Summary The geographical distribution of bovine leukaemia‐virus (BLV)‐infected herds in Costa Rica and the isolation of BLV from cases of enzootic bovine leukosis are presented. It was found that BLV is prevalent throughout the country, affecting mostly dairy cattle (Bos taurus) located in the highlands around the central valley of Costa Rica. By contrast, beef cattle (Bos indicus) raised in the lowlands were affected to a lesser extent. One out of four isolates of BLV obtained from local cattle with lymphosarcomatous tumours was analysed and had similar physical, serological and biological characteristics to a reference strain of BLV isolated in the USA. However, different patterns of recognition of BLV‐protein p24 were observed among naturally infected cattle using the western‐blotting technique.

The aim of this study was to assess the relationships of hepatic triacylglycerol (TAG), plasma glucose, plasma cholesterol, and plasma urea nitrogen (PUN) concentrations with the morphological quality of oocytes obtained from 20 Carora breed lactating cows at days 20 and 35 postpartum in a commercial farm. Oocytes were obtained through the technique of transvaginal ultrasound-guided follicle aspiration. Change in body condition score (0.35 vs. 0.44, P = 0.02) and mean plasma cholesterol (3.59 vs. 4.35 mmol/L, P = 0.01) significantly differed between the 2 periods, whereas mean TAG tended to be higher at day 35 after calving (2.29 vs. 2.54%, fresh basis, P = 0.06) and indicated moderately fatty liver. At day 35 postpartum, both plasma cholesterol and TAG tended to have a positive correlation with oocyte quality (%), at r = 0.44 (P = 0.08) and 0.40 (P = 0.05), respectively, but no associations between glucose or PUN and oocyte recovery traits were found at any time. The percentage of oocytes with high quality was found higher (86.7 vs. 52%, P = 0.04) in those cows with more than 4 oocytes recovered. In conclusion, there was a positive relationship among hepatic TAG, plasma cholesterol, and quality of oocytes in Carora breed lactating cows.