Introduction feeding programs on the fatty acid composition of Material and methods

62 P . Bas, P. Morand-Fehr Livestock Production Science 64 2000 61 –79 Lorsque les rations sont riches en pulpes de betteraves ou en farine de poisson, la proportion de C est significativement 18:1 ´ ´ ¨ augmentee dans les tissus alors que les proportions de C , C et C sont abaissees. L’incorporation de maıs dans la 18:0 18:2 18:3 ˆ ´ ´ ration induit une augmentation de la teneur en acide linoleique dans les depots adipeux. L’incorporation de tourteau de coton ´ ´ ` induit un accroissement des teneurs en acides stearique et linoleique dans les tissus des agneaux. Les rations a base d’herbe ˆ ` ´ ´ ´ conduisent a des teneurs elevees en C et en C dans les depots adipeux des agneaux. Les variations du point de fusion 18:0 18:3 ´ ´ ´ ´ ` des tissus sous-cutane et perirenal sont fortement associees a celles des teneurs en C . Cette approche souligne les 18:0 ˆ ´ ´ ´ difficultes pour comprendre les effets d’un regime alimentaire sur la composition des depots gras et des muscles lorsque l’on ´ ne prend pas en compte tous les aspects de l’alimentation et de l’elevage. Bien que les lipides alimentaires soient fortement ´ ´ ´ ´ hydrogenes dans le rumen, cette etude montre l’amplitude des modifications des proportions des differents acides gras dans ´ les carcasses d’agneaux qui depend du choix des aliments de la ration.  2000 Elsevier Science B.V. All rights reserved. Keywords : Lamb; Fat deposits; Muscles; Fatty acid composition; Diet; Energy sources; Nitrogen sources

1. Introduction feeding programs on the fatty acid composition of

lamb adipose tissues and muscles from available Adipose deposits strongly influence the quality of bibliographic data. ruminant carcasses through their amount and com- position. The effects of nutritional factors on the proportion and body distribution of adipose deposits

2. Material and methods

´ have been reviewed by Vezinhet and Prud’hon 1975, Kempster 1981, Robelin 1986 and Bas Our work first consisted in selecting articles 1993. dealing with fatty acid composition of lamb adipose Nutritional factors have a lesser influence on the deposits and muscles, with a stress on those analys- fatty acid composition of adipose tissues and muscles ing the effects of dietary factors or having other in ruminants than in monogastrics because of the low objectives but supplying enough information on diets lipid content of their diet and of the hydrogenation of and feeding management. All the papers were taken dietary lipids in the rumen Wood and Enser, 1997; except when they did not provide sufficient infor- ¨ Nurnberg et al., 1998. Research on this topic has mation in one of the five following languages: been brought up to date again due to negative English, French, German, Italian or Spanish. consequences of ruminant fats in human dietetics. A data base was thus made up in such way that Studies on growing lambs have mostly focused on one observation corresponded to one group of lambs the effects of concentrate or fat levels and the type of in one experiment. All observations were character- cereals and fats added in diets. They have also aimed ised by explained variables fatty acids of adipose at analysing the effects of nutritional factors on meat tissues and muscles, characteristics of adipose de- organoleptic parameters, such as flavour and juici- posits such as melting point and softness index and ness, Melton, 1990, or the occurrence of defects in variables related with the animals, breed, live weight, firmness or colour of subcutaneous adipose tissues age, sex, etc., and with the diets or the feeding and meat Ørskov et al., 1974; L’Estrange and management, type and composition of diets, duration Mulvihill, 1975; Cazes et al., 1990. of milk feeding period or post-weaning period. The Some of these studies have shown that sheep variables of the data base, corresponding to the main present a specificity due to the influence of feeding animal characteristics, are reported in Table 1. on the fat composition of their carcasses, with a The fatty acid composition of seven tissues: particularly high proportion of odd-numbered and subcutaneous SC, perirenal PR, omental OM, branched-chain fatty acids Duncan et al., 1974; Bas mesenteric ME, intermuscular IN, intramuscular et al., 1980, 1998. MU, and whole carcass Car were analysed. The The aim of this work was to analyse the effects of locations of SC samples were, in decreasing order of the type of diet, energy and protein sources, and number of observations: the back 8th–12th rib, P . Bas, P. Morand-Fehr Livestock Production Science 64 2000 61 –79 63 Table 1 Main animal characteristics of the data base a b Sex n ADG Weaning age WA Slaughter LW SLW Slaughter age SA g day n weeks n kg n weeks n M 425 ,ADG,100 20 ,WA,5 190 SLW ,10 26 ,SA,5 38 F 136 10 ,ADG,150 69 5 ,WA,10 340 10 ,SLW,20 35 5 ,SA,10 73 C 174 150 ,ADG,200 73 10 ,WA,15 35 20 ,SLW,30 69 10 ,SA,15 141 Mixed sexes 152 200 ,ADG,250 122 15 ,WA,20 25 30 ,SLW,40 192 15 ,SA,20 188 250 ,ADG,300 157 20 ,WA,30 10 40 ,SLW,50 256 20 ,SA,50 161 ADG .300 74 SLW .50 81 SA .50 106 a Sex: M, entire males; F, females; C, castrated males; mixed sexes, entire males 1castrated males or entire males1females or castrated males 1females b ADG, average daily gain; LW, live weight; n, number of observations. dock tail basis, costal, leg, inguinal and sternal bibliographic data base thus formed contained 979 regions, the Semimembranosus and Triceps Brachii, observations from 108 papers. and around the fat tail. The information on the fatty Data were analysed by the Factor, GLM, REG and acid composition of MU came most frequently from Nlin procedures of SAS SAS, 1987. The GLM Longissimus dorsi, then from Semimembranosus procedure was used with the factors most frequently Table 3 and lastly from Triceps Brachii. represented. The variables concerning diet components were the type of forage and the main energy, protein, and fat sources in concentrates or in complete diets.

3. Results