Heat-related Injury in Lambs

The broad spectrum of heat-related injury (HRI) and its associated lesions is well described in the human literature, with rare reports of similar findings in farm animals. In the current case series, lesions from 4 of 8 lambs that presented with clinical signs of heat stress are reported. Gross lesions at necropsy consisted of acute renal swelling and pallor in 2 of 4 lambs, muscle pallor in 2 of 4 lambs, and chronic bronchointerstitial pneumonia in each of the 4 lambs. Histological lesions considered heat-related included acute renal tubular necrosis, pigment casts, tubular epithelial regeneration, multifocal myocyte degeneration, necrosis, and dropout with histiocytic influx and regeneration. Chronic, bronchointerstitial pneumonia, present in each lamb, was considered a condition predisposing to HRI. Compatibility between observed lesions and those reported in human beings with injury secondary to elevated body temperatures established a diagnosis of HRI in these animals. Diagnostic pathologists should consider HRI in lambs with histological evidence of renal tubular necrosis and/or rhabdomyolysis and even in cases where the clinical picture is strongly suggestive but lesions are not demonstrable.