Anzola et al., 1990. Livest. Res. Rural Dev., 2 (3): 1-9

The effect of strategic supplementation with bypass protein and fat to dual purpose cows (1/2 European; 1/2 Zebu) was studied from calving to 188 days of lactation, during the dry and beginning of the wet season in the Colombian tropics. Forty F1 cows of four breeding groups: Normandy x Zebu (N x Z = 14); Brown Swiss x Zebu (BS x Z = 10); Gyr x Holstein (G x H = 7) and Holstein x Zebu (H x Z = 9) grazing Brachiaria decumbens were supplemented with three levels of bypass protein (0, 0.5 and 1 kg dry matter per day) of Cotton Seed Meal (CSM) and a mixture of urea, sulphur and a combined source of protein, starch and oil (0.5 kg dry matter per day of rice polishing, RP); the control group grazed Brachiaria decumbens without supplements. A positive (P<0.05) effect was observed in total and daily milk production due to supplementation. Cows in all treatments lost weight but those given zero CSM had the highest weight losses (-299 g/day) (P<0.05). Calves out of supplemented cows gained faster (P<0.05) and had heavier weaning weights (P<0.05) than calves in the control group. Gyr x Holstein F1 cows had significantly (P<0.05) greater total and daily milk production. Reproductive performance was significantly (P<0.05) better in all supplemented groups compared with the control group (66.7 vs 30% pregnancy rates). Normandy x Zebu and Holstein x Zebu averaged 74.6% pregnancy rate against 34.3% for Brown Swiss x Zebu and Gyr x Holstein cows. In conclusion, supplemented cows showed better total productive performance due to lower weight losses, higher milk production, better pregnancy rate and heavier calves.