Effect of treatment with sodium hydroxide on the feeding value of oat and rape straw for sheep

Abstract

Oat and rape straws were treated with NaOH (70 and 40 g kg-1, respectively) by spraying with NaOH solutions (20 or 12.5% w/w), consolidating the sprayed straw into stacks, and storing under plastic. After storage for up to 60 weeks, in vitro digestibilities had been approximately doubled, although it appeared that the reaction was complete by 4 weeks. Potential digestibility of straw organic matter estimated by a polyester bag technique, was increased by c. 0.1 by NaOH treatment but the rate of digestion in the rumen was not changed. Following storage, treated and untreated straws were dried, ground, mixed with supplements and pelleted for feeding to sheep. Mixtures of treated or untreated oat straw, minerals, c. 3% urea and 0, 14, 28 or 42% starch were fed to mature wethers. The main effects of NaOH treatment of straw were to increase water intake, digestibilities of organic matter and cellulose, and rumen volatile fatty acid levels, and decrease rumen ammonia levels. Low intakes of NaOH-straw with no added starch were associated with high rumen pH (> 7.5 , probably due to unreacted alkali (equivalent to 23 g NaOH kg-1). Inclusion of starch, but not NaOH-straw treatment, improved dietary N utilization, although mean N balances were negative (- 5.5 to - 0.1 g day-1) on all diets. Feeding treated straw increased the amounts of Na eaten, and of Na and P apparently absorbed; the extra absorption was accounted for by increased urinary excretion so that retention was not increased. When diets of rape straw supplemented with urea and minerals were fed to 2-year-old wethers, NaOH treatment of straw increased intakes of food and water, organic matter digestibility, rumen volatile fatty acid concentration and N balance.