Energy balance, milk production and reproduction in grazing crossbred cows in the tropics with and without cereal supplementation

This study was designed to evaluate the role of supplementation with a cereal-based concentrate on energy balance, milk production and reproduction of suckling crossbred cows, grazing star grass in the tropics. Forty-eight Holstein × Zebu cows were used in a 2 × 2 factorial design from calving to 98 days post-partum. Treatment factors were diet (Control vs. Supplemented) and season of calving (dry vs. rainy). The supplement consisted of sorghum (69%), soya bean meal (14%), wheat bran (15%) and minerals (2%), contained 878 g/kg dry matter (DM), 168 g/kg DM crude protein (CP) and 11.8 MJ/kg DM metabolisable energy (ME), and was offered at 0.9% of live weight. There was no interaction between diet and season. Supplementation increased (P < 0.001) intakes of DM, ME and CP, and increased milk yield by 30% (P < 0.001). Supplementation eliminated negative energy balance (NEB) on day 21 post-calving (3.3 vs. − 22.9 MJ/day) and on day 84 post-calving (1.1 vs. − 12.1 MJ/day). The proportion of cows that showed oestrus was higher (P = 0.025) for Supplemented cows (74%), compared with Control cows (39%) and the proportion of cows that ovulated tended to be greater (P = 0.073) for Supplemented (58%) than for Control (30%) cows. Supplemented cows had a greater (P = 0.003) population of large ovarian follicles (0.6 vs. 0.3), shorter (P = 0.025) calving to first oestrus interval (62.8 ± 6.9 days vs. 68.2 ± 3.8 days) and tended to have (P = 0.079) a higher pregnancy rate at 90 days (47% vs. 22%). It is concluded that grazing crossbred cows in the tropics may experience a period of NEB post-partum, which can be reduced using cereal-based concentrates, whilst improving milk production and reproductive performance.