Abstract
The objective of this study was to determine effects of age and castration on follicle stimulating hormone (FSH) secretion in prepuberal heifers. In experiment 1, twelve heifers were bilaterally ovariectomized at 3, 6, or 9 months of age (n = 4/group). Blood was collected at 10 min intervals for 8 hr at 1 week before ovariectomy and 1 and 4 weeks after ovariectomy. Frequency, amplitude and duration of FSH pulses were calculated. Mean plasma concentration of FSH (ng/ml), and frequency (pulses/8 hr), amplitude (ng/ml), and duration (min/pulse) of FSH pulses were not altered by age. Mean concentration of FSH increased (P<.01) from 1 week before to 1 week and 4 weeks after ovariectomy, respectively, in all age groups. Pulse frequency increased (P<.05) from 1 week before ovariectomy to 4 weeks after ovariectomy in 3 month old heifers. Pulse amplitude of FSH increased (P<.01) from 1 week before to 1 week after ovariectomy in 3 month old heifers, from 1 week before to 4 weeks after ovariectomy in 6 month old heifers, and from 1 week before to 1 week and 4 weeks after ovariectomy in 9 month old heifers. In experiment 2, twelve heifers were bilaterally ovariectomized at 3, 6 or 9 weeks of age (n = 4/group). Sample collection and measurement of mean concentration of FSH were the same as in experiment 1. Mean concentration of FSH increased (P<.01) from 1 week before to 1 and 4 weeks after ovariectomy in heifers ovariectomized at 6 and 9 weeks of age. Mean concentration of FSH increased (P<.01) from 1 week before to 4 weeks after ovariectomy in heifers ovariectomized at 3 weeks of age and was increasingly higher (P<.05) in heifers ovariectomized at 3 to 6 to 9 weeks of age. Thus, ovarian inhibition of FSH secretion is established in Holstein heifers ovariectomized at 9 weeks of age and maintained through 9 months of age.
Published Version
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