EFFECT OF SUPPLEMENTATION ON PRODUCTION BY SPRING-CALVING DAIRY-COWS GRAZING SWARDS OF DIFFERING CLOVER CONTENT

An experiment was carried out to examine the effect of supplementation on the performance of spring-calving dairy cows grazing swards of dif fering perennial ryegrass and white clover content. Seventeen heifers and sixty-four Friesian cows in their third to ninth week of lactation were turned out onto one of three pastures with different proportions of perennial ryegrass and white clover. Nine animals on each pasture received either 0, 2 or 4 kg d-1 of a concentrate with a crude protein concentration of 180 g kg-1 dry matter (DM). Prior to grazing, swards contained proportionately 0.01 (L), 0.15 (M) and 0.20 (H) of total DM as clover. During the experiment, grazing pressures were adjusted by movement of buffer fences to maintain compressed sward heights at 6 cm . Samples taken 26 and 68 d after the start of grazing showed little c hange in the proportion of clover in sward L (< 0.01 and 0.02 respecti vely), but convergence in the proportion of clover in swards M and L ( 0.08-0.16 and 0.10-0.15 respectively). Mean daily yields of milk, fat, protein and lactose increased significantly with increased clover con tent and, even without supplementation, daily yields were 25.4, 0.98, 0.73 and 1.09 kg respectively on sward H. Of the milk components, only protein was significantly increased by increasing sward clover conten t. The response in milk yield to supplementation was greater on sward L than on swards M and H.