196 COMPARING OOCYTE LIPID CONTENT WITH CIRCULATING CHOLESTEROL AND TRIGLYCERIDE LEVELS OF BOS TAURUS AND BOS INDICUS DONOR COWS

Abstract

Intracellular lipid content has been found to be higher in Bos indicus oocytes compared with Bos taurus oocytes (Ballard et al. 2007 Reprod. Fertil. Dev. 19, 170). The objective of this study was to further determine whether there was a correlation between oocyte lipid content and circulating cholesterol (CHL) and triglyceride (TRG) levels of mature purebred Brahman (BR; n = 11) and English breed (EN; n = 13) beef cows. All donor cows were maintained on the same ration 30 days prior to and during the oocyte collection interval. Oocytes were collected from donors at 30-day intervals (3 replicates/female) by transvaginal ultrasound-guided aspirations. Blood samples were collected to evaluate total circulating CHL and TRG levels just prior to CIDR insertion and again prior to oocyte collection. Follicle-stimulating hormone (Folltropin-V; Bioniche, Belleville, Ontario, Canada) was given twice daily for 3 days in decreasing doses beginning on Day 4 after CIDR insertion, with oocyte recovery on Day 8. The mean number of follicles aspirated/donor and oocytes recovered/donor were 12 and 11 for the BR and 18 and 7 for the EN donors, respectively. Oocytes were matured in TCM-199 with 10% fetal bovine serum + bovine LH and bovine FSH (0.01 U mL^–1). After 20 h, mature oocytes with a visible polar body (BR = 242/391 or 61%, and EN = 170/258 or 65%) were denuded by vortexing in Tyrodes HEPES medium + BSA (0.03 mg mL^–1). Visual color scores (1 = light, 2 = medium, 3 = dark) were then assigned to the oocytes. Buoyancy of mature oocytes was then measured by using a sucrose step-density gradient column prepared with sucrose and Dulbecco's PBS. Results from the sucrose gradients ranged from 23% (high lipids) to 35% (lower lipids). The oocytes were stained with Nile Red and evaluated by fluorescent microscopy. Oocyte images were evaluated by using Scion Image software to calculate the Nile Red units (NRU; higher NRU = higher lipid content). Serum was analyzed (Texas Veterinary Medical Diagnostic Laboratory) for CHL and TRG concentrations. Data were analyzed by one-way ANOVA. There was no difference between visual color scores for oocytes from BR and EN donors. However, BR oocytes had significantly (P < 0.05) lower buoyant density and significantly higher mean NRU scores (32% and 173) compared with oocytes harvested from EN donors (33% and 152), respectively. Serum CHL and TRG levels were both significantly higher (P < 0.05) in the BR donors (150 and 33.2) compared with the EN donors (110 and 25.5), respectively. These results suggest that serum cholesterol and triglyceride levels may be predictive of donor oocyte lipid content.