Características de carcaça e componentes não-carcaça de cordeiros em função do consumo alimentar residual

Abstract

The objective was to evaluate lamb RFI and study its relationship with carcass and non-carcass components. Three month old Dorper crossbred lambs (47), were allocated to two experimental periods of 56 days each, after a 15-d pre experimental period. During the first period, 20 lambs (from 25.89±1.72 to 43.68±2.55 kg of body weight) and in the second period, 27 lambs (from 27.28±1.87 to 42.51±3.59 kg of body weight) were used. Every fifteen days weights were taken and backfat thickness (BT) measured on the Longissimus dorsi muscle between the 12ndand the 13th ribs. After slaughter internal organs were weighed, the carcass was split in half and the left-side cuts (hind-legs, shoulder, loin, ribs, rack and neck) weighed and their proportions in relation to the cold carcass weight calculated. Legs were dissected for the determination of muscle, bone and fat proportions. Residual feed intake adjusted for live animal measures of body composition (averages daily gain and metabolic mid-point weight; RFI1) ranged from -0.148 kg d-1to 0.230 kg d-1 (SD= 0.080 kg d-1). A second RFI (additionally adjusted for gain in ultrasound backfat thickness; RFI2) ranged from -0.130 kg d-1 to 0.189 kg d-1 (SD= 0.073 kg d-1).The effects of RFI1 and 2 efficiency classes (positive or less efficient, intermediate, negative or more efficient) on carcass and non-carcass component weights and yields were analyzed by the GLM procedure of SAS® and means compared by the Tukey-Krumer test at 5% significance. Warm carcass, shoulder, loin and total fat weights were greater (P<0.05) for RFI1-negative compared to RFI1-intermediate animals (22.4±0.4 and 21.5±0.4g, 2.02±0.04 and 1.87±0.04g, 0.48±0.19 and 0.41±0.02g, 0.41±0.02 and 0.34±0.02g, respectively).Loin weight and percentage yield were greater (P<0.05) for RFI2-negative compared to RFI2-intermediate animals (0.49±0.02g and 0.40±0.02g, 2.27±0.09 and 1.95±0.07%). Muscle yield was different only in RFI2-classes, such that, it was greater (P=0.02) in intermediate (66.05±0.7%) then in positive animals (62.54±0.9%). Non-carcass components were not different between classes in both RFI equations. Although RFI-negative animals had lower feed intakes, their carcass values were adequate, especially for prime cuts, and this finding underscores the importance of genetic selection based on residual feed intake.