Effects of fat source and copper on unsaturation of blood and milk triacylglycerol fatty acids in Holstein and Jersey cows

Fatty acid composition of plasma triacylglycerides and milk fat was analyze d from Holstein and jersey cows with control or depleted copper status and fed roasted whole soybeans or tallow. Conjugated linoleic acid in plasma wa s higher in Jersey cows. Dietary fat source influenced the proportions of a ll fatty acids in plasma and in milk, except for conjugated linoleic acid i n milk. Feeding soybeans increased plasma C-14:1, C-18:0, C-18:2, and conju gated linoleic acid, and decreased C-14:0, C-16:0, C-16:1, and cis- and tra ns-C-18:1 compared with feeding tallow. Low copper diets decreased C-18:0 a nd increased cis- and trans-C-18:1, and conjugated linoleic acid in plasma. A fat source x copper status interaction occurred for cis-C-18:1 in plasma . Proportions of C-4:0 to C-14:0 were higher, and cis(16:1), cis- and trans -C-18:1, and conjugated linoleic acid were lower in milk fat ofeTersey comp ared with Holstein cows. Generally, the effects of copper depletion were le ss apparent in milk than in plasma. Copper depletion increased C-4:0, trans -C-18:1, and conjugated linoleic acid, and decreased C-16:1 in milk. Feedin g whole soybeans increased C-4:0 to C-14:0, C-18:0, C-18:2, and C-18:3, and decreased C-14:1, C-16:0, C-16:1, and cis- and trans-C-18:1 in milk. Breed x fat interactions occurred for C-4:0, C-14:1, C-16:1, and conjugated lino leic acid in milk. Copper status x fat source interaction occurred for tran s-C-18:1. The breed x copper status interaction was apparent in milk fat fo r C-16:1 and C-18:0 and conjugated linoleic acid in milk. Both C-18:0 and t rans-C-18:1 were desaturated toy mammary tissue; however, whereas desaturat ion of C-18:0 was linear, desaturation of trans-C-18:1 reached a plateau th at could have been caused by presence of the trans-10 isomer, which is not desaturated and was not separated from trans-11 C-18:1 in our analysis. Com parison of the plasma triacylglycerol fatty acid profile with the milk fat profile was useful to interpret separate events of biohydrogenation in the rumen and desaturation by the mammary gland.