Effects of extruded linseed and level and type of starchy concentrate in a diet containing fish oil on dairy goat performance and milk fatty acid composition

Based on the potential benefits for long-term human health, nutritional strategies have been developed in order to increase the milk fat concentrations of bioactive fatty acids (FA) in ruminants. Dietary supplements of fish oil (FO), extruded linseed (EL) or a mixture of EL and FO increase c9,t11-CLA and n-3 PUFA in milk from bovine and caprine. These supplements associated with a high level of starch from concentrates cause milk fat depression in cows, but information for dairy goats is limited. An experiment was performed to investigate the effects of addition of extruded linseed to a diet containing fish oil in interaction with the type and level of starch concentrate on dairy goat performance and milk fatty acid (FA) profile. Following a 2 × 3 factorial design, 72 goats were allocated to 6 experimental diets based on alfalfa hay and with concentrates including fish oil (40 g/d) without or with extruded linseed (360 g/d) and either rich in starch from barley grain or extruded wheat or that were low in starch from barley grain. In contrast to cows, in goats adding extruded linseed to low-or high-starch diets based on hay and containing fish oil increases milk fat content and changes the milk FA composition in particular by increasing some bioactive FA with 18 carbons. In these conditions FA changes were characterized by decreases in SFA (on average 22% decrease) and increases in 18:0, c9-18:1, t11-18:1, c9,t11-CLA and 18:3n-3. The milk t10-18:1 concentration remained low (<1% total FA) and the t11-18:1/t10-18:1 ratio was much higher than in cows fed fish oil with plant oils. The combination of EL and FO induced larger concentrations in t11-18:1 and c9,t11-CLA than FO alone (2.9- and 2.1-fold higher, respectively). The apparent transfer rates of 20:5n-3 and 22:6n-3 from fish oil to milk were lower when EL was added to the diet (on average, 6.6 and 5.4%) compared to FO alone (on average, 8.0 and 7.4%, respectively). Extruded wheat, as the more rapidly degradable starch source in the rumen, decreased milk fat content. Based on the milk FA changes (e.g., c9,t11-CLA,18:2n-6, 18:3n-3, 20:5n-3, 22:6n-3), diets rich in starch from barley grain would induce a lower rumen bacterial biomass and a more extensive biohydrogenation of dietary FA in the rumen than diets rich in starch from extruded wheat. Starch level in the diets had negative effect on milk yield but moderate effects on milk fat and FA content, under these dietary conditions.