Soybean oil modulates the fatty acid synthesis in the mammary gland, improving nutritional quality of the goat milk

The objective of this study was to evaluate the productive performance, macro compounds and fatty acid (FA) profile of goats’ milk receiving diets supplemented with three amounts of soybean oil. Additionally, we tested to which extent lactating goats can positively respond to the influence of the soybean oil supplementation. Our hypothesis is that the FA profile in the milk will change with the increasing doses of soybean oil, i.e., the healthy FAs concentrations will increase and the concentration of harmful FAs will reduce. Eight primiparous Saanen goats weighing 39 ± 3.5 kg, with approximately 35 days of lactation and daily production of 1.8 ± 0.30 kg were evaluated. The experimental design was arranged as a double Latin Square 4 × 4. Goats were allocated in individual tie-stall pens and submitted to the following diets: control = 400 g/kg of dry matter (DM) of corn silage and 600 g/kg DM of concentrate without oil addition; 15 = 400 g/kg DM of corn silage and 585 g/kg DM of concentrate with addition of 15 g of soybean oil/kg of the diet’s DM; 30 = 400 g/kg DM of corn silage and 570 g/kg DM of concentrate with addition of 30 g of soybean oil/kg of the diet’s DM; 45 = 400 g/kg DM of corn silage and 555 g/kg DM of concentrate with addition of 45 g of soybean oil/kg of the diet’s DM. The soybean oil intake reduced daily milk production in all diets, except for diet 30. Production efficiency was not influenced by the diets. When compared to control, diet 45 resulted in an increase in the concentration of fat (29.1 %), lactose (4.9 %), total solids (10.4 %) and non-fat solids (5.7 %) in the milk, although it did not provide protein increase. Diet 45, when compared to the control, reduced the concentration of C8:0 and C10:0 FA by more than 60 %. Diet 45 also reduced by more than 26 % the total concentration of saturated FA (C12:0, C14:0, C15:0, C16:0 and C18:0), especially those with atherogenic properties such as C12:0 (97 %), C14:0 (40 %) and C16:0 (33 %). In addition, the inclusion of soybean oil increased the concentration of those FA that are beneficial to health, such as C18:1 cis-9, C18:2 cis-9, cis-12, C18:3 cis-9, cis-12, cis-15, C18:2 trans-10, cis-12 (antiobesity factor), C18:1 trans-11 (precursor for endogenous synthesis of rumenic acid), omega-3, unsaturated: saturated and PUFA: saturated ratios. The results corroborated our hypothesis that the healthy FAs concentrations increase and the concentration of harmful FAs will reduce with increasing oils doses in goats’ diet, in doses as high as 4.5 %. As far as we know, this is the first study that includes three concentrations of oil supplemented in the feed (accessing in more details the progressive changes in the FA milk profile) and that used a concentration as high as 4.5 % of oil.