Supplementation of silage diets with fish meal (a low rumen degradable protein) has resulted in increased live-weight gains in steers (England & Gill, 1985). This response has been attributed to increased dietary protein escaping degradation in the rumen and being digested in the small intestine. Fish meal however is expensive in monetary terms. More recent work (Jacobs and McAllan, 1992) showed that rapeseed meal (a highly rumen degradable protein) supplementation of silage diets given to growing steers resulted in significant increases in live-weight gains similar to those obtained with fish meal supplements. The response to rapeseed meal was probably a result of enhanced microbial protein synthesis in the rumen as a result of synchrony of available energy and nitrogen nutrients, thus increasing microbial (and hence) total protein flow to the small intestines, producing a similar overall response to fish meal. The object of this experiment was to further evaluate the use of rapeseed meal as an alternative to fish meal

Two silages, 60D (low digestibility, L) and 70D (high digestibility, H) were prepared from minimum wilt first cut perennial ryegrass (mixed sward). The grass was cut with a disc mower and picked up with a precision chop harvester.