Effect of soybean oil supplementation on milk fatty acid composition from Saanen goats fed diets with different forage:concentrate ratios

Twelve lactating Saanen goats were randomly assigned to four experimental diets, which differed in terms of forage: concentrate ratio and soybean oil supplementation. A 4x4 Latin square design was used. On a dry matter (DM) basis, forage: concentrate ratios were 63:37 ('high-forage' diet) and 35:65 ('low-forage' diet/high beet pulp). These diets were given either with oil (100 g.d(-1)) or without. The inclusion of soybean oil in the diet resulted in a significant increase in milk yield (but with HF diet) and in milk fat yield and concentration (P<0.05). Milk protein content remained unchanged across the diets. Milk protein yield was, however, higher for the high-forage diet containing added oil (forage x oil interaction, P<0.05). Soybean oil in the diet modified the milk fatty acid composition, reducing the levels of medium-chain and saturated fatty acids and increasing the levels of C18:2 n-6 and conjugated linoleic acid (CLA). The addition of soybean oil to the diet resulted in a significant increase in rumenic acid (cis-9, trans-11 CLA) and vaccenic acid (trans-11 C18:1) content in the milk fat. Interactions between forage and oil resulted in a significant increase in rumenic acid and vaccenic acid in animals fed a high-forage plus oil diet, and in trans-10 C18:1 and trans-10, cis-12 CLA in animals fed a low-forage plus oil diet, probably due to a shift in the rumen's biohydrogenation of linoleic acid.