EFFECTS OF BODY CONDITION AT CALVING AND FEEDING LEVEL AFTER CALVING ON LH PROFILES AND THE DURATION OF THE POSTPARTUM ANESTROUS PERIOD IN BEEF-COWS

An experiment was conducted to examine the effects of body condition at calving and feeding level post partum on the duration of the post-partum anoestrous period in beef cows. Forty-seven cows were used in each of 2 years. Cows were fed differentially before calving to achieve two levels of body condition at calving in November and December and were then fed at one of two levels of feeding post partum in a 2 X 2 factorial experiment. At calving, mean body condition scores were 2.85 (F) and 2-23 (T) (P < 0.001) while live weights were 521 kg and 457 kg (P < 0.001) for F and T cows respectively. After calving metabolizable energy intakes were 111 and 118 MJ/day (H) or 56 and 64 Mj/day (L) in years 1 and 2 respectively. The H cows maintained live weight during the first 61 days of lactation while the L cows lost live weight (0.0 v. -1.1 kg/day, P < 0.001). The number of cows still acyclic on 1 May each year was higher (P < 0.01) on the TL treatment (10/24) compared with the other treatment combinations (FH: 2122; FL: 5122; TH: 2124). The effect of level of feeding on the duration of the anoestrous period was significant in the T cows (89 v. 116 days for TH and TL cows respectively; P < 0-01) but not in the F cows (80 v. 89 days for the FH and FL cows respectively; P > 0.05). At 3 weeks post partum LH pulse frequency was higher in F than in T cows and tended to be higher in H than in L cows. At 6 and 9 weeks post partum LH pulse frequency was higher in H than L cows. LH pulse amplitude was higher in F than T cows at 3 weeks post partum and tended to be higher at 6 weeks post partum. It is concluded that both body condition at calving and feeding level after calving influence the duration of the post-partum anoestrous period with the effect of feeding level being particularly pronounced in thin cows.