Utilization by fattening sheep of the energy and nitrogen in fresh herbage and in hay made from it

Abstract

Balances of energy, carbon, and nitrogen were measured with fresh herbage cut at 28 days' regrowth, and with hay made from it. Measurements were made on four wether sheep at fasting and at four levels of feeding. The herbage contained paspalum grass and white clover in proportions ranging from 0.6 : 1 to 1.2 : 1, with dry matter between 11 and 17%. It contained (dry matter basis) : 10% ash, 3% soluble sugars, 25% cellulose, 23% crude protein, and 9% lignin; crude fibre was 22% and nitrogen-free extractives 42%. The hay had the same composition. Digestibility of organic matter was 75% for the fresh material and 73% for the hay; digestible energy values were 73 and 70% respectively. The difference between fresh herbage and hay was due entirely to a decrease in the digestibility of protein, from 82% to 73%, in drying. Efficiency of utilization of digested protein was not affected. Digestibility of both materials decreased by 2 to 4 units between the lowest and highest feeding levels. One other difference was found, viz. the ratio methane production/kcal digestible energy was 1–2% greater with the hay. Metabolizable energy was 82–84% of digestible energy for both materials. Heat production bore a linear relation to metabolizable energy above maintenance. Net availability of metabolizable energy was 75% between fasting and maintenance, and 52% above maintenance, for both the fresh and dry food. These quantities were predictable to within 8% from metabolizable energy or fibre digestibility; the normally used starch equivalent factors underestimated the correct values by some 25%.