PLASMA GONADOTROPIN-LEVELS IN INTACT AND OVARIECTOMIZED PREPUBERTAL PONIES

The patterns of gonadotropin secretion were determined for prepubertal female ponies from birth-10 months of age. In experiment 1, LH and FSH were determined for 4 spring-born (April) foals in May through July when the ponies were 3 weeks-3 months old. LH remained low and constant while FSH increased from a low in May and early June to a high in late June through July. In experiment 2, 9 spring-born foals were assigned to either ovarian intact or ovariectomy groups. Ovariectomy was performed on August 16 when ponies were 4 months old. Plasma samples from August through February were assayed. There was no effect of ovariectomy on either FSH or LH and, therefore, ovarian intact and ovariectomized groups were combined. LH remained low and constant throughout the experimental period. FSH decreased from a high during August and September to a low during October through early December. FSH then increased during late December and January; however, mean concentrations of FSH for the summer in intact fillies were higher than during the winter. In experiment 3, gonadotropin profiles were examined for late-born (summer) fillies. For the period from birth-9 days of age, FSH remained low and constant. Mean LH was higher on the day of birth than on any other day assayed. Patterns of FSH secretion for the late-born foals appeared inconsistent when compared with those of spring-born foals.