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

Summary

The special quality of foods from alpine grazing systems concerning their fatty acid (FA)composition is well established. However, the contribution of different specific vegetationtypes 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 hadgrazed either an intensively managed lowland pasture or one of three characteristic alpinevegetation types differing in plant species number and composition, forage quality andamount, and composition of phenolic compounds and FA. On each vegetation type and intwo subsequent years, two groups of lambs (seven Engadine sheep, ES; and seven ValaisianBlack Nose sheep, VS) grazed for 9 weeks and were subsequently slaughtered (total n = 110lambs). Forage samples, meat (Longissimus dorsi muscle, LD) and perirenal adipose tissuewere analysed for their FA composition. Forages were additionally analysed for contentsof phenolic compounds. Although proportions of a-linolenic acid (C18:3n-3) and linoleicacid (C18:2n-6) in plant biomass were clearly higher in the lowland compared to the alpinevegetation, the proportions of these FA were increased in the adipose tissue of alpine graz-ing sheep by 20–87% and by 26–58% in muscle compared to lowland grazing, dependingon the alpine vegetation type. The levels of these two FA in body tissues differed betweenlambs having grazed different alpine pastures and were clearly positively associated withthe 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 waslower when the lambs grazed alpine pastures, but did not differ between the alpine vegeta-tion types. Slight breed differences were found, with a trend for higher proportions of longchain polyunsaturated FA at cost of saturated and monounsaturated FA in the VS comparedto the ES. In conclusion, vegetation type is an important factor determining the FA com-position in lamb meat and differentiating the alpine effect in this respect. The data clearlysuggest that the plant secondary compounds in the swards prevented part of C18:3n-3 andC18:2n-6 from being hydrogenated in the rumen. Tissue-specific differences in incorporation of C18:2n-6 and C18:3n-3 point to a physiological optimum level in the muscle but notin the adipose tissue.