Blood metabolites and fatty acid composition of milk and cheese from ewes fed oilseeds

Sixteen lactating Dorset ewes were used in a completely randomized design to determine the effects of oilseed supplementation on milk yield and composition, blood metabolites, cheese yield and composition and fatty acid profile of milk and cheese. Four iso-nitrogenotis diets were formulated: a control diet (CT) with no oilseed supplementation, a flaxseed supplemented diet (FS), a sunflower seed supplemented diet (SF), and a canola seed supplemented diet (CS). Oilseed-supplemented diets were formulated to contain 7% fatty acids. Feeding oilseeds had no effect on dry matter intake. Milk yield was similar for ewes fed CT, FS and SF and was higher (P < 0.05) than that of ewes fed CS. Ewes fed oilseed-supplemented diets produced milk with higher (P < 0.05) protein and total solid percentages than those fed CT. However, milk fat percentage was only higher (P < 0.05) in the milk of ewes fed FS and SF relative to those fed CT. Actual cheese yield was higher (P < 0.05) from milk of ewes fed oilseed-supplemented diets relative to those fed CT. However, cheese composition was not affected by dietary treatments. Plasma concentrations of fatty acids and cholesterol were increased (P < 0.05) while plasma concentration of beta-hydroxybutyrate (PHBA) was decreased (P < 0.05) by oilseed supplementation. However, plasma concentrations of glucose and mammary extraction rate of plasma metabolites were not influenced by oilseed feeding. Oilseed supplementation increased (P < 0.05) concentrations of unsaturated fatty acids in milk fat. The order of increase was SF > FS > CS. Feeding SF, FS and CS increased (P < 0.05) conjugated linoleic acid (CLA) concentration in milk by 83.5, 39.2 and 16.5%, respectively. Concentration of linolenic acid in milk was only increased (P < 0.05) by feeding FS. Changes in milk fatty acid profiles were reflected in the cheese.