Performance, carcass quality and blood metabolites of Holstein bulls on feedlot feeding of different proportions of barley grain to maize grain

This experiment was conducted to study the effects of five different ratios of barley grain to maize grain: 1) 100:00, 2) 75:25, 3) 50:50, 4) 25:75, and 5) 00:100 on feedlot performance, carcass quality, ruminal and blood parameters of twenty-five Holstein bulls. Quadratic effects were detected for carcass efficiency and were greatest for diets with barley grain-to-maize grain ratios of 75:25 and 50:50 compared with other diets. Also, back-fat thickness, abdominal fat, and meat ether extract increased as the proportion of maize increased in the diets (P<0.05). When the proportion of maize in diets increased, the amount of undigested grain in feces increased linearly (P<0.05). At 3 and 6 h after feeding, as the proportion of barley increased in the diets, ruminal pH decreased quadratically. We conclude that feeding bulls diets based on 50:50 and 75:25 barley-to-maize grain ratios resulted in higher carcass efficiency and optimal ruminal parameters.