Occurrence of conjugated cis-9,trans-11-octadecadienoic acid in bovine milk: effects of feed and dietary regimen.

Twenty-eight lactating cows were used to study the effects of different diets and different dietary regimens on the variation of cis-9,trans-11-octadecadienoic acid in milk. Cows were divided into three groups and assigned to dietary treatments differing in the ratio of forage to concentrate. The control group was fed a diet with an average ratio of forage to concentrate of 50:50. The two trial groups were fed a trial diet either in restricted or nonrestricted amounts. Variation of cis-9,trans-11-octadecadienoic acid in milk was substantial (2.5 to 17.7 mg/g of fat). Cows fed restricted amounts of the trial diet, which contained a lower forage to concentrate ratio than did the control diet, exhibited, on average, the highest concentration (11.28 mg/g of fat). For cows fed for ad libitum consumption, the trial diet did not differ significantly from the control diet (6.6 vs. 5.0 mg/g of fat). The concentration of cis-9,trans-11-octadecadienoic acid and trans-11-C18:1 was positively correlated. Therefore, conjugated linoleic acid in bovine milk, if considered to be beneficial, could be increased through a suitable dietary regimen.