Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/1998
Publication Date: N/A
Citation: 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 to remain at an elevated rate. A strain 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: Indian River male broiler chickens growing from 7 to 28 d of age were fed diets containing either 120 or 210 g crude protein and 0 or 1 mg triiodothyronine (T3)/kg of diet to study in vitro lipogenesis (IVL). In addition, a carry over period (180 g crude protein/kg diet from 28 to 40 d of age) was used to test the persistence of prior treatment effects. The higher protein level increased, but T3 decreased (P<0.01) growth and feed consumption at 28 d of age. The lower protein level increased (P<0.05) and T3 decreased IVL in 28-d old chickens. The higher protein level increased plasma IGF-I during the period from 7 to 28 d; however, this effect lasted for only 6 d following the switch to a common diet. Plasma growth hormone (GH) at 28 d of age was inversely related to dietary protein level. For the most part, changes in metabolism may be specific to the particular dosing interval and are only sustained for a short period of time following the feeding of a common diet.