Abstract 87

Hedges,-DA; Wheeler,-JL; Muldoon,-DK

CSIRO Division of Animal Production, Armidale 2350, NSW, Australia.

Tropical-Grasslands. 1989, 23: 4, 203-210; 19 ref.

Sorghum bicolor X S. sudanense cv. Sudax ST6 and Echinochloa utilis cv. Shirohie were grown under irrigation on a saline clay soil. Forage was cut and made into hay 49, 53, 70, 81 and 86 d after sowing and then chaffed. Intake, liveweight changes and wool production were measured using groups of crossbred lambs fed ad lib on these hays for 8 weeks. The digestibility of each hay was determined using similar lambs fed ad lib in metabolism crates. Intake of both hay types declined with forage age but on average sheep consumed 38% more DM/d of E. utilis than of S. bicolor X S. sudanense hay. Liveweight change and wool production reflected a decline in digestibility and intake with age; the rate of decline in liveweight gain was much more rapid in S. bicolor X S. sudanense than in E. utilis. The data suggested that with S. bicolor X S. sudanense hay, digestible OM intake would decrease to 280 g/d and daily liveweight gain would decline to zero when OM digestibility fell to approx. 60% in hay cut at 63 d. Liveweight change continued to be positive on E. utilis hay even when cut 86 d after sowing. For S. bicolor X S. sudanense, liveweight gain per head and estimated gain/ha were greatest for the hay cut at 53 d maturity. It was suggested that commercial use of such young S. bicolor X S. sudanense would probably depend on the release of cultivars of unequivocally low cyanide potential.