EFFECT OF EARLY-SEASON SWARD MANAGEMENT ON SWARD QUALITY AND LAMB LIVEWEIGHT GAIN DURING AUTUMN

In two experiments (1990 and 1991) perennial rye-grass (cv. Talbot) pa sture was subjected to six different management treatments by adjustin g stock numbers to achieve set sward heights for set periods between t urn-out in early April and weaning in early July. The main objective o f the experiments was to measure the effect of differences in sward ma nagement up to July on subsequent sward type, and the effect of sward type on the performance of weaned lambs between mid-July and early Oct ober when all swards were grazed at a sward height of 7 cm. In Experim ent 1 swards were grazed at 7 cm initially and then reduced to 3 cm at various dates and maintained at 3 cm until early July. In Experiment 2 swards were grazed initially at 7 cm, and this was reduced to 3 cm a nd then allowed to return to 7 cm at various dates up to early July. G razing at a sward height of 7 cm up to weaning, in early July, gave me an twin lamb growth rates of 310 g d-1, while at a lower sward surface height of 3 cm lamb growth rate was reduced to 206 g d-1. The density of seed heads produced from July was strongly influenced by earlier m anagement. Grazing at 7 cm up to July gave a high density of seed head s (213m-2), and this reduced (126 m-2) by grazing to 3 cm. Seed heads were almost eliminated (17 m-2) by grazing at 7 cm until late June fol lowed by grazing down to 3 cm in early July. Reducing sward surface he ight from 7 cm to 3 cm at an earlier date tended to increase the devel opment of seed heads from early July. Where swards were grazed from 7 cm to 3 cm and then allowed to return to 7 cm, the later in the pre-we aning period this took place the greater the reduction in seed head de velopment. Greater seed head density was associated with a significant decrease in the nitrogen content of the herbage on offer in Experimen t 2, but an increase in modified acid detergent (MAD) fibre content wa s not significant. Despite the differences in the sward type on offer, the effect on weaned lamb growth rate was small. Lamb liveweight gain during autumn was significantly reduced in Experiment 2 following ear lier grazing at 7 cm compared with 3 cm, but liveweight gain differenc es in Experiment 1 were not significant.