Responses to exogenous pulsatile turkey growth hormone by growing 8-week-old female turkeys

A study was conducted in turkeys to determine the effects of pulsatile infusion of turkey growth hormone (tGH) on growth, feed conversion, carcass component parts, carcass composition, plasma metabolite concentrations, and other hormones associated with growth. Female turkeys, 8 weeks of age, were dually cannulated via the right jugular for intermittent (10 min every 2 hr) infusion of tGH at a low dosage (4.5 microgram tGH/infusion or 54 micrgoram/day), a high dosage (18 microgram tGH/infusion or 216 microgram/day) or vehicle infused controls (vehicle, 0.025 M NaHCO3, 0.025 M Na2CO3+5mg/ml NaCitrate, pH 9.4). Treatment was for 18 days. The second cannula was used to serially bleed the turkeys (5 or 10 min between samples) at 4 and 16 days of treatment to determine concentrations of GH, glucose, triacylglycerides (TG) non-esterified fatty acids (NEFA), and uric acid (UA). Overall GH was increased 74% above the control group in the low and 195% in the high treatment group. Baseline GH was increased 52% in the high group above the control group. The amplitude of GH peaks increased 292% in the low, and 574% in the high group above the amplitude of naturally occurring peaks in the control group. Infusion of tGH for 18 days did not affect overall daily gain, feed conversion, final body weight, tibiotarsus length, weights of pectoralis major, pectoralis minor, gastrocnemius or biceps femoris muscles, or weights of liver and offal. Abdominal fat pad weight (70% decrease), and percentages of carcass fat (4.9% decline) and carcass dry matter (2.3% decline) were lower in the high treatment group. Plasma TG and glucose were unaffected by treatment. Overall plasma NEFA concentration was increased in the high treatment group, and this increase was associated with an increase in the baseline concentration and incidence of pulses of NEFA, but not with the amplitude concentration of NEFA pulses. The dynamic nature of plasma NEFA concentration observed in this study suggests single time point measurements of this metabolite may not appropriately detect treatment effects. Plasma overall uric acid (UA) was decreased in the high treatment group in comparison to the control group, and this decrease was associated with a decrease in the baseline concentration of UA but not in the amplitude concentration nor incidence of UA pulses. Plasma insulin-like growth factor-I (IGF-I) concentrations were increased in the low treatment group at 4 but not at 16 days of treatment. Plasma triiodothyronine (T3) was increased in both the high and low treatment groups at 16 days of treatment, while tetraiodothyronine (T4) was depressed in the high treatment group in comparison to the control group. It was concluded that tGH infused in a pulsatile pattern in growing female turkeys does not affect body weight gain, feed conversion, or weight of muscles, but does affect carcass fat content and plasma concentrations of NEFA and UA, and concentrations of the growth hormone associated hormones, IGF-I, T3, and T4.