Milk fatty acid profile and milk conjugated linoleic acid content of dairy cows fed diets with different carbohydrate sources with or without soybean oil supplementation

Milk fat from 12 7/8 crossbred Holstein-Zebu lactating dairy cows was used to evaluate the effect of different diets on milk fatty acid (FA) profile and milk CLA content. Cows were fed concentrate containing corn (CR). wheat bran (WB), or dried citrus pulp (CP) supplemented or not with soybean oil. Chromatographic analysis showed a FA recovery greater than 95%. With the exception of milk content of trans-10 C-18:1 and proportions of trans-10 C-18:1 and trans-11 C-18:1 on total milk trans-C-18:1, the interaction soybean oil x carbohydrate source was not significant for the remaining measured variables. Overall. carbohydrate source did not affect the milk FA profile or CLA content in this trial. Supplementation with soybean oil increased unsaturated FA by 35% and decreased saturated FA by 14%, mainly short chain FA (9.66 vs. 7.59 g/100 g) and medium chain FA (51.80 vs. 40.86 g/100 g). Soybean oil increased long chain FA (32.17 vs. 46.47 g/100 g). mainly C-18:1 (9.44 vs. 13.63 g/100 g), C-18:1 (20.28 vs. 29.74 g/100 g) and C-18:2 (2.16 vs. 2.92 g/100 g). Feeding soybean oil increased the concentration of cis-9 trans-11 C-18:2 CLA by 230% (0.46 vs. 1.06 g/100 g). In addition, the content of cis and trans-C(18:1)isomers was also increased. Although the trans-11 C-18:1 isomer was the most important, concentration of trans-10 C-18:1 increased from 0.28 to 1.11 g/100g in oil supplemented-diets being affected by the carbohydrate source. Milk from cows fed CR, WB, and CP showed similar content of trans-10 C-18:1. However, in diets with oil supplementation both CR and WB resulted in greater content of trans-10 C,8:, than CP diet suggesting different biohydrogenation pathways.