Intoxicação experimental aguda por Senecio brasiliensis em ovinos e indução de resistência à intoxicação

Abstract

ABSTRACT.-Grecco F.B., Estima-Silva P., Marcolongo-Pereira C., Soares M.P., Rafϐi M. Sheep are more resistant to poisoning by Senecio spp. than cattle and horses. To determine whether this resistance could be induced by ingestion of small and repeated doses of the plant and to know how long the resistance could last, three experiments with fresh green leaves and stalks of Senecio brasiliensis were conducted. In Experiment 1, to determine the minimum dose for acute poisoning, single doses of 60, 80, 90, 100 and 100g/kg body weight (bw) were administered to ϐive 1 and a half-year-old male Corriedale sheep. The sheep fed 60g/kg bw and 80g/kg bw of S. brasiliensis did not get sick; however, the sheep that received 80g/kg bw, developed mild ϐibrosis and megalocytosis in liver biopsies performed 90, 120 and 150 days after the end of plant administration. The sheep that received 90 and 100g/kg bw showed clinical signs of anorexia, prostration, paddling movements and abdominal pain, and died 12-48 hours after the onset of clinical signs. At their necropsy, ascites, disseminated petechiae and accentuated lobular pattern of the liver were found, and histologicaly hemorrhagic centrilobular necrosis was observed. In Experiment 2, the dose of 100g/kg bw fractionated into 2, 5 and 10 daily doses was administered to three sheep respectively. The fractioned dosage did not cause clinical signs of poisoning in any of the sheep, but periportal ϐibrosis and moderate megalocytosis were observed in liver biopsy performed at day 60 after the end of the plant administration. No histological lesions were observed in hepatic biopsies of sheep that received 10 daily doses of 10g/kg bw. In Experiment 3, to determine whether the sheep become resistant to the acute form of poisoning, four sheep ingested daily doses of 15g/kg bw of S. brasiliensis during 30 days and daily doses of 30g/kg bw for 10 days. On the day following the last dose of 30g/kg bw, two sheep were challenged with 100g/kg bw of the plant in a single dose. No clinical signs were observed in both sheep and no histological lesions could be found in the liver biopsies obtained 15 and 30 days after administration of the challenge dose. The third and fourth sheep received the challenge dose (100g/kg bw) 15 and 45 days after the end of plant administration. These animals showed anorexia, abdominal pain, and died about 12 hours after the onset of clinical signs. Gross and microscopic lesions were similar to those observed in sheep from Experiment 1. The results of this study demonstrate that sheep are susceptible to acute S. brasiliensis poisoning at doses of 90 and 100g/kg bw, but they beco-1 Recebido em 23 de fevereiro de 2012.Aceito para publicação em 8 de junho de 2012.

Duration of an induced resistance of sheep to acute poisoning by Crotalaria retusa seeds

“…Similar results were observed with leaves and stems of Senecio brasiliensis in sheep that received daily non-toxic doses of 15g plant material kg -1 for 30 days and 30g plant material kg -1 for another 10 days. The sheep challenged at the end of the administration period were resistant to an acute toxic dose but those challenged 15 and 45 days post the resistance induction regime succumbed to an acutely toxic dose (GRECCO et al, 2012).…”

Experimental poisoning in broiler chickens by Senecio vernonioides, Senecio conyzaefolius and Senecio paulensis

“…Pilati & Barros (2007) also provided a single S. brasiliensis dose of 15g/kg to an equine that demonstrated neurological symptoms. Grecco et al (2012) provided S. brasiliensis at a single dose of 60g/kg to sheep that showed no clinical signs or microscopic changes, demonstrating the resistance of this species to the single dose of the plant.…”

Importância econômica, epidemiologia e controle das intoxicações por plantas no Brasil

“…Foi demonstrado, também, que animais que adquirem esta resistência a perdem rapidamente, em pouco mais de uma semana (Maia 2013). Uma situação semelhante ocorre com Senecio brasiliensis em ovinos que ingerindo diariamente doses não tóxicas continuadas adquirem resistência a doses tóxicas (Grecco et al 2012). A ingestão de pequenas doses consecutivas de favas de Enterolobium cotortisiliquum também induz resistência (Tokarnia et al 1999) e permite que ovinos e caprinos que permanecem em áreas onde ocorre a planta, ingerindo as favas, durante todo o período de frutificação, sem apresentar sinais clínicos (Riet-Correa F., dados não publicados).…”