Abstract
Prepuberal gilts about 180 days of age were injected with 750 iu pregnant mare serum gonadotrophin (PMSG) and 500 iu human chorionic gonadotrophin (HCG) or 0.1 mg synthetic luteinizing hormone releasing hormone analog (LHRH-A) at 72 h interval (method A or C), or with mixed 400 iu PMSG and 200 iu HCG (method B) to compare the effect of methods for the induction of estrus, ovulation and subsequent fertilization after an artificial insemination at 98 h from the initiation of treatment.The effect of 10 mg estriol (ET) injection to each treatment above mentioned, given at 88 h from the initiation of treatment was also investigated (method A', B' and C').
All the treated gilts, 27 in total, showed red colouring and swelling of vulva which reached its maximum about 92 h to 100 h from the initiation of treatment. Standing reflex was not induced effectively, induced in only 30% of the gilts, and a pars of semen was frequently discharged from the vulva at the time of insemination. By ET injection the vulval reaction was augmented but retained longer and not so effective for the induction of standing reflex.
When the gilts were killed at 141 h from the initiation of treatment, ovulation was induced in all the gilts except for two gilts by method B' where the ovulation appeared to be delayed by ET injection. Number of follicles ovulated was comparatively moderate (mean no. 8.6) but variable and did not differ significantly by the methods.
Eggs were recovered quite efficiently from the oviducts of gilts treated by method A, B and C (96% to 100%), but less efficiently from the gilts after ET injection (50% to 62.5%). Fertilized eggs were recovered from 80% of gilts ovulated. The failure of fertilization in the others was considered not to be due to the methods used, but mainly attributable to the delayed ovulation from unknown reason. The fertilization rate of recovered eggs did not differ significantly by methods (overall mean 64.5%) except for those of method A where the rate was significantly higher (82%). However, the stage of development of fertilized eggs was significantly different by the methods used; the most advanced stage (61.4% were of cleaved) by method C and C', the middle stage (35.4% were of cleaved) by method A and A', and the delayed stage (all at pronuclear) by method B. This difference suggests that there may be subtle difference of ovulation time by induction methods used and careful choice of the timing of insemination may be necessary.
Whether normal estrus can be cycled after the induced ovulation and whether high conception rate and normal range of litter size can be obtained are now under investigation.
