Effect of dietary starch concentration and fish oil supplementation on fatty acid profile and microbial composition of rumen fluid in lactating dairy cows.

AbstractThe aim of this study was to evaluate the effects of diets with different starch concentration and fish oil (FO) supplementation on fatty acid (FA) profile and changes in microbial population of rumen liquor in lactating dairy cows. The experiment was conducted as 4 X 4 Latin square design with a 2 x 2 factorial arrangement: i) 2 concentration of dietary starch (low vs. high: 23.7 and 27.7% on DM) basis; ii) the presence or absence of FO (0.80% on a DM basis); and their interaction has been evaluated. Four Italian Friesian cows, in 4 consecutive 26-d period, were fed the following diets: i) low starch (LS); ii) low starch plus FO (LSFO); iii) high starch (HS); iv) high starch plus FO (HSFO). At the end of each experimental period the rumen liquor was sampled and analyzed for FA profile and microbial composition. The percentages of C16:1 cis9 (P=0,0483), C18:1 trans6-8 (P=0,0060), C18:1 trans11 (P=0,0219) and C22:6 n-3 (P=0,0183) were significantly increased in the rumen liquor by the FO supplementation while the total saturated FA percentage decreased. Butyrivibrio fibrisolvens, Prevotella spp. (involved in the biohydrogenation pathway (BH) of polyunsaturated FA), Ruminococcus albus, Ruminobacter flavefaciens and total protozoa content were not affected neither by starch level neither by FO inclusion in the diets. In contrast Streptococcus bovis, a pectin fermenting species, increased with LS diets (P=0,0491), according to a higher content of neutral detergent fiber and a lower starch content of the diets. At the dosage tested, FO did not induce perturbation in the rumen microbial community, but improved the concentration of several functional FA (C18:1 trans11 and C22:6 n-3) without promoting the shift of the BH toward the C18:1 trans10 production, as previously reported.