The effect of supplementing grazing dairy cattle diets with fish oil and linseed oil on milk CLA and omega-3 fatty acid content.

摘要

In the recent years, there has been considerable interest in the potential health-promoting properties of both conjugated linoleic acid ( cis-9, trans-11 CLA), a fatty acid produced naturally in ruminant animals, and omega-3 fatty acids. The objectives of this research were to evaluate the effects of supplementing grazing dairy cows' diet with fish oil(FO)-linseed oil(LO) blend on milk cis-9, trans-11 CLA and omega-3 fatty acids milk content. In experiment one, fourteen lactating Holstein cows were randomly assigned to one of two treatment groups (7 cows/treatment) and fed either a control or oil supplemented diet for 21 d. Treatment groups were: (1) confinement cows with free access to corn silage and hay mix plus 10 kg/d (DM basis) grain mix supplementation (CONT), or (2) grazing cows with free access to grass pasture plus 10 kg/d grain mix supplementation containing 300 g FO plus 700 g LO (FOLO). Milk samples were collected during the last 3 d of the study and analyzed for chemical and fatty acid composition. Milk production (37.05 vs. 37.29 kg/d), milk protein percentages (3.16 vs. 3.21), and milk protein yield (1.05 vs. 1.25 kg/d) were not affected (P > 0.05) by treatment diets. Milk fat percentages (3.71 and 2.28) and yield (1.25 and 0.87 kg/d) were higher (P 0.05) with the CONT group. The concentrations of cis-9, trans-11 CLA (0.29 vs. 2.56 g/100g fatty acid) and vaccenic acid (VA; 0.81 vs. 7.14 g/100g fatty acid) in milk fat were higher (P 0.05) with the FOLO group. The concentrations of milk omega-3 C18:3n3, C20:5n3, and C22:6n3 were also higher (P 0.05) with the FOLO group. In experiment two, eighteen lactating Holstein cows who were randomly assigned to one of three treatment groups for 21 d. Treatment groups were (1) indoor cows with free access to corn silage and alfalfa hay plus 10 kg/d (DM basis) grain mix supplementation (CONT), (2) indoor cows with free access to corn silage and alfalfa hay plus 10 kg/d grain mix supplementation containing 300 g FO plus 700 g LO (FOLO), and (3) grazing cows with free access to grass pasture plus 10 kg/d grain mix supplementation containing 300 g FO plus 700 g LO (FOLOP). Milk samples were taken from each cow during the last 3 d of the study. Milk production, milk protein percentages and milk protein yield were not affected (P > 0.05) by treatment diets. Milk fat percentages (3.55, 2.85, and 2.39) and yield (1.20, 0.98, and 0.84 kg/d) were lower (P 0 .05) among the oil supplemented cows with cows on the FOLOP diet having the lowest values. Concentrations of milk cis-9 trans-11 CLA (0.33, 1.78, and 2.94 g/100g fatty acid) and VA (0.83, 5.09, and 7.15 g/100g fatty acid) were higher ( P 0 .05) among the oil supplemented cows and they were highest with cows on the FOLOP diet. Concentration of milk omega-3 fatty acids (0.5, 1.11, and 1.47 g/100g fatty acid) were higher (P 0.05) among oil supplemented cows and was also highest for cows on the FOLOP diet.;In conclusion cows fed diets containing the FO-LO blend resulted in higher milk concentrations of cis-9, trans-11 CLA and omega-3 fatty acids when compared to cows fed the CONT diet. However, greatest increases in cis-9, trans-11 CLA and omega-3 concentrations in the milk were achieved when the FO-LO blend was fed along with grazing.