Pulsatile patterns of plasma growth hormone in Turkeys: Effects of growth rate, age, and sex

Male and female turkeys of a slow-growing, random bred line (RBC-2) and a fast-growing line (F), selected over 21 generations from RBC-2 for increased 16-week body weight, were intravenously cannulated and serially sampled at 10-min intervals for 6, 8, 9, 10, or 12 hr at 2, 4, 8, 14, and 24 weeks of age, respectively, for determination of the pulsatile pattern of plasma growth hormone (GH) concentration. Overall mean plasma GH concentration was greater for RBC-2 than F beginning at 4 weeks of age, when body weights of the two lines had diverged. Males exhibited both greater body weight and greater overall mean GH than females beginning at 4 weeks of age. Overall mean GH concentration, peak frequency and amplitude, and baseline concentrations declined with age for both lines. The RBC-2 line exhibited greater peak frequency, peak amplitude, and baseline mean concentration than the F line at 4, 8, and 14 weeks of age. Males exhibited greater peak frequency, peak amplitude, and baseline concentration than females at 4, 8, and 14 weeks of age. Peak duration was the most consistent profile parameter across lines, ages, and sexes, and averaged 68 min overall. Estimated GH pool size was consistently greater in males than females at all ages, and was greater in the F than RBC-2 line at 2 weeks of age when relative gain was maximal for both lines. Pool size was the GH parameter most highly correlated with body weight across treatment groups.