Effect of starch-based supplementation level combined with oil on protozoa population of young Nellore steers grazing tropical pasture during rainy season

Ciliate protozoa play a vital role in rumen fermentation, once that exert a protection of easily fermentable carbohydrates from sugar-/starch-utilizing bacteria so that organic acids are not produced in plenty immediately after the feeding of animals. The objective of this study was evaluate the effect of oil supplementation combined with high- or low-starch on protozoa population of young Nellore steers grazing Brachiaria brizantha cv. Xara?s during the growing phase. Eight ruminal cannulated Nellore steers (424.8 kg ? 35.5) at 20 mo of age were used in a replicate 4 x 4 Latin square with a 2 x 2 factorial arrangement of treatments (high or low starch, with or without a source of oil), experimental period of 21 days. The animals were allocated into 4 paddocks of 0.25 ha each, consisting of Brachiaria brizantha cv. Xara?s. The supplements were corn combined with SG (soybean grains); corn without SG; SH (corn or soybean hulls) combined with SG; and SH without SG. Animals were supplemented at the rate of 0.5% BW, daily, at 1000 h, in a par of feed bunks arranged in each paddock, and had ad libitum access to water. Ruminal microbiology samples were collected on the d 18, after 3 h of supplementation (1000 h). For the population cell counts of protozoa were obtained from rumen content aliquots that were preserved in formalin. Each sample was homogenized and 1mL of ruminal content was pipetted and transferred to vials with lugol. To quantify the protozoa, from each vials was pipetted 1mL of content to fill the chamber of Sedgewick-Rafter. There were no interactions between starch level and oil supplementation on numbers of Dasytricha (P = 0.89), Isotricha (P = 0.26), Polyplastron (P = 0.33), Ostracodinium (P = 0.26), and total protozoa (P = 0.93). However, there was interaction between starch and oil supplementation on Entodinium population (P = 0.04). Animals supplemented with high-starch and without oil showed greater numbers of Entodinium than the other supplements. In addition, independently of starch level utilized, oil supplementation decreased the numbers of Dasytricha (P < 0.01), Isotricha (P < 0.01), and total protozoa (P < 0.01). Supplementation with high starch and oil content can impact the persistence of known order of the Entodinium protozoa, however further studies are necessary.