Chemical processing of wheat straw and cotton by-products for fattening cattle 3. Performance of animals receiving material in complete feeds

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Abstract
The fibrous roughages, wheat straw (WS) and cotton stalks (CS), were left untreated or treated with 30 g sodium hydroxide per kg, and residual alkali was either neutralized with sulphuric acid or left unneutralized. All roughages were pelleted and used either in complete feeds or separately. The effects of these treatments on the nutritive value of the roughages were examined in digestibility trials in vitro and in vivo, and in a 7·month feeding trial of a factorial arrangement of 2 × 3 × 2, in which the roughages constituted 350 g/kg of the diets. Approximately 150 g/kg of the neutral-detergent fibre (cell wall) constituents of both roughages was solubilized by sodium hydroxide treatment, while the changes in acid-detergent fibre components (cellulose and lignin) were much smaller, although evident.In vitro-dry matter digestibility of wheat straw was 22 % higher than that of cotton stalks, and its increase due to NaOH treatment was 50% and 30% for wheat straw and cotton stalks, respectively. In vivo digestibility of organic matter of wheat straw was increased from 0·47 to 0·59, and that of cotton stalks from 032 to 037. The increase was evident in all components except protein, in which digestibility was reduced. The increase in the metabolizable energy values of wheat straw from 6·86 to 7·45MJ/kg dry matter and that of cotton stalks from 4·77 to 5·10MJ/kg dry matter following sodium hydroxide treatment was not reflected in daily live-weight or carcass-weight gain in the feeding trial. The animals offered NaOH-treated roughages had significantly more fat trim, and more fat in the large depots. Including roughages in complete feeds revealed no advantage in metabolizable energy conversion into live weight.