Poisoning of sheep by seeds of Crotalaria retusa: Acquired resistance by continuous administration of low doses

Abstract

Seeds of Crotalaria retusa containing 6.84% (dry weight) of monocrotaline (MCT) were administered experimentally to sheep. Three sheep that received 136.8mg MCT/kg bw daily for 70 days had no clinical signs. Five out of six sheep ingesting single doses of 205.2 and 273.6mg MCT/kg bw died with acute (three sheep) or chronic intoxication (two sheep). Acute intoxicated sheep had periacinar liver necrosis and chronic intoxicated sheep liver fibrosis and megalocytosis. Another three sheep had no clinical signs after the ingestion of 20 daily doses of 136.8mg MCT/kg, followed by seven doses of 273.6mg MCT/kg, and one single dose of 342mg MCT/kg. These experiments demonstrated that sheep are susceptible to acute intoxication by MCT being intoxicated by a single oral dose of approximately 205.2mg/kg. In contrast, they develop strong resistance to MCT after the daily ingestion of non lethal doses (136.8mg/kg). It is suggested that chronic poisoning does not occur by the repeated ingestion of non acutely toxic doses, but probably by the ingestion of single toxic doses. It is also suggested that sheep do not become intoxicated with the ingestion of C. retusa in the vegetative non-seeding stage.

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

“…These results confi rm that repeated nontoxic doses of monocrotaline induce resistance to the poisoning of sheep exposed to seeds of C. retusa as demonstrated by ANJOS et al (2010). However, the present study indicates that this resistance is of short duration, between 7 and 15 days after cessation of the non-acutely toxic exposures.…”

“…Considering the results of this and previous work (ANJOS et al, 2010;RIET-CORREA et al, 2011) resistant sheep can be used for the biologic control of C. retusa provided that the rapid loss of resistance is taken into account. Because leaves of C. retusa contain concentrations of MCT, from 0.16% to 0.5% (NOBRE et al, 2004(NOBRE et al, a,b, 2005 they are much less toxic than the seeds.…”

“…Recently it was demonstrated experimentally that sheep are susceptible to acute intoxication by monocrotaline (MCT)-containing C. retusa seeds and can be poisoned by a single oral dose of seeds equivalent to about 205mg MCT per kg of body weight (mg kg -1 ), but they develop a resistance to these acutely lethal oral doses after the daily continuous ingestion of non-toxic dose of seeds equivalent to about 136mg MCT kg -1 (ANJOS et al, 2010). In a recent outbreak of acute intoxication, 34 out of 150 sheep died in a pasture invaded by C. retusa in seed set.…”

Estudo sobre a sensibilidade dos caprinos à toxidez de crotalárias tóxicas para bovinos visando a sua utilização na profilaxia

“…Os achados clínicos, macro e microscópicos do Caprino 2 na intoxicação experimental por C. spectabilis foram compatíveis com o que já havia sido relatado na intoxicação natural e experimental por C. spectabilis em suínos (Torres et al 1997, Ubiali et al 2011) e na intoxicação natural e experimental de caprinos e ovinos por C. retusa (Anjos et al 2010, Nobre et al 2005, Riet-Correa et al 2011, Maia et al 2013. A evolução e os achados microscópicos devem ser diferenciados de outras causas de necrose hepática na espécie caprina, em especial da intoxicação por plantas hepatotóxicas agudas, como Cestrum laevigatun e Trema micranta (Tokarnia et al 2012).…”

“…As lesões hepáticas, macro e microscópicas observadas no Caprino 4 foram semelhantes às descritas na intoxicação experimental crônica de suínos por C. spectabilis (Souza et al 1997, Torres et al 1997) e na intoxicação crônica natural e experimental de ovinos por C. retusa (Nobre et al 2005, Anjos et al 2010, Riet-Correa et al 2011.…”