Dermatite por farelo de arroz desengordurado e outras doenças de pele diagnosticadas em bovinos na Região Sul do Rio Grande do Sul

Abstract

Defatted rice bran (DRB), a byproduct of rice processing, has been used in the feeding of dairy and beef cattle. However, cases of poisoning by this food, with skin lesions observed on the limbs and attributed to type I hypersensitivity, have occurred in Brazil and Uruguay. The objectives of this thesis were to experimentally reproduce DRB poisoning in cattle; to prove its allergic character, its pathology and its pathogenesis with a view to indicating its use in animal feed in an efficient and safe manner. The aim was also to conduct a retrospective study of spontaneous cases of DRB poisoning diagnosed in Laboratório Regional de Diagnóstico da Faculdade de Veterinária da UFPel (LRD/UFPel). In addition to this, a retrospective study was also carried out on the main skin diseases that affect cattle in the area of influence of the LRD/UFPel, establishing their importance in the southern region of Brazil. For the experimental reproduction of DRB poisoning, it was administered to 12 cattle divided into three groups, in quantities of 0.5%, 1.0% and 2.0% of the body weight of each cattle, until they presented lesions. Blood was collected from the cattle for hemogram and IgE dosage. The macroscopic lesions observed in cattle that received 1.0% and 2.0% DRB were characterized by hyperemia with alopecia and edema in the fetlock region that evolved into an ulcerated lesion, with thickening and dryness of the skin, cracks and crusts. The histological lesions observed in biopsies were characterized by marked diffuse subacute hyperplastic dermatitis. The IgE dosage showed inconclusive results and the blood counts were within normal parameters. In the retrospective study, four outbreaks of the disease were identified with lesions characterized by proliferative dermatitis similar to the lesions of the experimental cases. It is concluded that DRB, under the conditions of this experiment, could be administered in a controlled manner to cattle in doses up to 0.5% of the animals' body weight. The administration of DRB in alternating periods with intervals of at least 15 days would also be a way of using this food without the risk of the disease occurring. In the study of skin diseases in cattle, it was concluded that those of an infectious and/or inflammatory nature, such as dermatophilosis, papillomatosis and dermatophytosis, represented more than half of the cases of dermatopathies diagnosed in cattle and are the cause of economic losses for livestock in the region.