Substitution effects of feeding rolled barley grain to grazing dairy cows

Abstract

Twenty-one Holstein Friesian cows were used in a 3 × 3 Latin square design to determine effects of barley supplementation on pasture intake, rumen fermentation and milk production. Cows were grazed on perennial ryegrass-white clover pasture and allocated to three groups supplemented with 0, 4 or 8 kg day −1 of barley grain. Intakes of metabolisable energy (ME) and crude protein from pasture, estimated using pasture clipping techniques, were in excess of requirements for cows giving 20 1 day −1. Substitution rates were similar with both levels of grain supplementation and lower than predicted. Consistent with this, there were minor differences in rumen pH, rumen volatile fatty acids concentrations and rumen osmolality. These observations indicate that either the barley grain was fermented slowly in the rumen or the pasture had a significant buffering capacity. The yield of fat-corrected milk increased by only 0.1 kg kg −1 barley and there was a significant reduction in plasma 3-hydroxybutyrate. These results suggest that, despite the substantial increase in intake when barley was fed, the milking potential of the cows was not greatly limited by ME intake, and most of the additional energy intake was partitioned into body tissue.