Hepatogenous Photosensitization Neonatal Calf Raised on Brachiaria decumbens Pasture

Abstract

Background:  Hepatogenous photosensitization occurs when there is a liver injury that prevents the excretion of phylloerythrin, which absorbs solar radiation, leading to the release of free radicals, which result in cellular damage. Lithogenic saponins present in grasses of the genus Brachiaria spp. are capable of inducing the formation of bile crystals, leading to hepatogenic photosensitization. Lactating animals can develop the condition when ingesting breast milk containing saponins. This study aims to report the diagnosis, clinical evolution and treatment of a case of hepatogenic photosensitization in a 22-day-old lactating Tabapuã calf.

Case: The animal was raised with its mother on pasture composed exclusively of Brachiaria decumbens. Physical examination revealed skin erythema, yellowish diarrhea, corneal opacity and corneal ulcers in both eyes. The animal presented alopecic and reddish areas on the back, flanks, rump, limbs and face. Upon manipulation, the fur and skin came off, revealing a reddish subcutaneous layer. Among the laboratory tests requested, the blood count showed leukocytosis due to lymphocytosis and hyperfibrinogenemia. The results of the egg and oocyst count per gram of feces, the hematozoan test and the skin scraping were negative. The presumptive diagnosis of hepatogenic photosensitization was based on the anamnesis and clinical signs and later confirmed by the response to the established treatment measures. Treatment consisted primarily of removing the mother and calf from the Brachiaria decumbens pasture and from exposure to sunlight. Vitamin and amino acid complexes, anti-inflammatory drugs and antibiotics were also used. To treat the corneal ulcers, it was necessary to use several ophthalmic drugs, the dosages of which had to be adjusted during treatment. In addition, 2 subconjunctival injections of 0.2% meloxicam were performed in both eyes, and a grid keratotomy procedure was performed. After complete healing of the ulcers, dexamethasone ophthalmic ointment was used to reduce scarring. After 54 days of treatment, the calf showed complete remission of clinical signs, with re-epithelialization and significant hair growth in the affected areas.

Discussion: The study reports a case of a lactating calf, so the ingestion of toxins occurred via breast milk. The mother was raised on Brachiaria decumbens pasture, a species with high concentrations of lithogenic saponins. Clinical signs included corneal ulcers, a condition rarely reported in cases of hepatogenic photosensitization. The calf is a Tabapuã breed, with more pigmented skin, showing that even dark-skinned animals can develop severe forms of the disease. The main treatment measures are changing the animal's diet and removing it from direct sunlight. In this case, since it is a lactating animal, the mother needed to change its diet in order to stop the transfer of toxins via milk. Prevention and control measures should be considered in cattle affected by the disease. Strategies such as gradual adaptation to pasture and nutritional supplementation can reduce the risk of poisoning. In addition, reproduction of the affected animal and the use of Brachiaria spp. species with lower concentrations of saponins can be avoided. It is important to consider the occurrence of the disease in lactating animals when considering possible diagnoses. Clinical and epidemiological knowledge, early diagnosis and rapid intervention are crucial for a good prognosis of the disease.

Keywords: beef cattle, intoxication, tabapuã, neonate.