No abstract

Cotton threads were used by Hoflund, Quin & Clark (1948) to study the rate of breakdown of cellulose in the rumen of sheep. These workers found that on a basic diet of poor quality grass hay, both cellulose breakdown and appetite were stimulated by small amounts of sugar in the diet, but markedly inhibited by excessive amounts of sugar. Excess casein suddenly introduced into a diet low in protein and carbohydrate caused a marked inhibition of cellulose digestion.When comparing between-cow differences in digestibility coefficients for crude fibre, Balch (1950) obtained data suggesting that a high ratio of water to dry matter in the total intake, and hence perhaps in the reticulo-ruminal digesta, favoured the breakdown of crude fibre. If so, it might be postulated that breakdown of the constituents of crude fibre would be lower among the dry digesta in the dorsal sac of the rumen than among the more fluid contents of the ventral sac. Confirmation of the importance of fluid conditions in determining the rate of breakdown of crude fibre in the reticulo-rumen would also offer a possible explanation for the depression of the digestibility of crude fibre known to result from the grinding of hay. Balch (1950) showed that this depression of digestibility of fibre was not the result of an accelerated rate of passage of ground hay through the reticulo-rumen.This communication is an account of studies done with two fistulated cows to check the hypothesis outlined above. The main technique used was a modification of the cotton-thread method of Hoflund et al. (1948), but the results were checked by one trial with hay suspended in the rumen in silk bags. METHODS