Feeding behaviors, metabolism, and performance of primiparous and multiparous dairy cows fed high-concentrate diets

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 < 5.8 measured 750 and 570 +/- 231 min/d for PP and MP cows, respectively, which indicates that cows experienced rumen acidosis with respective coefficients of variation measuring approximately 8.2% and 10.8%, respectively. Primiparous cows produced less milk (-6.3 kg/d), 3.5% fat corrected milk (-4.2 kg/d), milk protein (-0.160 kg/d), and lactose (-0.230 kg/d). The PP cows, despite lower production, had greater concentrations in plasma of cholesterol, beta-hydroxy-butyrate (BHBA), and blood urea nitrogen and a trend for greater triglyceride than MP cows. Primiparous cows also had lower feed efficiency compared with MP (1.88 vs. 2.03). We conclude from these results that under conditions of the present study, PP dairy cows responded with lower feed efficiency and greater concentration of cholesterol, BHBA, and urea nitrogen in the blood.