THE EFFECTS OF SWARD HEIGHT AND CONCENTRATE SUPPLEMENTATION ON THE PERFORMANCE OF SPRING CALVING DAIRY-COWS GRAZING PERENNIAL RYEGRASS WHITE CLOVER SWARDS

Forty-eight spring-calving, Holstein-Friesian cows were continuously s tocked on perennial ryegrass-white clover swards maintained at compres sed sward heights of 4, 6 or 8 cm and offered 0 (U) or 4 (S) kg concen trates. Milk yields and composition, live weights and intakes (estimat ed by the n-alkane technique) were recorded for periods 24 May to 27 J une (P1) and 28 June to 8 August 1992 (P2) with 4 cm swards not used i n P2. Milk and component yields were significantly lower at 4 cm than at 6 or 8 cm in P1 and significantly higher when supplements were offe red in both periods with no significant interaction. Herbage intakes w ere reduced more by supplementation at lower sward heights. Live weigh t was significantly lower on the 4 cm sward. Fat concentrations were u naffected by height and supplementation in P1 but significantly increa sed by supplementation in P2. These results suggest that maintaining a sward height of 6 cm offers advantages in terms of individual animal output and output per ha compared with grazing at greater or lower swa rd heights.