Perfil epidemiológico da Leucose Enzoótica Bovina em um sistema intensivo de produção de leite.

Abstract

Bovine Leukosis Virus (BLV) is a viral disease that affects cattle and causes significant production losses. In older animals, generalized lymphosarcoma may occur. The objective of this study was to understand the distribution of BLV prevalence in a confined dairy cattle farm in a Compost Barn and some clinical parameters of these animals. For this, a blood sample was collected in a clot activator tube from all the cattle on the farm, and palpation of the superficial cervical and supramammary lymph nodes was performed in 282 animals. In addition, zootechnical data such as milk production, calving interval, age, and animal category were collected, and a visit and inspection were conducted to understand the main risk factors for BLV transmission. The blood in the clot-forming tube was centrifuged, and the agar gel immunodiffusion test (AGID) was performed for BLV. A second blood collection (EDTA) was required for 24 animals, 12 positive for BLV and 12 negative, and a complete blood count, fibrinogen, and total protein were performed. To compare the means, the Student's T-test was performed, and a descriptive analysis evaluated the prevalences. The prevalence found was 65.93% of positive animals for BLV, being 14 calves (31.35%), 26 heifers (36.30%), and 145 cows (87.08%). It is possible to observe that there is high variation when comparing prevalences between categories, being higher as age increases. When comparing the mean age of positive (59.22 months) and negative (46.083 months) animals, the mean of positive animals is higher (p < 0.05), showing that the longer an animal stays in the herd, the higher the chance of being infected with BLV. Positive animals have a lower hematocrit (32 vs. 29, p < 0.05) and lymphocyte count (7,869ᵅ vs. 10.78, p < 0.05) and a higher platelet count (185,416 vs. 243,916, p < 0.05) compared to negative animals. Milk production and calving interval had no noticeable impact on the disease in the study. A high prevalence of 65.93% of BLV was found on the farm, and several factors may be involved in BLV transmission. The number of positive animals with increases in lymph nodes and lymphocytosis drew attention, which are characteristics related to highly transmissible animals.