Effect of timing of pasture allocation on production, behavior, rumen function, and metabolism of early lactating dairy cows during autumn

The objective of the present study was to evaluate the effect of timing of pasture allocation on performance, feeding behavior, rumen function and plasma and urine metabolites of early-lactation dairy cows in autumn, strip-grazing a perennial ryegrass sward. Forty-two Holstein Friesian cows were randomly allocated to one of the following treatments: Pasture strips allocated daily at either 10:00 h (AM-ALL), 16:50 h (PM-ALL) or twice a day at 10:00 and 16:50 h (AM-PM). Herbage allowance was 21 kg DM/cow/day for all treatments. All cows received a daily allocation of concentrate and grass silage, 3.0 and 3.2 kg DM per cow, respectively. Herbage chemical composition differed amongst treatments, as dry matter and WSC contents were greater in PM-ALL than in AM-ALL and AM-PM. Milk yield tended to be greater with PM-ALL (P=0.06) compared with AM-ALL and AM-PM. The concentration of protein tended to be greater with AM-PM (P=0.09) compared with PM-ALL and AM-ALL. Protein and urea concentrations in milk did not differ among treatments. Daily grazing, ruminating and idling times were similar among treatments (P>0.05). During the first 2 h, cows in AM-ALL grazed 30 and 15 min longer than cows in AM-PM and PM-ALL treatments (P<0.05). Herbage disappearance was greater (P=0.003) in PM-ALL compared with AM-ALL and AM-PM. Treatment did not affect rumen fermentation metabolites, except for the concentration of propionic acid, which was 3% lower for cows in AM-PM compared with AM-ALL and PM-ALL cows. Cows in PM-ALL had lower concentration of urea in plasma 0.88 and 0.68 mmol/L less compared with cows in AM-ALL and AM-PM (P=0.04). Concentrations of urinary metabolites were not affected by treatment. These results suggest that timing of pasture strip allocation alters nutrients supplied by herbage to cows, but has only a small effect on herbage dry matter intake. Consequently, allocating the daily pasture strips in the afternoon would tend to increase milk production compared with allocations during the morning (~3) and twice a day (4.4%).