A NOTE ON THE EFFECTS OF PATTERN OF FOOD-INTAKE AND BODY CONDITION ON THE DURATION OF THE POSTPARTUM ANESTROUS PERIOD AND LH PROFILES IN BEEF-COWS

An experiment was conducted to determine the effect of level and pattern of food intake in post-partum beef cows on the length of the post-partum anoestrous period and associated luteinizing hormone profiles. Forty-six multiparous cows were allocated at calving to one of three feeding regimes: 55 MJ metabolizable energy (ME) per day throughout (LL), 145 MJ ME per day throughout (HH), or 55 MJ ME per day until 6 weeks post partum and then 145 MJ ME per day thereafter (LH). The duration of the post-partum anoestrous period was assessed from plasma progesterone profiles. Luteinizing hormone profiles in the peripheral circulation were determined at weeks 3, 6, 8 and 11 post partum from samples collected every 20 min for 10 h. Feeding regime had no effect on either the length of the post-partum anoestrous period, being 99, 89 and 91 (s.e.d. 12.2) days for the LL, LH and HH cows respectively, or on any aspect of luteinizing hormone pulsatility. Body condition at calving was negatively correlated with the duration of the post-partum anoestrous period, each unit increase in body condition at calving being associated with a decrease in the post-partum anoestrous period of 86 (s.e. 21.8) days. Luteinizing hormone pulse frequency at 6 weeks post partum was positively correlated with body condition at calving. This experiment confirms the importance of body condition at calving in influencing the duration of the post-partum anoestrous period and indicates that level and pattern of feeding post partum has little effect when cows calve at a body condition of approximately 2.25.