Relationship of Plasma Growth Hormone to Growth Within and Between Turkey Lines Selected for Differential Growth Rates

Abstract

The ontogeny of plasma growth hormone (GH) was determined within and between genetically-related turkey lines selected for differential growth rates. Blood samples were obtained at weekly intervals from hatching through 195 days of age from male and female poults of a slow-growing, randombred line (RBC-2), representing the base population, and a fast-growing line selected over 20 generations from RBC-2 for increased 16-wk body weight (F).Growth rate of the F line exceeded that of RBC-2 during the very early (0 to 14 day) posthatch period (P<.05), but was not different from that of the RBC-2 line by 77 to 195 days of age. Males of both lines were larger than females at all ages (P<.05).Plasma GH increased from hatching until 2 wk of age and declined thereafter in both lines. Differences between overall plasma GH concentrations of the lines were not observed during the 0 to 14 day period, but concentrations were higher (P<05) in RBC-2 than F birds thereafter (21 to 195 days of age). Plasma GH concentrations initially (0 to 14 days) were higher in females than in males for both lines (P<.05), but thereafter (21 to 195 days) declined more rapidly and averaged lower overall in females than in males (P<.05).Correlations between measures of GH and growth rate within lines over age were strongly positive (r = .83 to .93; P<.001). The strong relationship of plasma GH to growth within lines is supportive of a role for GH in postembryonic growth in poultry. However, relatively lower GH concentrations in the faster-growing F line than the slower-growing RBC-2 line indicates that factors other than apparent plasma concentrations of the hormone are involved.