THE EFFECT OF LIPID SUPPLEMENTS ON THE POPULATION OF SELECTED RUMINAL BACTERIA VARIES WITH THE FATTY ACID COMPOSITION

There is an increasing body of evidence that conjugated linoleic acid (c9t11 CLA) suppresses chemically induced tumor development in cell cultures and animal models. Ruminant-derived foods make a major contribution to total fat consumption and are the main source of c9t11 CLA in the human diet. In light of the potential benefits to long-term human health, there has been increased interest in enhancing the concentrations of potentially beneficial fatty acids (FA) in milk and meat. Factors affecting c9t11CLA production and secretion into milk fat have been extensively studied the last 10 years and a large pool of knowledge has accumulated. However, little information is currently available about the effects of feeding c9t11 CLA- stimulating diets on rumen microbial ecology, particularly, bacterial species believed to be involved in the biohydrogenation (BH) process. The main objective of this study was to evaluate the effect of lipid source on the DNA concentrations of selected ruminal bacteria. Four continuous culture fermenters were used in 4 x 4 Latin square design with four periods of 10 d each. Treatment diets were fed (45 g/d DM basis) in three equal portions during the day. The diets were 1) control diet (50% alfalfa pellets, 50% concentrate, CON), 2) CON plus saturated fat (rumofat; SAT), 3) CON plus soybean oil (SBO), and 4) CON plus fish oil (FO). Lipid supplements were added at 3% of diet DM. Lipid supplements had no effect on feed digestibility, total VFA and acetate concentrations or fermenter pH. Propionate concentration was higher with the FO diet in comparison with the other treatment diets. Butyrate concentration was similar between the SBO and FO diets and both were lower than the levels for the CON and SAT diets. The concentration of VA in effluents increased with SBO and FO diets and was highest with SBO diet. The concentrations of C18:0 in effluents were lowest for the FO diet compared with the other treatment diets. The concentrations of c9t11 CLA in effluents were similar between SBO and FO diets and both were higher than levels for the CON and SAT diets. Concentrations of DNA for total bacteria, A. lipolytica, C. proteoclasticum and S. dextrinosolvens were similar for all diets. The concentrations of B. fibrisolvens (69.1 pg/45ng total DNA) and R. albus (1.96 pg/45ng total DNA) were least with the FO diet but were similar among the other treatment diets (SAT-104.2; 5.4, SBO-121.2; 5.71, and CON-126.3; 5.17 pg/45ng total DNA). S. ruminantium DNA concentration was highest with the FO diet and was least with the SAT diet (177.5, 54.9, 75.5, and 691.1 pg/20ng total DNA for treatment diets 1 to 4, respectively). In conclusion, SBO had no effect on bacterial DNA concentrations tested in this study and the inhibitory effects of FO on BH may be due in part to its influence on B. fibrisolvens, R. albus and S. ruminantium