Pasture quality and ruminant nutrition

Abstract

Abstract Single variety ryegrass pastures, with or without white clover, which have consistently given different weight gains in sheep (highest to lowest: short‐rotation > Ariki > perennial rye grass) have been analysed at intervals for the various carbohydrate fractions, lignin, and total nitrogen. Italian ryegrass, included in one trial, gave weight gains similar to those for short‐rotation ryegrass, and was also analysed, as was clover, which boasted all of the grass‐only weight gains. Short‐rotation ryegrass had consistently lower cellulose and possibly higher soluble sugars than perennial ryegrass, Italian ryegrass had lower cellulose and possibly lower hemicellulose and higher soluble sugars than perennial. The carbohydrate composition of Ariki was substantially the same as that for perennial ryegrass. Pectin and water‐soluble polysaccharide were insignificant fractions in the grasses but important in the clover. There were no significant differences in lignin levels, which were always low, and only Italian differed substantially from perennial ryegrass in total nitrogen. Clover had no effect on the carbohydrate composition of the grasses but contained a higher proportion of readily fermentable carbohydrate than the grasses. It is suggested that the carbohydrate differences between shortrotation—Italian ryegrass and Ariki‐perennial ryegrass and between grass and clover can help explain the differences in animal weight gains by two mechanisms:— fermentation to different V.F.A. mixtures in the rumen; rate of breakdown, and hence rate of passage, of ingested grass to small particles which can pass out of the rumen.