LAUSR

Abstract Currently, there is a trend in management practices to feed a high concentrate diet to sustain a high level of milk production. The objective of this study was to identify the differences between primiparous (PP) and multiparous (MP) dairy cows fed a high-concentrate diet on feed intake and behavior, rumen pH and rumen fermentation, blood metabolites, inflammation, and milk production and efficiency. Twenty-four PP (DIM =114±20; 43.2±10.6 kg/d of milk; mean±SD) and fifty-four MP (DIM =99±30; 53.2±13.6 kg/d of milk) cows were fed a high-concentrate diet consisting of 35% forage and 65% concentrate mix. The study lasted for 24 d, which consisted of 14 d of environmental adaptation followed by 10 d of data collection. Rumen pH was measured via rumenocentesis for all cows and reticuloruminal pH was measured for a subset of animals (4 PP and 10 MP) using indwelling oral-administered sensors. The PP cows had greater sorting against long particles during the daytime, but greater sorting in favor of long particles at night. The dry matter intake (DMI) between 0 and 4 h after the morning feeding was not affected by parity, whereas PP cows had greater DMI from 4 to 6 h post-feeding and MP cows had greater DMI from 6 to 24 h post-feeding. Total 24-h intake was greater (25.1 vs. 22.4 kg/d) in MP than in PP. Rumen pH and fermentation profile were not affected by parity. Duration of rumen pH