Influence of season and pasture feeding on the content of CLA isomers in milk from three different farming systems in Sicily.

It has been shown that several factors such as pasture feeding, farming system and season might influence the content of conjugated linoleic acid (CLA) isomers in milk. Four Sicilian traditional dairy farms were selected, two had both Holstein and Brown Swiss cows, which were both at low pasture intake regimen and the other two farms had exclusively Modicana local-breed cows fed at higher pasture intake regimen. Pasture was available during spring and autumn but not during summer. Additional hay and concentrate was supplemented during all periods. The objective of this study was to assess the season effect (spring, summer and autumn) and farming system effect on CLA isomers and total CLA contents in cows' milk. Autumn compared to summer milk had higher levels of total CLA (3,991.4 vs. 2,804.9 μg.g-1 of fat, respectively). Higher CLA levels in autumn compared to spring milk (3,991.4 vs. 2,662.7 μg.g-1 of fat, respectively) may be explained by different plant phenological stage. Spring compared to summer milk had surprisingly similar levels of total CLA (2,662.7 vs. 2,805.0 μg.g-1 of fat, respectively) this might be explained by higher diet content of concentrate in summer compared to the two grazing seasons (44.5 vs. 36.3% of DM). Milk total CLA levels did not differ significantly among farming systems. A significant variation of cis,trans (c,t) 11-13 and c,t 9-11 levels was only detected in milk from farms with higher pasture intake.