The response of gilts reared in confinement to exogenous gonadotropin and estradiol benzoate

To examine the effect of housing on the ovarian response to exogenous gonadotropins, 51 crossbred gilts were reared in confinement and assigned to a control or a treatment group at an average age of 212 days. Gilts in the control group were maintained in confinement and those in the treatment group were relocated to pasture lots. All gilts were fed a synthetic progestin for at least 19 days, given 1,000 IU pregnant mare serum gonadotropin (PMSG), checked for estrus and then laparotomized 1 to 5 days after estrus for examination of ovarian morphology. After withdrawal of the synthetic progestin and administration of PMSG, 24 of 26 treated gilts and 24 of 25 control gilts exhibited estrus. Single injections of 1,000 IU PMSG resulted in similar numbers of induced follicles and (or) corpora lutea in teated and control gilts. In the second experiment, 43 gilts reared in confinement were assigned to a control or treatment group at an average age of 180 days. Gilts in the control group were maintained in confinement, while gilts in the treatment group were relocated to pasture lots. All gilts were bilaterally ovariectomized, given .25 mg estradiol benzoate and checked twice daily for estrus. The proportion of gilts exhibiting estrus in the control and treatmet groups was 7 of 22 and 15 of 21, respectively (P < .01). The interval from injection of estradiol benzoate to the first day of estrus did not differ significantly between groups. The results indicate that housing in confinement does not affect the ovarian response of gilts to exogenous gonadotropin but that it may reduce the ability of gilts to respond to marginal levels of exogenous estrogen.