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Abstract
The feeding value of Aries HD perennial ryegrass (Lolium perenne) was evaluated over summer (2 Dec 1996 to 12 March 1997) using Romney weaned lambs, with Yatsyn 1 perennial ryegrass as the control cultivar. There were three replicate plots of each cultivar of 0.33 ha continuously stocked with 8 lambs per plot to maintain a mean sward surface height of 6 cm. There was no significant difference in lamb liveweight gain (116 versus 111 ± 5.1 g day−1, P > 0.6) or herbage intake (0.7 versus 0.6 ± 0.10 kg OM day−1, P > 0.5) between Aries HD and Yatsyn 1 lambs. Liveweight gain of lambs (mean of two treatments) decreased as the experiment progressed from 174 g day−1 in December, to 102 g day−1 in January/February, to 76 g day−1 in February/March. Incidence of ryegrass staggers was low with 9% of Yatsyn 1 lambs being affected over late February/early March, which coincided with a peak lolitrem B concentration of 1.37 ppm in Yatsyn 1 pasture, which was similar between cultivars. There was no significant difference in final carcass weight of lambs grazing Aries HD and Yatsyn 1 (14.9 versus 14.6 ± 0.24 kg, P > 0.5), reflecting the similar nutritive value and alkaloid concentrations of the two cultivars over this summer/autumn period.