Changes in follicular populations following treatment of buffaloes with PMSG (eCG) and Neutra-PMSG for superovulation

Abstract

Some 19 buffaloes were synchronized by administration of a prostaglandin (PG) salt Lutalyse, with a single intramuscular (i.m.) injection of 25 mg at day -13. Luteolysis was induced by administration of 50 mg PG, in divided doses of 30 and 20 mg i.m. 12 h apart on day 0 of experiment. The 30 mg PG injection was designated as 0 h of experiment. Group I animals (n = 6) received saline and served as controls while animals in Groups II (n = 7) and III (n = 6) received 2500 I.U. PMSG (eCG) i.m. at day -2. Group III animals were administered 5 ml Neutra-eCG intravenously at 60 h. The number of follicles, classified on the basis of diameter as small (2-5 mm), medium (6-9 mm) and large (> or = 10 mm) was assessed by ultrasonography on days -2, -1, 0, 1, 2, 5 and 7 of experiment. The number of corpora lutea (CL) was recorded by palpation per rectum on day 8. The number of small follicles which did not differ among the three groups on days 0, 1 and 2 was significantly lower (P < 0.05) in Group II animals compared to those in Groups I and III on days 5 and 7. The number of medium follicles increased after eCG treatment and was significantly higher (P < 0.05) in animals of Groups II and III on days 0 and 1, compared to control animals of Group I. It was, however, not different among the three groups on subsequent days of experiment. The number of large follicles which did not differ among the three groups on days -2, 0, 1 and 2 was significantly higher in Groups II (P < 0.01) and III (P < 0.05) animals compared to those of Group I on day 5. On day 7, the number of large follicles was in the order (P < 0.05) Group II > Group III > Group I. The number of CL in Group II animals was significantly higher (P < 0.05) than that in Group I animals but was not different from that of Group III animals. These results suggest that treatment of buffaloes with eCG for superovulation reduces the number of small follicles and increases the number of large follicles 5-7 days after PG treatment. Administration of Neutra-eCG 60 h after PG treatment can partly reverse this trend but has no effect on ovulation rate. The possibility that part of the variability in ovulation rates in this study may have resulted from Neutra-eCG been given prior to or at the LH surge, or from the absence or presence of a dominant follicle at the time of eCG treatment cannot be ruled out.