Effects of inorganic and organic selenium on the fatty acid composition of rumen contents of sheep and the rumen bacteria and ciliated protozoa

• ISe increased the concentration of c9, t11-CLA in rumen content.
• OSe increased the concentration of α-linolenic acid in rumen content.
• ISe more influenced the fatty acid profile of rumen bacteria than ciliates.

The impact of 3 months of daily administration of equimolar doses of inorganic and organic Selenium (Se) on the fatty acid composition of rumen contents and rumen bacteria and protozoa was studied. Twelve sheep were fed a basal diet of meadow hay (1380 g dry matter/sheep) and ground barley grain (450 g dry matter/sheep) containing a background Se concentration of 0.16 mg/kg DM. The sheep were randomly divided into three groups and fed the basal diet only (Control) or identical diets supplemented with inorganic (Na2SeO3; ISe) or organic Se (selenized yeast; OSe) in equimolar amounts of Se of 0.4 mg/kg of feed DM. The fatty acid (FA) profile was determined in the total rumen contents (TRC), bacterial fraction (BF) and ciliated protozoal fraction (PF). In the TRC, supplementation with OSe decreased the concentration of C18:2cis-9, trans-11 (P<0.05) and increased the concentration of α-linolenic acid (C18:3 n3; LNA; P<0.01). In the BF of the ISe group the content of myristic acid (C14:0; P<0.05), palmitic acid (P<0.01) and medium chain fatty acids (P<0.01) were lower, and the content of long chain fatty acids (P<0.05), stearic acid (C18:0; P<0.01), arachidic acid (C20:0; P<0.001) and behenic acid (C22:0; P<0.01) were increased. The OSe increased the concentration of caprilic acid (C8:0; P<0.001), eicosatetraenoic acid (C20:4 n6; P<0.01) and eicosatrienoic acid (C20:3 n3; P<0.01) in the BF. In the PF the ISe decreased the concentration of docosahexaenoic acid (C22:6 n3) and tricosylic acid (C23:0; P<0.05). The addition of OSe increased the content of LNA (P<0.01) and decreased the content of palmitooleic acid (C16:1; P<0.05) in the PF. Our results point to the probable impact of OSe on the intake of dietary polyunsaturated fatty acids (PUFA) by rumen microbes, especially by rumen ciliates, and on the biohydrogenation of PUFA to more saturated FA.