Concentrations of hormones, glucose, triglycerides and free fatty acids in the plasma of broiler chickens selected for weight gain or food conversion

Abstract

1. The concentrations of growth hormone (GH), insulin-like growth factor I (IGF-I), thyroxine (T4), triiodothyronine (T3), reverse-triiodothyronine (rT3), triglycerides (Tri), free fatty acids (FFA) and glucose (Glu) were determined at 2, 4 and 6 weeks of age in blood plasma of male and female chickens of broiler lines selected for body weight (GL) or food conversion (FC). 2. Plasma concentrations measured in the same animal over a 24 h or a 2 week interval were not significantly correlated with each other. For different traits measured in the same plasma sample only the correlation between T4 and rT3 differed significantly from zero. 3. All traits were dependent on age. Line and sex effects were significant (P less than 0.05) for GH, T4, Tri, FFA and Glu. Additionally, line significantly influenced the plasma T3/T4 ratio and sex influenced plasma rT3. Interactions between line, sex and/or age were seldom significant. 4. Within line and sex, GH (at 6 weeks of age) and T3 (at 4 weeks of age) were negatively, and IGF-I and Tri (both at 6 weeks of age) positively correlated with the amount of abdominal fat at 6 weeks of age. No significant correlation between body weight at 2, 4 or 6 weeks of age and any of the plasma traits was found.

Ontogeny of growth hormone receptor gene expression in tissue of growth-selected strains of broiler chickens

“…Selection for higher BW results in lower plasma GH levels (S20 and S21) and higher hepatic and plasma GH-binding activity in liver membrane and plasma which is consistent with other studies (Burke & Marks 1982, Goddard et al 1988, Leenstra et al 1991, Vanderpooten et al 1993. The slowest growing strain (S90) appears to be hyperpituitary since these birds have higher plasma GH, IGF-I, and T 3 AUCs than the parent unselected 1970's strain (S20).…”

“…Fast-growing lines of broiler chickens have lower circulating GH levels than slow-growing lines (Scanes et al 1980, Burke & Marks 1982, Goddard et al 1988, Leenstra et al 1991. Plasma GH concentrations are higher in chickens selected for food conversion (slow-growing) than in chickens selected for body weight (BW) (fast-growing) (Decuypere et al 1991). However, no consistent difference was found in plasma GH concentrations among other lines selected for weight gain, food consumption, or efficiency of food conversion (Tomas et al 1991).…”

“…Selection for increased growth rate in S80 (from S90) and in S21 (from S20) does not affect plasma IGF-I levels. Numerous studies have shown that genetic selection of broiler chickens for improved growth traits does not affect plasma IGF-I levels (Cahaner 1988, Goddard et al 1988, Leclercq 1988, Sorensen 1988, Whitehead 1988, Leenstra et al 1991, Tomas et al 1991. However, plasma IGF-I levels were significantly lower in two fast-growing strains than in a slow-growing strain (Lee et al 1989).…”

“…There was no significant difference in plasma GH levels in chickens divergently selected for either low or a high abdominal fat content although hepatic GH-binding activity was higher in the fat line than in the lean line (Buyse et al 1994). Hepatic GHbinding activity is also higher in fast-growing chickens than in slow-growing chickens (Decuypere et al 1991). Higher plasma GH concentrations in chickens selected for feed efficiency causes down-regulation of hepatic GH-binding activity (Vanderpooten et al 1993).…”

“…Generally, selection for rapid growth alone results in fatter chickens, while selection for improved feed efficiency as well results in leaner, albeit slightly slower-growing chickens. Fast-growing lines of broiler chickens have lower circulating GH levels than slow-growing lines (Scanes et al 1980, Burke & Marks 1982, Goddard et al 1988, Leenstra et al 1991. Plasma GH concentrations are higher in chickens selected for food conversion (slow-growing) than in chickens selected for body weight (BW) (fast-growing) (Decuypere et al 1991).…”