EFFECT OF FAT SUPPLY TO FATTENING DIET ON GROWTH AND CARCASS QUALITIES OF EARLY WEANED MALE LAMBS FED INDOORS DURING WINTER [French]

摘要

The effect of dietary fat supplies was investigated for growth and carcass characteristics on 270 Lacaune male-lambs randomized and fattened in 3 pens indoors during winter. Two treatments were compared with classical starter and fattening diets: i) 21 kg commercial starter then a commercial 'growing-fattening' diet; ii) 21 kg starter supplemented with coconut oil then the 'growing-fattening' diet supplemented with lard; iii) 17 kg starter supplemented with coconut oil then the reference commercial 'growing-fattening' diet. The 2 starling diets were isocaloric and isonitrogenous (ME = 10.9 MJ/kg DM; CP = 189 g/kg DM). One was supplemented with 5% coconut oil (fat (F) = 74 g/kg DM) and fed at 2 levels (21 kg/lamb during 29 d vs 17 kg/lamb for 21 d). The second was a reference commercial starter diet (F = 31.6 g/kg DM) issued at 21 kq/lamb level. The 2 succeeding growing-finishing diets were also both isocaloric and isonitrogenous (ME = 10.7 MJ/kg DM; CP = 176 g/kg DM). One was supplemented with 3% lard (F = 50.4 g/kg DM) and the other was a reference commercial diet (F = 37.5 g/kg DM). All diets were given ad libitum and straw was freely accessible. The lambs were weaned early (3-5 weeks old) and were slaughtered at a fixed body weight (BW = 39 kg) in one slaughterhouse. Carcasses were scored by the same skilled operator. From these, and for statistical purposes owing the discrepancy in the frequency distribution of initial parameters of lambs, 2 sub-samples were made and standardized according to a normal distribution and in respect to the weight at weaning (12 kg; 3 x [n = 58]), the relative growth between 0-20 d (16.2 g/d/g BW; 3 x [n = 64]). Concerning growth, feeding with starter diet over an extended time produced a higher growth rate on final fattening stage (+5%, P < 0.04). Coconut oil did not promote growth during the starting stage. However, through a remaining effect, it improved the conversion food ratio in the last fattening stage when lard diet was associated (CFR = 3.6 for treatment a vs 3.0 kg DM/kg gain; P < 0.05). Supplementing with lard in the 'growing-finishing' diet did not modify the lamb growth. in the 3 lots, the conversion food ratio increased until the lambs reached about 32% of their mature weight. The relative growth came close to a maximum when lambs weighed about 22% of BW at maturity (17.5 g/kg BW), then it regularly decreased to 10 g/kg BW at the end. Concerning the characteristics of carcasses, only coconut oil supplementation during the starting stage induced a greater proportion of carcasses with very firm subcutaneous fat (27 vs 13%, P < 0.03) and reduced the proportion of soft and oily class of disqualitative carcasses (17 vs 33% P < 0.02). However the colours of the layer ro, fat were not affected.