Temporal fluctuations of plasma LH and testosterone in Charolais bull calves during the first year of life

Abstract

Plasma LH and testosterone have been measured by radioimmunoassay in samples collected weekly from 10 Charolais male calves from birth till 1 yr of age. Plasma LH increased from the 1st to the 5th wk of age, then fluctuated widely from the 5th to the 20th wk (3-5 ng/ml) and finally decreased to about 2 ng/ml and remained steady up to 1 yr of age. Plasma testosterone increased very slowly from the 1st to the 20th wk of age and then increased more rapidly with large fluctuations up to 1 yr. Thus an intense LH release between the 1st and the 5th mth of life was not followed by a clear testosterone release suggesting that testicular sensitivity to LH was not yet established. Conversely, after the 6th mth of age discrete LH variations were able to induce large releases of testosterone into the blood. It is suggested that high pituitary activity during the first month of life is a signal for puberty.