Effect of linoleic acid oxidative compounds on superoxide dismutase activity and bacterial abundance in long-term ruminal cultures

Abstract

Heating sunflower oil promotes peroxidation and leads to a modification of ruminal biohydrogenation of polyunsaturated fatty acids in vitro1. Thus, products generated during heating, like hydroperoxides and aldehydes could, at least in part, be responsible for the observed biohydrogenation modifications, possibly acting on rumen bacteria. The objectives of this long-term ruminal in vitro study were to explore the effect of two aldehydes and one hydroperoxide on ruminal bacterial population, using a quantitative approach by qPCR, and to investigate the response of rumen bacteria to this oxidative stress, by studying the effect of these compounds on rumen superoxide dismutase (SOD) activity. In erlenmeyer flasks, no oxidative product, 30 mg of 13(OOH) c9,t11 C18:2, 10 mg of hexanal, or 10 mg of t2,t4 decadienal (T2T4D) were incubated for 3 or 5 days in 6 replicates, with a fermentative substrate (1 g hay, 0.2 g soybean meal and 0.25 g maize), 40 ml of bicarbonate buffer, and 40 ml of rumen fluid taken from a cannulated Holstein cow before the morning meal. The same quantity of oxidation product and fermentative substrate along with 20 ml of bicarbonate buffer were added every 24h. On the last day of incubation, 60 mg of c9,c12 C18:2 was added to each flask 5h before the end of incubation. Samples were taken for SOD (UV spectrophometry) and bacteria qPCR quantification (kit QIAamp DNA®) analyses. Data were analysed using ANOVA followed by a pairwise comparison (Tukey’s test). Rumen bacterial density was not affected by treatments. SOD activity was only affected by T2T4D in 5 days incubations (7.7 compared to 9.6 UI/ml with control, P<0.01). This suggests that T2T4D affect microbial activity without modifying bacterial number. Further analyses are going on to investigate the relationship between this observed change and biohydrogenation modulation. 1. Privé, F., et al. (2010) Temperature and duration of heating of sunflower oil affect ruminal biohydrogenation of linoleic acid in vitro. J. Dairy Sci. 93, 711-722