Abstract
Simple SummaryThere are several substances, either inorganic or organic that may be toxic for sheep. Intoxications by some of these substances have an acute clinical course with specific signs and lesions that may guide the diagnostic procedures. However, there are other insidious, subacute to chronic presentations, usually related to continuous intake of the toxic substance over long periods of time, that may present with emaciation, ill-thrift, and/or poor external aspect. In such scenarios, diagnosis may be challenging and should be achieved through a combination of history of exposure, subtle gross and histological findings (if present), and available ancillary tests.Infectious and parasitic agents have been frequently associated with debilitating and wasting conditions in sheep. The prevalence of these agents has probably undermined the role of toxic causes as contributors to such disorders. In addition, many of these intoxications frequently produce acute clinical disease with specific and characteristic lesions, thus a causal relationship with the toxic substance may be relatively easy to establish. However, persistent exposure to some of these organic or inorganic toxic substances may lead to emaciation, ill-thrift, and poor external aspect. The anti-nutritional factors and alkaloids of several plants, including pyrrolizidine alkaloids, among others, have also been associated with emaciation and/or poor general performance in sheep flocks. In this review, some of these disorders are discussed with an emphasis on clinical signs and lesions, relevant diagnostic aspects, and available therapeutic approaches. In most cases, demonstrating a history of exposure should be one of the most relevant aspects of the diagnostic approach, and removing the animals from the toxic source is the cornerstone of the majority of the treatment strategies.
Highlights
There are several diseases of sheep that may cause wasting, leading to decreased productivity and economic losses in sheep flocks as a result
We review conditions caused by inorganic and organic toxic compounds and some poisonous plants, with an emphasis on clinico-pathologic and diagnostic aspects, and we analyze their contribution to wasting, debilitation, and/or loss of productivity in sheep
Sheep may show no clinical abnormalities before the hemolytic crisis occurs, in certain cases there could be an elevation of hepatic enzymes such as plasma aspartate transaminase (AST) and gamma-glutamyl transferase (GGT), with anorexia and ill-thrift prior to this crisis [6,10]
Summary
There are several diseases of sheep that may cause wasting, leading to decreased productivity and economic losses in sheep flocks as a result. Johne’s disease, maedivisna, caseous lymphadenitis, and several parasitic diseases, amongst others, have been traditionally included under the umbrella of the so-called “thin ewe syndrome”, a concept that encompasses several diseases with wasting as the main clinical sign [1,2,3,4] This concept has included mostly infectious and parasitic disorders, probably underestimating the role of other disease causes. Certain plants, including grasses, legumes, and shrubs, contain anti-nutritional and toxic compounds that, depending on the situation, may cause deleterious effects on animals that consume them [7,8]. Some of these substances are non-lethal, but their consumption during long periods of time, especially with concomitant confinement and/or food scarcity, may lead to emaciation as well. We review conditions caused by inorganic and organic toxic compounds and some poisonous plants, with an emphasis on clinico-pathologic and diagnostic aspects, and we analyze their contribution to wasting, debilitation, and/or loss of productivity in sheep
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