Ruminant Nutrition: Calves and Heifers

Evaluations of the interaction between nutrition and reproduction of dairy heifers grazing intensively managed pasture are scarce. Thus, we aimed to evaluate performance, muscle development, oocyte quality and in vitro embryo production of grazing crossbred heifers fed increasing CP levels in the supplement. Eighteen pubertal crossbred heifers (Holstein x Gyr; initial BW of 350 ± 8.0 kg) were used in a 90-d trial. Two supplements (12 and 24% CP, S12CP and S24CP) and control treatment (mineral mixture, MM) were randomly assigned to the heifers. Three ovarium pic-up were performed. DMI and CP intake were greater for supplemented (SUP) compared with MM. SUP heifers had greater ADG (P = 0.003) and rib eye area (P = 0.04) than MM, and carcass ultrasonography indicated a trend for greater rib eye area for S24CP comparing with S12CP (Table 1). Viable oocytes were not affected by supplementation strategy. However, cleavage and blastocyst rates were negatively affected by SUP (P < 0.05), and S12CP had lower blastocyst rate than S24CP (P = 0.012; Table 1). In summary, supplementation with concentrate containing 24% CP might be an appropriate strategy for satisfactory performance during the rainy season in tropical climates. In contrast, the in vitro embryo production was impaired with supplementation.