cows were tested. Continuous infusion of the somatostatin analogue RC-121 and immunization of cows against growth hormone releasing hormone had no significant effects on milk yield, cow and calf weight change and the duration of the period of anoestrus post-calving. Restriction of udder capacity by surgical occlusion of two teats reduced milk yield by about 20% (P < 0.001). During the first 6 weeks of lactation, cows with restricted udder capacity gained 0.31 kg/day compared with a loss of 0.08 kg/day by controls (P < 0.05). From weeks 7-20, both groups gained at 0.4 kg/day. The duration of the period of anoestrus after calving was approximately 6 months in each group. In experiments in which calves were weaned, all cows returned to ovarian activity within 16 days of weaning. It was concluded that purebred Brahmans preferentially partition nutrients towards the mammary gland and that partially redirecting nutrients towards maternal tissue growth rather than milk secretion did not result in a more rapid return to cyclic ovarian activity. |
