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Title: DIETARY PROTEIN AND TRIIODOTHYRONINE (T3) EFFECTS ON THE RESPONSE OF BROILERS TO ISOPROTERENOL AND CYCLIC ADENOSINE MONOPHOSPHATE IN VITRO

Author
item Rosebrough, Robert
item Mitchell, Alva

Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Excess fat production in the modern broiler accounts for an annual loss to the poultry industry of 800 to 950 million dollars annually. The original source of this problem relates to selection genetic practices that emphasized rapid growth at the expense of other carcass characteristics. The literature is of limited value in determining methods to depress fat synthesis and allow lean tissue synthesis to remain at an elevated rate. A strain of male chicks noted for its rapid growth was used to study the effects of dietary protein and triiodothyronine on the ability of chicks to synthesize fat. The line of chicks selected for rapid growth provided liver tissue that, when put into a culture system, exhibited a high rate of lipid synthetic ability. When lines of chickens were fed higher protein diets, they exhibited a decrease in the ability to produce fat. Likewise, including the hormone triiodothyronine in the diets also decreased fat synthesis. These regimens may be of value if the slight growth-depressing effect of triiodothyronine can be overcome.

Technical Abstract: Seven-day-old Indian River male broiler chickens were fed diets containing 120, 210 or 300 g crude protein + 0 or 1 mg/kg triiodothyronine, T3, (Exp 1) and 120, 150, 180 or 210 g crude protein + 0 or 1 mg T3 (Exp 2) to determine the effects of crude protein levels and T3 on growth and metabolism Body composition of chickens was determined by a combination of dissection of muscle, abdominal fat pads and chemical extraction (Exp 1). In vitro lipogenesis (IVL) was determined in both experiments by incubating liver explants for 2 h at 37 C in the presence of 10-4 M dibutyrl cyclic adenosine monophosphate (cAMP) or 10-5 M isoproterenol (ISO) and 10-2 M-[2-14C]acetate. Acetate incorporation into total lipid was an indication of IVL. Activity ratios for each of these additions relative to controls (-cAMP -ISO) were calculated to ascertain basal vs inhibited rates of IVL. The relative muscle mass was increased by increasing crude protein from 120 to 210 g /kg diet but not from 210 to 300 g/kg diet. Dietary T3 decreased total body lipid regardless of the dietary crude protein level. Increasing dietary crude protein decreased (P<0.05) basal IVL (-cAMP -ISO) but not IVL (+cAMP). Dietary T3 decreased basal IVL in birds fed the diet containing 120 and 210 g crude protein/kg diet but had little effect on the two inhibited states of lipogenesis (+cAMP or +ISO). The component of lipogenesis sensitive to in vitro inhibition is also the component under dietary control.