Reduction of cereals in ruminant diets contributes to reducing the feed-food competition, and new strategies are required to reduce the use of maize silage while preserving profitability of beef fattening production systems. Haylage from permanent pasture is an interesting alternative to maize silage as the main forage in the diet although possibly leading to lower fat deposition and higher methane emissions than maize silage because of differences in the profile of absorbed nutrients. The present paper presents data from an experiment with young growing Charolais bulls fed two iso-net energy and iso-CP rations based on haylage or maize silage and differing in their proportions of starch and fibre, offered at two levels of net energy intake. Two trials were conducted. In a feeding trial, 36 weaned bulls were individually fed over the whole fattening period, and slaughtered at the same final BW of 700 kg at 15–18 months of age. Intake, weight gain, adiposity (body condition score and adipocyte size), 6th rib composition and behaviour (eating, drinking, social encounters, standing still, moving, lying) of the animals were measured. The tissue and chemical composition of the whole body and carcass at slaughter were calculated from the rib composition. A balance trial, conducted in parallel, used eight bulls to measure diet digestibility, nitrogen balance, and the production of enteric methane. The data obtained in the two trials describe the impact of the nature of the dietary net energy on performance and fat deposition and separate it from the influence of net energy intake level hence of growth rate; it is of interest to develop nutritional strategies for beef cattle. Scientifically data are of interest to test the limits of existing feeding systems or growth models and predict dynamic changes in body and carcass composition with time. From an applied point of view, data show a lower efficiency of use of the haylage ration.
Sepchat et al. (Thu,) studied this question.