Fatty Acid Profile of Ruminal Fluid, Plasma and Milk Fat of Dairy Cows Fed Soybean and Sunflower Oil-Rich Diets, Without Effects on Milk Production

The objective of the study was to evaluate the effect of feeding soybean oil (SB) and sunflower oil (SF) on ruminal fluid, plasma and milk fatty acid profiles. Eighteen cows were obtained for the experiment and received 20 kg corn silage and 7.5 kg concentrate as a base diet, containing 6.2% palm oil on a dry matter basis, for four weeks. Subsequently, after the four-week experimental period, six cows were assigned to each of the dietary treatments. The treatments consisted of three groups: 1) the same base diet, containing 6.2% palm oil (control); 2) 6.2% SB; and 3) 6.2% SF. All treatments did not alter milk production. The milk fat percentages were significantly (P < 0.05) lower in the cows fed the SB- and SF-rich diets at day 7 and 14, whereas milk fat yields were significantly (P < 0.05) lower only in the cows fed the SF-rich diet at day 7. The proportion of ruminal C16:0 was significantly (P < 0.001) lower and C18:0 was significantly (P < 0.05) higher for the SB and SF diets, while in addition, C18:1n9 tended to be lower on the SF diet (P = 0.062). The proportions of plasma C16:0 and C18:1n-9 were significantly (P < 0.05) lower for the SB and SF diets, whereas C18:0 was significantly (P = 0.027) higher with the SB diet. Even though no differences in polyunsaturated fatty acids, in either the ruminal fluid or plasma, were found among the treatments, the proportion of milk linoleic acids (C18:2n-6) was similar in the SB and SF diets and both diets had proportions that were significantly (P < 0.001) higher than in the control. In addition, milk linolenic acids (C18:3n-3) were significantly (P < 0.05) greater in the SB diet than for the SF diet and for the control. An increase in the ruminal pH and a reduction in blood non-esterified fatty acid (NEFA) were detected in cows fed either the SB or SF diet. The results suggested (with the balance between dietary fatty acids hydrogenated in the rumen and taken up by the mammary gland) that SB is an acceptable fat source for high linoleic acid and linolenic acid (omega-6 and 3) and that SF is suitable for high linoleic acid (omega-6)-produced milk, without adverse effects on milk yield and composition. This practical feeding trial would reflect the use of these oils to produce