Tropical Grasslands (1989) Volume 23, 203–210

EFFECT OF AGE OF MILLET AND SORGHUM HAYS ON THEIR COMPOSITION, DIGESTIBILITY AND INTAKE BY SHEEP

D.A. HEDGES1, J.L. WHEELER2 and D.K. MULDOON2

1CSIRO Division of Animal Production, Armidale, N.S.W., 2350
2N.S.W. Department of Agriculture Experiment Station, Trangie, N.S.W.

Abstract

A sorghum × sudan grass hybrid (Sorghum bicolor × S. sudanense cv. Sudax ST6) and Japanese barnyard millet (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 days after sowing and then chaffed. Intake, liveweight change and wool production were measured using groups of crossbred lambs fed al libitum on these hays for eight weeks. The digestibility of each hay was determined using similar lambs fed al libitum in metabolism crates.
Intake of both hay types declined with age of forage but on average 1 sheep consumed 38% more dry matter/day of millet than of sorghum hay. Liveweight change and wool production reflected a decline in digestibility and intake with age but the rate of decline in liveweight gain was much more rapid in sorghum than in millet. The data suggest that with sorghum hay, digestible organic matter intake would decrease to 280 g/day and daily liveweight gain would decline to zero when organic matter digestibility fell to approximately 60% in hay cut at 63 days. Liveweight change continued to be positive on millet hay even when cut 86 days after sowing.
For sorghum, gain per head and estimated gain per hectare were greatest for the hay cut at 53 days maturity. The utilization of sorghum as young as this in commercial practice will probably depend on the release of cultivars of unequivocally low cyanide potential.

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