Tanker milk variability in fatty acids according to farm feeding and husbandry practices in a French semi-mountain area

The objective of this study was to relate farm feeding practices in different production systems to milk fatty acid (FA) composition on the scale of round tankers. Milks from 10 collection rounds in the French department of the Haute-Loire (10 to 36 herds per collection round) were sampled twice and three times during winter and grazing periods, respectively. The collection rounds were principally characterised by the forage system (grass or maize silage). Nine variants of milk production conditions were defined: four for the winter feeding period (W1 to W4) and five for the grazing period (G1 to G5). Over the year rumenic acid was positively correlated with vaccenic acid (r = 0.99), all the other trans and c11 isomers of C18:l, oleic acid (r = 0.79), linolenic acid (r = 0.82) and eicosapentaenoic acid (C20:5n-3, EPA). The milk fat from cows grazed on grass had a higher proportion of total trans FA (including trans C18:l, non-conjugated C18:2 and c9t11-CLA) and total cis C18:1, and a lower proportion of medium-chain saturated FA (−9.50 g·100 g−1 for C16:0 between G5 vs. W1) and monounsaturated FA (mainly c9-C16:l) than that from grass silage-based (and concentrate-supplemented) diets. Also, anteiso-15, C18:0, c9-, t6+7+8-, t9-, t11- and t13+14-C18:1, c9t11-CLA (r = 0.65), t11c15-C18:2, C18:3n-3 (r = 0.68) and EPA (r = 0.64) were positively linked to permanent grassland forages (green or conserved) on the scale of the year. During winter, trans (t6+7+8, t10, t12 and t13+14) and cis (c12, c13 and t16+c14) isomers of C18:1 were positively correlated with the proportion of maize silage in the diet (r = 0.47 to 0.91). The wide range of milk FA composition from the rounds observed in this study was closely linked to the variants in feeding and husbandry conditions. Our data confirm the strong effect of nutritional factors on milk FA composition of tanker milk shown in experimental trials.