REDUCING POSTPARTUM ANESTROUS INTERVAL IN 1ST-CALF BOS-INDICUS CROSSBRED BEEF HEIFERS .2. RESPONSES TO WEANING AND SUPPLEMENTATION

Supplementation designed to increase the supply of glucose and amino a cids, was compared with early weaning as strategies for reducing post- partum anoestrous in Bos indicus x Bos taurus (5/8 x 3/8) first-lactat ion heifers. Twenty-three pregnant heifers were allocated to four trea tment groups and fed long-chopped hay (15.8 g N/kg dry matter) ad libi tum and a complete mineral mixture throughout the experiment as well a s 450 g molasses and 50 g urea per day during the final month of pregn ancy. After calving, three groups were supplemented daily for 120 days with either 2 kg cracked rice (E), 0.4 kg formaldehyde-treated casein (P), or cracked rice (2 kg) + formaldehyde-treated casein (0-4 kg) (E + P); the unsupplemented control group had their calves weaned at 60 days post-partum. Supplemented animals had significantly higher intake s of hay (7.1-7.3 v. 5.9 kg OM/day), weight gain (0.4-0.5 v. 0.0 kg/da y) and body condition score (4.6-4.7 v. 4.3) than the unsupplemented h eifers, but there were no differences between the supplemented groups in these variables. Unsupplemented animals and heifers fed P partition ed similar amounts of lactose and fat into milk, whereas secretion of both lactose and protein was significantly higher in the E + P and E g roups. All control heifers ovulated within 14 days of their calves bei ng weaned, whereas only two of the lactating supplemented heifers (E P) showed cyclic ovarian activity at that time and three other lactat ing heifers ovulated several weeks later. The response to weaning occu rred in heifers that had a liveweight and condition score of 374 kg an d 4.3 respectively, which was 30-50 kg and a half unit in condition be low the suckling heifers. In unsupplemented heifers showing ovarian cy clicity, acetate entry rate was less than half that of the supplemente d animals, whereas glucose entry rate, adjusted for loss to lactose, w as similar for both groups. Supplementation did not affect either the basal concentration or frequency of pulsatile release of luteinizing h ormone (LH) at 60 days post-partum, or the LH response to gonadotrophi n releasing hormone (5 mug GnRH). It is concluded that under the condi tions of the present study, weaning had a greater effect than post-par tum nutritional supplements on the resumption of ovarian activity in f irst-lactation heifers with moderate nutrition.