Timing of feeding for dairy cows: Rumen metabolism, nutrient digestibility, nitrogen partitioning, and milk fatty acids profiles

Abstract

Timing of eating is a multiscience that mediates global animal and human physiology and metabolism. The objective was to determine effects of providing a total mixed ration (TMR) at either 0900 or 2100h on rumen fermentation and passage kinetics, microbial protein biomass, apparent total tract nutrient digestibility, nitrogen partitioning, and milk fatty acids profiles of lactating cows. Four multiparous (77±25 days in milk) and four primiparous (90±33 days in milk) Holstein cows were used in a cross-over design study with two 6-week periods. Each period had a 3-week adaptation period. The TMR had forage to concentrate ratio of 50.2:49.8 (DM based). Total fecal and urine were collected during a sampling week in each period to measure total tract nutrient digestibility and nitrogen partitioning. Urinary excretion of purine derivatives was utilized to estimate microbial protein biomass. Provision of TMR at 2100h instead of 0900h increased apparent total tract DM, CP and fiber digestibility. Rumen ammonia concentrations were lower in the 2100h fed than in the 0900h fed primiparous cows. Rumen propionate was lower and the acetate to propionate ratio was higher in 2100h-fed than in 0900h-fed multiparous cows. Microbial protein estimates and the milk proportions of total short, medium, and long chain fatty acids were not significantly different between morning and evening feed deliveries. Feeding at 2100h instead of 0900h decreased (P≤0.05) milk proportions of C10:0, C12:0, C12:1, C13:0, C13:1 and C18:3 n-3, and tended to decrease (P≤0.10) proportions of C8:0 and C18:1 trans-9, while increasing that of C18:0. Evening-fed cows tended to realize a greater rumen volume compared with morning-fed cows. Evening instead of morning feeding reduced the proportion of nitrogen that was excreted in urine and secreted in milk. Findings suggest that feed delivery at 2100h instead of 0900h can improve total tract nutrient digestibility, nitrogen dynamics, and milk energy output. Reduced N excretion by evening feeding has environmental and health implications.