Rumen protozoa of different ages of beef cattle raised in tropical pastures during the dry season

The purpose of this study was to quantify, identify and compare the protozoa populations in the rumen of different ages of beef cattle raised in tropical pastures during the dry season. We sampled the ruminal fluid of 36 steers, 34 cows and 30 calves, all crossbred Nelore. The ruminal fluid was diluted in 10% formaldehyde solution and decimal dilutions were prepared in saline solution to quantify small, medium and large protozoa in Sedgewick Rafter chamber. A total of 135,800 protozoa were evaluated in an optical microscope using Lugol's iodine coloration and the genera were classified according to the morphological characteristics. Total protozoa populations were significantly lower in calf samples. The average of small protozoa population was higher than that of other protozoa groups while the large ciliate population was lower. Protozoa belonging to 17 different genera were identified, showing diversity in this ecosystem. Charonina spp. was the most frequent for both bovine groups. Entodinium spp. was more prevalent in adult cattle and while Buetschilia spp. was more prevalent in calves. In this study, a considerable population of ruminal ciliates presenting high diversity was observed in cattle raised on tropical lignified pastures and their genus profile varied according to the ages of the animals.