Identification of lamb flocks susceptible and resistant against Brachiaria poisoning

Abstract

This study was designed to assess the influence of genetic resistance against brachiaria poisoning in sheep. Two groups of sheep, one identified as susceptible (formed by two ewes and one ram) and the other as resistant against brachiaria poisoning (formed by three ewes and one ram) were selected. Sheep considered susceptible were those that presented clinical signs of brachiaria poisoning at any time of their life; resistant sheep were those that even raised on Brachiaria spp. pastures, did not developed any sign of the poisoning during their life. The offspring of the two flocks (15 lambs from the sensitive flock and 9 lambs from the resistant flock) were placed into brachiaria pasture (initially Brachiaria decumbens and B. brizantha,and only B. decumbens after weaning) and followed up during two years (2013)(2014). The determination of protodioscin levels in B. decumbens pasture was performed only in 2014 and revealed significant amounts of the toxic principle. Eleven lambs of the susceptible group were affected to some degree of brachiaria poisoning and six died; no lamb of the resistant group was affected. Clinical signs consisted of varying degrees of subcutaneous edema of the face and, erythema and loss of hair of the ears, crusts on the skin of ears, around the eyes and on planum nasale, scar deformation of the ears, and bilateral ocular discharge; affected lambs also sought for shadowy shelters and they were poor doers. Several sheep recovered from the condition and then relapsed. Necropsy findings in six lambs included pale mucous membranes, emaciation, dermatitis, scar deformation of the ears, large yellow livers with marked lobular pattern, and moderate infestation by Haemonchus contortus. Histologically the liver lesions were similar in all necropsied lambs but with varying degrees of severity; they were consistent with brachiaria poisoning and included architectural disruption of hepatocellular trabecula, clusters of foamy macrophages occasionally forming multinucleated giant cells, swollen and vacuolated hepatocytes, crystals or negative images of crystals in the biliary system, bilestasis, bile duct proliferation and lymphoplasmacytic infiltrate in portal triads. The skin lesions were those of photodermatitis and included epidermal necrosis, hyperkeratosis and dermal neutrophilic infiltrate. The results of this study allow to conclude that there is a genetic related resistance to brachiaria poisoning in sheep since the progeny of resistant sheep did not manifest the poisoning.

Poisoning by Brachiaria spp. in various lamb breeds at increasing levels of supplementation during growth

“…The concentrations of protodioscin (1.59±1.33%) were similar to those previously considered toxic for lambs. Concentrations ranging from 0.74 to 2.56% have been reported in weaned lambs (Mustafa et al 2012, Pupin et al 2016 and from 0.62 to 1.15% in suckling lambs (Melo et al 2018). MS = mineral supplementation, 0.8% EPS = lambs receiving 0.8% bw EPS, 1.6% EPS = lambs receiving 1.6% bw EPS, 2.4% EPS = lambs receiving 2.4% of bw EPS, b age at onset of clinical signs, c onset of clinical signs after the start of the experimental period (after weaning), d bw = body weight.…”

“…The expected lesions for determining poisoning in the lambs were restricted to specific sites of non-pigmented skin, mainly in the face and ears. Clinical signs consisted of edema, alopecia, erythema, formation and detachment of scabs, apathy, anorexia, jaundice, and weight loss (Mustafa et al 2012, Porto et al 2013, Pupin et al 2016, Melo et al 2018.…”

“…Poisoning by these grasses, however, causes direct and indirect losses in sheep flocks (Mustafa et al 2012, Porto et al 2013). Outbreaks have been described in weaned lambs in the growth phase (Riet-Correa et al 2011, Mustafa et al 2012, Pupin et al 2016 and in suckling lambs (Melo et al 2018), demonstrating that these categories are more vulnerable than others, being susceptible to poisoning from the beginning of the consumption of the forage (Melo et al 2018).…”

“…The influence of genetics on the sensitivity to poisoning (Pupin et al 2016, Castro et al 2018 indicates that the selection of animals genetically resistant to poisoning is an efficient means of prevention. This selection, however, is a slow process, because methodologies for the identification of resistant animals have not been defined.…”

Weaning Age of Lambs Creep-Fed While Grazing on Marandu Pasture

“…Photosensitization occurred in only a few animals probably due to greater predisposition or resistance to this illness. According to Pupin et al (2016), sheep may have genetic factors that make them resistant to intoxication by Urochloa spp. and thus not manifest these problems.…”