Protozoa of the rumen can represent 40% of total nitrogen and 60% of the final product of fermentation and it has cellulolytic activity. This study aimed to quantify and identify the ruminal protozoa populations from steers, raised exclusively on pastures during the dry season in the north of Minas Gerais, Brazil. Samples of ruminal fluid of 36 Nellore steers were collected directly from the rumen immediately after slaughter, during the early, middle or end of the dry season. For protozoa conservation, 1 mL of ruminal fluid was diluted in 9 mL of 10 % formaldehydes solution. Decimal dilutions were made in saline and the counting of small, medium and large protozoa was performed in Sedgewick Rafter chamber. The protozoa concentrations were transformed into log10 (x +1), subjected to variance analysis and the means were compared with Duncan test. The genus frequencies were compared with chi-square test. The concentration average of the total and of small and medium protozoa declined significantly over the course of the dry season; however, alterations in large protozoa concentrations were not detected over the three periods evaluated. A total of 7749 protozoa were identified, belonging to 17 different genera. Charonina spp. and Entodinium spp. had the highest occurrence during the three periods of dry season (P <0.05), suggesting the participation of these ciliates in rumen cattle fed exclusively on tropical pasture during this season.
Cattle; nutrition; protozoa; ruminal juice; semiarid