Effects of levels of crude protein and ground corn cobs in total mixed ration on intake, rumen fermentation and milk production in crossbred Holstein Friesian lactating dairy cows

Four, multiparous Holstein Friesian dairy crossbred cows with an initial body weight of 421.3 ± 44.3 kg and day-in-milk 62 ± 4.2 days were arranged according to a 4 × 4 Latin square design to evaluate the effect of levels of crude protein (CP) and ground corn cobs (CCs) in total mixed ration (TMR) on feed intake, rumen fermentation and milk production. The crude protein levels in TMR used in this experiment were 12%, 14%, 16% and 18% of dry matter (DM). Ground CCs and rice straw (1:1) were used as roughage sources and mixed with concentrate at 40:60 ratios. It was found that increasing CP in TMR resulted in linearly increasing voluntary DM intake (12.2, 12.7, 12.6 and 14.3 kg/d), protein intake (1.4, 1.8, 2.0 and 2.5 kg/d) and organic matter intake (11.2, 11.7, 11.6 and 13.0 kg/d). Digestion coefficients, ruminal pH and total volatile fatty acids were not different among dietary treatments (P > 0.05). However, ruminal ammonia-nitrogen and blood urea-nitrogen were increased when levels of CP in TMR increas...