Toxicity of the different vegetative stages of Amorimia pubiflora to sheep

Abstract

Toxic plants containing monofluoroacetate (MFA) cause sudden death in livestock in Australia, South Africa and Brazil, causing economic losses to producers. The objective of this study was to determine the amount of MFA present in young leaves, mature leaves, senescent leaves, and seeds of Amorimia pubiflora harvested at different times of the year and to determine their toxic effect on sheep. Samples of Amorimia pubiflora were collected during April, August and December of 2015 and March of 2016, separated according to the vegetative stage (young leaves, seeds, mature leaves, and senescent leaves), dried in an oven, and administered in daily doses of 5 g/kg/body weight (bw) of fresh leaves to sheep through ruminal cannulae. The experiment was divided into four stages according to the time of collection of the plant so that each sheep received a different vegetative stage of the plant (young leaves, mature leaves, and senescent leaves). Only in the second stage of the experiment was it possible to collect A. pubiflora seeds, which were administered using the same method used for the administration of the leaves. The sheep were dosed with the plant until they showed clinical signs of toxicosis or until the plant was no longer available. Aliquots of leaves and seeds of A. pubiflora were analyzed for MFA concentration. The seeds and young leaves had higher concentrations of MFA than did the mature (harvested in August and December) and senescent (harvested in December) leaves. However, all vegetative stages of the plant were toxic and caused fatal poisoning. The results of our study showed that A. pubiflora is toxic to sheep even when MFA concentrations are low, demonstrating that the presence of this substance is a risk factor for the occurrence of poisoning. Knowing the toxic principle and its variations allow us to determine the conditions for the occurrence of plant toxicosis as well as possible treatment, control, and prophylaxis methods, contributing significantly to the reduction of economic losses on farms due to plant poisoning.