PSII-14 Influence of recent postpartum weight variation on milk production, cow and calf performance and reproductive efficiency of beef cows in Southern Brazil

Abstract

Abstract The objective of this study was to evaluate the influence of the weight changes between calving to peak lactation of range beef cows on the cow and calf performance, milk production and pregnancy rate. Data were collected from 142 primiparous and multiparous beef cows, over a 5-year period. Cows and calves were raised in an extensive range system in Southern Brazil. Cows were divided into two groups according to calving performance and peak lactation. Cows that lost weight (L group, n = 59) and cows that gain weight (G group, n = 83). Milk yield evaluation (weigh-suckle-weigh technique), cow and calf performance were estimated from calving to 189 postpartum days, every 21 days. Cows were subjected to an estrus synchronization protocol and after that, breed by natural service for 45 days. Analysis of variance (ANOVA - GLM) was performed considering effects of the two groups, and pregnancy rates were compared using chi-square analysis. Calves from L cows had greater (P = 0.03) ADG between 21 and 42 days postpartum. However, there was no difference (P > 0.05) in weaning weight. Total milk production was greater (P = 0.01) in L cows. The cows from group G showed a tendency (P = 0.08) to increase pregnancy rate by 15% compared to L cows. In conclusion, cows that gain weight between calving to peak lactation have lower total milk production without any influence in calf performance, and appear to have an increase in pregnancy rate.