The digestion of barrel medic (Medicago truncatula) hay and seed pods by sheep

Abstract

Experiments were conducted to determine the digestion and utilization of barrel medic hay and pod fed separately to penned sheep. Estimates were made of intake and digestion in the whole tract. Rates of passage of digesta from the stomach and intestines were estimated by reference to radioactive markers. The organic matter of pod contained 23.8% crude protein, 5.2% long-chain fatty acids and 77.5% acid-detergent fibre including 19.9% lignin. Organic matter digestibility was only 24.3%, largely because of poor digestibility of fibre. Protein utilization was inefficient because of high loss of dietary protein in the rumen and poor digestibility in the small intestine. Only 20.3% of protein intake was absorbed from the small intestine. High loss of protein in the rumen was verified by high rumen ammonia levels, 52 mg nitrogen/100 ml rumen liquor. Long-chain fatty acids present in the pod diet, mainly in polyunsaturated form, were extensively hydrogenated in the stomach. Although only a small loss of fatty acids occurred in the stomach, 72% of the intake was absorbed from the small intestine. Pods provided only small amounts of nutrients, derived mainly from the digestion of seeds. However, energy derived from pods should be used efficiently, as a high proportion of absorbed nutrients consisted of long-chain fatty acids and amino acids. Barrel medic hay had an organic matter digestibility of 65% and contained 16.9% crude protein. Digestibility of organic matter in the stomach and intestines resembled that of lucerne, and it was concluded that barrel medic hay was similar in nutritive value to good quality lucerne hay.