SUBSTITUTION EFFECTS OF FEEDING ROLLED BARLEY-GRAIN TO GRAZING DAIRY-COWS

Twenty-one Holstein Friesian cows were used in a 3 x 3 Latin square de sign 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 supplemen ted with 0, 4 or 8 kg day-1 of barley grain. Intakes of metabolisable energy (ME) and crude protein from pasture, estimated using pasture cl ipping techniques, were in excess of requirements for cows giving 201 day-1. Substitution rates were similar with both levels of grain suppl ementation and lower than predicted. Consistent with this, there were minor differences in rumen pH, rumen volatile fatty acids concentratio ns and rumen osmolality. These observations indicate that either the b arley grain was fermented slowly in the rumen or the pasture had a sig nificant buffering capacity. The yield of fat-corrected milk increased by only 0.1 kg kg-1 barley and there was a significant reduction in p lasma 3-hydroxybutyrate. These results suggest that, despite the subst antial increase in intake when barley was fed, the milking potential o f the cows was not greatly limited by ME intake, and most of the addit ional energy intake was partitioned into body tissue.