The effects of sward characteristics and supplement type on the herbage intake and milk production of summer-calving cows

High (H; 27 350 m(-2)) or low (L; 13 300 m(-2)) tiller density perennial ryegrass swards were created in the mid- and late grazing season by imposing different award heights in the spring. Summer-calving cows then grazed these swards from 6 June to 2 September 1992 and were offered 5 kg fresh weight hd(-1) d(-1) of either a barley (S) or a molassed sugar beet pulp (F) based supplement. The factorial combination of award and supplement types resulted in four experimental swards being grazed by thirteen Holstein/Friesian cows each. Supplement F contained more crude fibre (110 vs. 58 g kg(-1)) and less metabolizable energy [12.5 vs. 13.2 MJ kg(-1) dry matter (DM)] than supplement S. Herbage on the H sward contained more metabolizable energy (11.9 vs. 10.4 MJ kg(-1) DM) and crude protein (232 vs. 205 g kg(-1) DM), had fewer rejected areas (16.5 vs. 26.9%) and a higher live-dead tiller ratio (4.6 vs. 2.1) than that on the L sward. Sward, but not supplement type, significantly affected the intake of grazed herbage (P<0.001). On average, the herbage intakes of cows grazing H swards were higher than for L swards (14.5 vs. 11.6 kg DM d(-1)) and those of cows on the S and F supplements were 12.6 and 13.5 kg DM d(-1) respectively. Averaged over the grazing period, award and supplement had no significant effects on milk yield, milk composition or yield of constituents. When expressed on an average weekly basis, cows grazing an L award and offered the F supplement on occasions had significantly lower milk yields and higher milk fat contents (P<0.05) than those grazing an H sward and offered the S supplement. There were no significant effects on cow live weight or condition score change. The results suggested that grazing swards with a high density of live tillers increased herbage intakes and on occasions milk yield, relative to low density swards. However, small increases in energy intake from sward and supplement effects were used primarily to ameliorate liveweight loss.