Abstract
The objective of this trial was to study the effects of diets with low (L, 45% diet DM) or high (H, 65% diet DM) percentage of concentrate combined with the addition of extruded soybeans (SB) or rolled canola seeds (CS) on the performance of dairy goats and milk fatty acid (FA) composition. Twenty-four Saanen or Alpine goats were used in an 8 wk trial with the first 2 wk for the adaptation to one of the 4 experimental diets (L-SB, L-CS, H-SB, H-CS) accordingly to a 2×2 factorial arrangement. Individual milk production and gross composition were recorded weekly and milk FA was analyzed in the middle and at the end of the trial. The dry matter intake was similar among groups, but total FA intake was higher in H-CS group. The dietary treatments did not affect the milk yield (kg/d), the contents (g/kg) and yields (g/d) of fat and protein, the yield of lactose and the content of urea; however feeding H-CS diet increased the content of lactose. The dietary treatments did not affect the proportion of FA from C4:0 to C10:0 in milk fat. Feeding H rations increased the percentage of trans-C18:1 (t6+7+8 and t9 to t12-C18:1), c9,c12-C18:2 and c9,t11-C18:2 at the expense of C14:0, c9,c12,c15-C18:3 and the iso and ante-iso FA. Feeding CS increased the C18:0 and total trans-C18:1 whereas SB raised the C16:0 and c9,c12-C18:2. The milk from H-CS group was the richest in trans FA, but the extent of the response of the trans FA was slightly different according to the isomer: it was higher for t6+7+8-C18:1 than for t11-C18:1. Feeding high concentrate diets combined with dietary fat can be used to modify the FA profile of goat milk, without any negative effect on milk yield and milk fat or protein contents. Their effects may be complementary, at least for trans-FA. Moreover, the profile of trans isomers relative to total trans-C18:1 seems dependent on the source of dietary fat.
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