DIGESTION OF PASTURE PLANTS BY SHEEP .4. DIGESTION OF PHALARISTUBEROSA AT DIFFERENT STAGES OF MATURITY

A study was made of the composition, intake, and digestion of dried Phalaris tuberosa forage that had been harvested at three stages of maturity. Advancing maturity was associated with: (i) decreased food intake; (ii) increased expenditure of time and energy in chewing activities; (iii) decline in the rate of flow of digesta from the abomasum though not from the rumen; (iv) decline in digestibility in the whole tract of organic matter, nitrogen, and the structural carbohydrates; (v) decline in the digestion of fibre in the rumen relative to that occurring in the whole tract; (vi) decline in the quantities of volatile fatty acids and amino acids made available to the animal. By contrast only small differences attributable to maturity were observed in: (i) the distribution of digestion of organic matter between stomach and intestines; (ii) the digestibility of nitrogen other than ammonia in the intestines; (iii) the proportions of digestible organic matter derived from volatile fatty acids and amino acids; (iv) the proportions of individual amino acids in the digesta passing to the intestines. It was calculated that microbial protein contributed 33, 38, and 47% of the protein passing from the stomach to the intestines with the diets of advancing maturity. Most of the remaining protein was presumably of dietary origin. About 80% of the crude protein in the digesta was present in the form of amino acids, and the quantities of amino acids released in the intestines were calculated to be equivalent to 64-66 g/100 g crude protein intake. With advancing maturity of the diets the plasma levels of the essential amino acids except lysine, histidine, and arginine declined; there was little effect of diet on the plasma levels of non-essential amino acids. However, relative to total essential amino acids, the ratios of valine and leucine decreased with advancing maturity of the diet while those of lysine, histidine, glutamate, glycine, alanine, and serine increased. © 1969 CSIRO. All rights reserved.