ASPIRATION OF THE DOMINANT FOLLICLE IN MARES AND ITS EFFECT ON SUBSEQUENT FOLLICULAR DEVELOPMENT

An attempt was made to increase the number of small- and medium-sized follicles present for ultrasound-guided oocyte recovery by aspirating the dominant follicle prior to its inhibition of growth of other folli cles. Cyclic mares were randomly assigned to one of four groups on day of ovulation. Each mare was examined daily with ultrasound beginning 8 days after ovulation to determine growth and regression of individua l follicles at least 15 mm in diameter, Once a dominant follicle was i dentified, the dominant follicle in Group 1 mares was aspirated and al l other follicles (at least 15 mm) aspirated 3 days later; the dominan t follicle in Group 2 mares was identified but not aspirated and all f ollicles (at least 15 mm) aspirated 3 days later; the dominant follicl e in Group 3 mares was aspirated and all other follicles (at least 15 mm) aspirated 6 days later; and the dominant follicle in Group 4 mares was identified but not aspirated and all follicles (at least 15 mm) a spirated 6 days later. A dominant follicle was defined as the largest follicle present for 2 consecutive days beginning 8 days after ovulati on. Identification did not occur until the dominant follicle was at le ast 25 mm in diameter, The dominant follicle was identified 15.1 +/- 3 .4 days after ovulation. Mean number of small (3-17 mm) and medium (18 -27 mm) sized follicles 3 or 6 days after identification/aspiration of the dominant follicle were similar among all treatment groups (P > 0. 05). Mares in Group 2 had a greater (P < 0.05) number of large follicl es (at least 28 mm) 3 days after identification of the dominant follic le than Group I mares (1.3 vs. 0.5, respectively); means for Groups 3 and 4 were similar. Based on linear regression slopes of growth patter ns for individual follicles, a higher rate of atresia occurred in subo rdinate follicles within 6 days following identification, but no aspir ation of the dominant follicle (- 0.63 mm day(-1)), than for those fol licles present following aspiration of the dominant follicle (-0.10 mm day(-1) P < 0.05). A greater percentage of follicles were growing (slope) after aspiration of the dominant follicle (47/137 or 34.3%) tha n those follicles present without