Feeding dairy cows with full fat extruded or toasted soybeans seeds as repalcement of soybean meal and effects on milk yield, fatty acid profile and CLA content

The aim of this study was to evaluate the effects of the replacement of about 70% of soybean meal (SBM) with extruded (ES) or toasted (TS) full-fat soybean seeds in diets for lactating cows on milk quality, fatty acid profile, and conjugated linoleic acid (CLA) content. Eighteen lactating cows were assigned to 3 groups which received a basal diet, supplemented with 1.8, 2.1 and 2.1 kg/head, respectively, of SBM, ES and TS. There was no significant effect on milk yield, calculated as the difference between daily yield during the experimental period and the mean of the last 5 days of adaptation (-1.65, -1.29 and -0.20 kg/d, respectively, for SBM, ES and TS; P>0.10) and milk quality parameters (fat, protein, urea and cheese making parameters) among treatments. In the ES group there was a decrease in the short chain FA content (from C4 to C13) in milk fat (9.2 vs 11.0 and 10.8 g/100 g lipids, respectively, for ES, SBM and TS; P<0.05). Medium chain FA (from C14 to C17) content in milk fat was lower for ES and TS groups compared with SBM (46.8 and 48.0 vs 54.8 g/100 g lipids respectively; P<0.01), while long chain FA (C≥18) concentration in milk fat was lower in the SBM group compared to the others (34.3 vs 44.2 and 41.2 g/100 g lipids, respectively, for SBM, ES and TS; P<0.001). The replacement of SBM with ES enhanced oleic and linoleic acid and, particularly, CLA content. Intermediate values were observed for the TS group. CLA content (0.91, 0.62 and 0.56 g/100 g lipids, respectively, for ES, TS and SBM; P<0.05) increased throughout the trial in all groups. ES also reduced the proportion of SFA with respect to SBM (65.2, 68.2 and 70.9 g/100 g lipids, respectively, for ES, TS and SBM; P<0.05), and increased MUFA (26.9, 24.5 and 23.1 g/100 g lipids in the same order; P<0.05) and PUFA (7.4, 6.9 and 5.5 g/100 g lipids in the same order; P<0.05) of milk fat, thus improving the health-quality of milk. The various soybean products did not affect either metabolic profile (protein, urea, glucose, cholesterol, NEFA, triglycerides, liver parameters and mineral serum content) or rumen parameters (pH, ammonia and VFAs). The replacement of SBM with ES and TS permitted an improvement in the nutritional properties of milk without negatively affecting animal performances.