Pituitary and Plasma Growth Hormone Levels in Bulls from Birth to One Year of Age

Abstract

Sixty-five Holstein bulls were killed in groups of five at monthly intervals from birth to 12 months of age to investigate relationships between body growth and pituitary or plasma growth hormone (GH). The correlation coefficient between pituitary GH concentrations measured by radioimmunoassay and by rat tibia test bioassay was 0.60. Body weight increased linearly with age, but pituitary GH concentration and content showed a peak at 3 to 4 months and plasma GH concentration was relatively constant after falling from high levels at birth. None of the measures of GH status was closely related to age or to measures of growth.