Ciatostomíneos (NEMATODA, CYATHOSTOMINAE): comportamento de larvas em Brachiaria humidicola e depleção energética, em clima tropical, Rio de Janeiro, Brasil

Abstract

Aiming to expand knowledge of the biology and epidemiology of pre-parasitic stages of equine cyathostomin and contribute to the development of control programs that reduce the use of anthelmintics, this study examined the period from July 2007 to September 2008 the following items: 1 - the transmission of infective larvae of cyathostomin on Brachiaria humidicola at 8 and 5 p.m. in different seasons; 2 - the availability of L3 in B. humidicola in two heights, base: 0-10cm and top: 10 - 20cm and 3 - from December 2009 to November 2010, the depletion energy of larval cyathostomin in the seasons. The experiment were developed at Laboratório de Helmintologia da E.P.P. W.O.Neitz, do Dep. de Parasit. Animal da UFRRJ, located at 22º41' South latitude, 43°41' west longitude, altitude 33m and climate classified as AW-tropical humid. Feces were collected directly from the rectum of horses naturally infected and deposited at the beginning of each season, in plots with the grass B. humidicola. The Baermann technique was used for recovery of L3 from faeces and pasture. After recovering from larvae and feces samples of grass were maintained for 48 hours at 75 º C, to obtain the dry matter. For the first step, the fecal mass was divided into two samples of 500g each and deposited on grass B. humidicola in the beginning of each season. From each sample, weekly, an aliquot of grasses and feces was collected at 8a.m. and 5 p.m. In spring and winter, the smallest amount of rain and mild temperatures contributed to the survival and transmission of L3 to the ragweed. In rainy months, covering the summer and autumn, there was a lower prevalence of L3 in the stool sample and grass. In the second step, to start each period, four samples of 500g were placed in grass and seven days after deposit and fortnightly, samples of feces and grasses were collected at 8am. The number of larvae recovered was higher in the dry season. Larvae were present in the pasture during the entire period of experiment, demonstrating the risk of infection for animals raised in the field and the need for new management strategies. To perform the third step, the beginning of each season, collected stool samples were homogenized and divided in 360 stool cultures (60/treatment). Energy depletion of the larvae was analyzed based on the technique of Pinheiro and Gomes (1994) using larvae with 7, 15, 30, 45 and 60 days-old. In summer and autumn, the verified amount of glycogen did not change (0.27 and 0,28 mg glucose / g tissue Fresh Weight, respectively). A spike in the amount of glucose was observed at 30 days of life in all seasons. The smallest amount of glycogen was measured in winter (0.09 mg). In the spring we obtained 0.22 mg. The pasture is a vehicle of infection for the animal throughout the year, especially during the colder seasons, when the period of survival of larvae on pasture is greater, which results in greater energy expenditure.