Composition and acceptability to sheep of twelve summer forage crops

Abstract

The composition and relative acceptability to sheep of eight forage sorghum and three forage millet cultivars were assessed in two experiments at Tamworth and Armidale, New South Wales. Millets were consistently superior to sorghums in chemical composition, in vitro digestibility and acceptability. Japanese millet (Echinochloa utilis) which had the highest mean sulphur (0.45 per cent) and sodium (0.03 per cent) contents and a very narrow nitrogen : sulphur ratio (5.7 : 1 ) , was easily the most acceptable. Its disadvantage was its very early maturity with subsequent poor regrowth. In the second experiment, two pearl millets were similar to eight sorghums in terms of dry matter production (means 2.1 vs. 2.0 t ha-1 per cut respectively) but tended to be more acceptable to the sheep and produced forage of superior quality. The eight sorghum cultivars and one maize had very low sodium (0.008-0.01 7 per cent) and sulphur (0.09-0.20 per cent) contents and nitrogen : sulphur ratios (mean 15.9 : 1 ) wider than those of the two pearl millets (13 : 1). Despite quite low cyanide potentials (mean 0.015 per cent HCN) there was a consistent negative association between the cyanide potential and acceptability in the sorghums. The low cyanide cultivar Piper was generally the most acceptable sorghum and compared favourably with the pearl millets in acceptability. The application of 20 kg S ha-1 as gypsum failed to increase significantly the sulphur content of any of the forages, but significantly reduced the nitrogen : sulphur ratio from 14.1 : 1 to 13.3 : 1 in the second year.The solution to the problem of unsatisfactory animal production on summer forages appears to lie in increasing the dry matter production per unit area of millets or the quality of sorghums.