Changes in goat milk fatty acids during abrupt transition from indoor to pasture diet

Abstract

Goal of this study was to evaluate the kinetics of goat milk fatty acids during abrupt transition from indoor to pasture-based diets. Twelve Valdostana goats in mid-lactation reared indoors and fed hay and concentrates for 40days were abruptly brought outdoors on natural pasture and fed fresh grass ad libitum. Feed samples and individual milk samples were collected for fatty acids analysis on the last day of indoor feeding (day 0) and after 1, 2, 3, 4, 6, 9, 13, 18 and 23days of fresh grass feeding. Milk fatty acid composition was significantly affected by sampling day. Significant changes already took place few days after transition. The most marked and consistent variations occurred at the expense of some unsaturated fatty acids. Total trans-octadecenoic and trans-octadecadienoic acids, conjugated linoleic acids (CLA) and omega-3 fatty acids constantly increased, reaching concentrations 4.0, 3.0, 3.9, and 2.2 times higher at the end of the trial than at its beginning, respectively. On the last sampling day the omega-6/omega-3 fatty acids ratio was two times lower than its initial value. Considering individual fatty acids, the most consistent and remarkable increasing trends throughout the trial were observed for C18:1 t6–11, C18:1 t12–14+c6–8, C18:1 c14+t16, C18:2 t11c15, C18:2 c9t13+t8c12, CLA isomers c9t11+t7c9+t8c10 and t11c13+c9c11. Alpha-linolenic and eicosapentaenoic acids also increased significantly, but to a lesser extent. In view of the many beneficial biological effects that have been attributed to vaccenic acid (C18:1 t11), rumenic acid (C18:2 c9t11), and omega-3 fatty acids, results showed that, from a human health perspective, goat milk fatty acid composition consistently improved after transition from indoor to pasture feeding. Such improvements, mainly due to the high content of α-linolenic acid in pasture plants, were already significant after two or three days of fresh grass feeding. Further increases of beneficial fatty acids in milk fat were observed till about thirteen (vaccenic acid and CLA) or twenty-three (omega-3 fatty acids) days after transition. These results show that pasture can be considered a natural feeding strategy to quickly enhance the healthfulness of goat milk fat.