Influence of unilateral castration and increased plane of nutrition on sexual development of Holstein bulls. III. Endocrine responses.
Pituitary gonadotropic hormones were assayed in 65 Holstein bulls from 7 days to 16 months. Pituitary LH concentration and content at 2, 4, 8 and 16 months increased (P<.01) with age, while FSH content increased with age (P<.01) but was lower in UC bulls at 2, 4 and 8 months and higher at 16 months (A x UC, P<.01) as compared to intact bulls. In five samples of plasma collected at 90-minute intervals, one day each month from 1 to 15 months in 10 of the bulls killed at 16 months, LH concentration and variance changed (P<.01) with age reaching maxima at 4 and 3 months respectively. Plasma testosterone concentration and variance changed (P<.01) with age, reaching maxima at 10 and 9 months respectively. In the other 10 bulls killed at 16 months, assays of plasma collected before and after exposure to a teaser showed that stimulation increased LH by 20 minutes after exposure but LH declined by 60 minutes while testosterone was increased 20 (P<.05) and 60 (P<.01) minutes after exposure.
Barnes
M A
MA
Department of Animal Industries University of Connecticut Storrs, Connecticut 06268 USA.
Longnecker
J V
JV
Riesen
J W
JW
Woody
C O
CO