Herbage intake and milk yield of dairy cows grazing perennial ryegrass swards or white clover/perennial ryegrass swards at low- and medium-herbage allowances

Including legumes in grass swards generally increases nutrient intake and performance of grazing cattle. The objective of this study was to determine if the difference in herbage intake of dairy cows grazing either perennial ryegrass swards (PRG) or white clover/perennial ryegrass swards (GC) is a function of herbage allowance. Both sward types were compared at 20 or 35 kg DM/cow/day offered at ground level according to a 4 × 4 Latin square design with four 10-day periods and with 24 Holstein cows in mid-lactation. Clover represented on average 270 g/kg of live DM material in GC swards. Pre-grazing herbage mass at ground level did not differ between sward types but pre-grazing herbage mass above 5 cm and sward height was much lower on GC than on PRG swards. There was no interaction between sward type and herbage allowance on herbage intake and milk yield. Cows grazing on GC swards had lower herbage intake (−0.7 kg OM/day), OM digestibility of the selected herbage (−20 g/kg OM) and milk yield (−1.3 kg/day) than cows grazing on PRG swards. Milk fat content was unaffected by sward type and milk protein content was lower on GC than on PRG swards. Herbage intake, herbage OM digestibility, milk yield and milk protein content increased, and milk fat content decreased, with increasing herbage allowance. It is concluded that including white clover in perennial ryegrass swards, along with suppressing nitrogen fertilisation, did not improve herbage intake or milk production when this is associated with a sharp decrease in sward height and herbage mass in the upper strata of the sward.