Alpha-linolenic and linoleic acid in meat and adipose tissue of grazing lambs differ among alpine pasture types with contrasting plant species and phenolic compound composition

The special quality of foods from alpine grazing systems concerning their fatty acid (FA) composition is well established. However, the contribution of different specific vegetation types and the animal's genotype to this alpine effect is still unclear. In the present study, the FA profiles of muscle and adipose tissue lipids were determined in lambs that had grazed either an intensively managed lowland pasture or one of three characteristic alpine vegetation types differing in plant species number and composition, forage quality and amount, and composition of phenolic compounds and FA. On each vegetation type and in two subsequent years, two groups of lambs (seven Engadine sheep, ES; and seven Valaisian Black Nose sheep, VS) grazed for 9 weeks and were subsequently slaughtered (total n = 110 lambs). Forage samples, meat (Longissimus dorsi muscle, LD) and perirenal adipose tissue were analysed for their FA composition. Forages were additionally analysed for contents of phenolic compounds. Although proportions of alpha-linolenic acid (C18:3n-3) and linoleic acid (C18:2n-6) in plant biomass were clearly higher in the lowland compared to the alpine vegetation, the proportions of these FA were increased in the adipose tissue of alpine grazing sheep by 20-87% and by 26-58% in muscle compared to lowland grazing, depending on the alpine vegetation type. The levels of these two FA in body tissues differed between lambs having grazed different alpine pastures and were clearly positively associated with the contents of phenolic compounds in the vegetation but not with its lipid composition. Compared to the lowland pasture, conjugated linoleic acid (C18:2c9t11) in the tissues was lower when the lambs grazed alpine pastures, but did not differ between the alpine vegetation types. Slight breed differences were found, with a trend for higher proportions of long chain polyunsaturated FA at cost of saturated and monounsaturated FA in the VS compared to the ES. In conclusion, vegetation type is an important factor determining the FA composition in lamb meat and differentiating the alpine effect in this respect. The data clearly suggest that the plant secondary compounds in the swards prevented part of C18:3n-3 and C18:2n-6 from being hydrogenated in the rumen. Tissue-specific differences in incorporation of Cl 8:2n-6 and C18:3n-3 point to a physiological optimum level in the muscle but not in the adipose tissue. (C) 2013 Elsevier B.V. All rights reserved.