Influence de la vitesse de croissance sur la composition du gain de poids des bovins : variations selon la race et le sexe

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Abstract
Variation in the composition of body weight gain with growth rate was measured by the slaughter technique in Friesian and Charolais .times. Salers male cattle and Charolais .times. Salers heifers fattened between 280-300 kg and 480-540 kg body wt. For the same growth rate (1 kg/day), the heifers retained more lipid and energy and less protein than the Charolais .times. Salers bulls (310 vs. 160 g, 3830 vs. 2700 kcal and 161 vs. 205 g, respectively). The Friesian bulls were located between Charolais .times. Salers bulls and heifers. When the growth rate increased with increasing energy intake, the weight of lipids, proteins and the energy retained increased with daily gain raised to the power 1.78, 0.73-0.83 and 2.43, respectively. The lipid content and the caloric value (kcal/kg) of the gain increased while the protein content decreased. These results are compared to previous data about the effect of the feeding level on the body composition of cattle. The consequences of this variation in the composition of the gain on the requirements of animals for growth are discussed.