Reducing post-partum anoestrous interval in first-calf Bos indicus crossbred beef heifers. 1. Effects of pre- and post-partum supplementation strategies

摘要

The effects of pre-and post-partum (ppp) v. post-partum (pp ) supplementation on reproductive function were compared in Bos indicus x Bos taurus (5/8 x 3/8) first-calf heifers. Twenty-four pregnant heifers were allocated to three treatment groups all fed roughage hay ad libitum. The dietary treatments were: (1) nil supplement controls, (2) cracked maize (1 kg) plus formaldehyde treated sunflower seed meal (0.5 kg) daily for 60 days post-partum, (3) supplement 2 from 1-2 months pre-partum to 60 days post-partum. Supplementation did not affect hay intake prior to calving (6.5 kg/day), but significantly increased (P < 0.05) intake by approximately 50% after calving compared with a 20% increase in the controls. Maternal liveweight, adjusted for the weight of the foetus and gravid uterus, was 345 kg in all groups at 5 weeks before calving. This weight declined by 6 kg in unsupplemented animals and increased by 16 kg with supplementation before calving. During the 2 months after calving, ppp supplemented animals maintained weight, pp supplemented heifers gained 26 kg, and controls lost 39 kg. Birth weight of calves from heifers supplemented before parturition was 34.2 ¦ 1.9 kg, 5.6 kg heavier than the other calves (28.64¦0.7 kg). Milk yield and N secretion tended to be highest in ppp supplemented heifers in the peri-partum period. Two months after calving, milk yield and secretion of N, fat and lactose were not different in both supplemented groups, but were significantly higher (P < 0.05) than in the controls. Endogenous pulsatile release of LH and FSH was not detected in heifers from any group 50 days after calving. Following GnRH injection (100 8g, i/m), the LH response was not significantly different between groups, but the unsupplemented animals had greater ( P < 0.05) FSH responses than the supplemented heifers. Supplemented heifers had lower ( P = 0.07) plasma GH concentrations prior to calving; after calving, GH levels were in the order: ppp supplemented < pp supplemented < controls. There was no indication that supplementation affected ovarian folliculogenesis in animals treated with exogenous gonadotrophin, and all animals were in an anoestrous state at 60 days post-partum. In conclusion, the type of supplementation practiced here did not appear to improve reproductive performance in first-calf heifers weighing 340-360 kg in early lactation. However, ppp supplementation was the most effective treatment in reducing GH levels and maintaining liveweight in the peri-natal period, both of which have been associated previously with reducing post-partum anoestrous interval.