Milk fat composition of Holstein and Jersey cows with control or depleted copper status and fed whole soybeans or tallow

We studied effects of breed, dietary fat source, and dietary copper intake as factors known to influence unsaturation of milk fat and its potential fo r development of spontaneous oxidized flavor in milk. Twelve Holstein and 1 2 Jersey cows were allotted to three blocks with four cows of each breed. C ows within breed were allotted randomly within blocks and fed control or co pper-depleting diets for 2 mo to achieve stable or depleted liver copper st ores. Cows then were fed tallow or roasted whole soybeans in a two-period s witchback (5 wk per period); during the last week of each period additional vitamin E (2000 IU/d) was added. Copper depletion for 2 mo decreased conce ntrations of copper in liver. Feed intake and milk yield were influenced on ly by breed. The proportions of C-4:0 to C-14:0 and C-18:0 in milk fat were higher, whereas C-16:1 and cis-C-18:1 were lower in Jersey cows. Feeding s oybeans increased C-4:0 to C-14:0, C-18:0, C-18:2, and C-18:3 in milk, and decreased C-14:1, C-16:0, C-16:1, trans-C-18:1, and cis-C-18:1. Depleted co pper status increased conjugated linoleic acid in milk. Several breed x fat source interactions for individual milk fatty acids occurred. Feeding soyb eans decreased plasma concentrations of copper and zinc, and increased conc entrations of alpha-tocopherol in plasma and milk. The concentration of zin c was higher in milk of Jersey cows. Depleted copper status tended to incre ase copper concentration in plasma and decreased copper in milk. Fat source did not influence plasma copper concentration when status was adequate, bu t plasma copper concentration was higher when tallow was fed to cows with d epleted copper status. Supplementing vitamin E increased concentration of a lpha-tocopherol in plasma and milk and decreased concentration of zinc in m ilk. Factors influencing the potential for oxidized flavor development in m ilk can be manipulated by changing the diet of the cow.