Factors affecting the nutritive value of grass silages, with special reference to protein nitrogen

Factors affecting the nutritive value of silage were highlighted, in the Literature Review, along with silage biochemistry, additives, protein metabolism in the ruminant and the nylon bag technique. The nutritive value of two silages (made from second-cut Perennial and Italian ryegrass), one pretreated with 6.0 It⁻¹ formic acid before ensiling (s) and the other with 7-5 It⁻¹ formalin (F), was assessed. In Experiment 1, the two grass silages and a control complete ruminant diet (C.R.D.) were offered ad libitum to 2I4 Crossbred lambs. C.R.D. had a significantly greater (p< 0.001) daily DMI than the two silages between which there was no significant difference in intake. The high intake of C.R.D. was attributed to its high concentrate content and its pelleted form and explained the significantly higher (P< 0.001) liveweight gains than from the silage diets. The silages did not differ significantly in liveweight gain. Silage F and C.R.D. had higher efficiency of feed conversion (P< 0.0^) than Silage S. In Experiment 2, 12 Crossbred lambs were randomly allocated to the three diets and fed in metabolism cages. Silage S had similar apparent digestibility coefficients to an untreated control, but Silage F had lower apparent digestibility coefficients for 0M, DM energy and crude protein. The latter was significantly lower than those of the two other diets. C.R.D. had significantly higher CP digestibility than Silage F and significantly greater N retention than F and S, but was lower in all other parameters, due to its high straw content. Silage F displayed better efficiency of nutrient utilization than Silage S. In Experiment 3, the two silages and an untreated control silage were incubated in artificial fibre bags in the rumen for 1, 4, 12, 24.