Thirty Assaf lambs, divided into three groups, equilibrated for live body weight (29.8 ± 1.88 kg), were used to study the effect of different dietary levels of protein on feed intake, animal performance and carcass characteristics. Three total mixed rations including barley straw, barley, corn, soybean meal, urea, molasses, soy oil, bicarbonate, vitamin-mineral premix, with a 15:85 forage:concentrate ratio, were formulated in order to supply 135 (LP group), 155 (MP group) and 175 (HP group) g of crude protein/kg dry matter. Animals were housed individually and had free access to fresh water. Feed was offered ad libitum and daily intake was recorded. Lambs were weighed once a week and they were slaughtered at the end of the experimental period (63 days). Carcasses were weighed before and after chilling for 24 hours at 4ºC and the following parameters were recorded or calculated: hot and cold carcass weight (HCW, CCW), chilling losses, carcass commercial yield and proportions of carcass joints. Data were subjected to analysis of variance, considering the protein content in the diet as fixed effect. Linear and quadratic trends were evaluated using orthogonal polynomial contrasts. Dry mater intake (DMI) was not affected (P>0.05) by dietary protein level, although DMI was numerically greater in HP than in LP group (1256, 1401 and 1464 g DM/day for LP, MP and HP groups, respectively). Average daily gain (221, 268 and 297 g/day for LP, MP and HP, respectively) and feed to gain conversion rate (5.82, 5.32 and 4.97 g DMI/g ADG for LP, MP and HP, respectively) increased (P0.05) by dietary treatment. Results suggest that increasing dietary protein content from 13.5 to 17.5% enhances performance throughout the fattening period.

Trabajo presentado al: 70th Annual Meeting of the European Federation of Animal Science. 26-30 August, Ghent, Belgium (2019).

Peer reviewed