A 4-year experiment has been conducted on finishing Belgian Blue cull cows of double-muscled type in order to study the effects of diets containing adequate levels of metabolizable protein, but either normal (NENP), low (LENP) or medium (MENP) levels of metabolizable energy, on animal performance, carcass and meat characteristics, and plasma metabolites and hormones. The LENP diet was offered during the whole (LENP group) or second half of the finishing (NENP-LENP groups), and the MENP diet during the whole finishing (MENP group). The degree of fatness required for the slaughter of animals from NENP groups was close to 4-5 (scale from 0 (very lean) to 5 (very fat)). In each underfed group, the slaughter of the animals was synchronized to that of NENP cows, by degressive degree of fatness. The same duration of finishing was thus obtained for all groups.
The experimental feeding strategies reduced the amounts of fat deposited in the carcass and the meat while muscle deposition was remarkably preserved. The proportions of saturated and monounsaturated fatty acids in intramuscular fat were also decreased while their proportions increased in plasma free fatty acids. Plasma insulin levels were also reduced and those ofIGF-1 were, surprisingly, maintained. The low energy diet promoted thus the settlement of a discrete lipolytic state while high levels ofIGF-1 preserved muscle deposition. This feeding strategy should be evaluated in other breeds of cattle.