The effect of forage and breed of lambs on the fatty acid profile of intramuscular fat in m. longis-
simus lumborum (LL) and depot fat (SCF) above this muscle was investigated. The study was carried out in two replications on 36 Koluda sheep (KS) and Ile de France×KS (IF×KS) ram-lambs fattened intensively to 32–37 kg of body weight. Lambs were fed ad libitum the same concentrate mixture and different roughage supplements: grass hay in group C (control), field forage fed in a sheep house in group F, and pasture grazing (4 h/day) in group P. In the case of LL fat, the composition of fatty acids was found to deteriorate in lambs receiving forages compared to lambs from group C. Lambs grazed on pasture (P) had a higher content of LL fat (2.31 and 1.90% in P and C, respectively; P ≤ 0.05), a higher proportion of SFA (42.1 vs 39.6%; P ≤ 0.01), a similar proportion of MUFA, and a lower proportion of PUFA (10.4 vs 12.5%; P ≤ 0.05). With similar content of depot fat, changes in the FA composition of SCF fat were observed in F lambs compared to group C. Compared to C lambs, SCF of F and P lambs contained less SFA (5.16% vs 46.8; P ≤ 0.01 and 49.3%) and more MUFA (41.8% vs 45.6; P ≤ 0.01 and 43.6%), with a similar proportion of PUFA and higher CLA content in group P (by 17.8%). The crossing of KS with Ile de France meat rams did not result in any differences in LL fat content, with a generally unfavourable effect on FA composition and health quality parameters calculated on this basis. The present study showed an unfavourable effect of supplemental forage in intensive fattening of lambs on the fatty acid composition of intramuscular fat. However, both variants of forage use had a generally favourable effect on the lipid profile of subcutaneous fat.