The abdominal fat tissue is very important in chickens due to its rapid growth as compared with other fat tissues. Most fatty acids are produced in the liver and stored as triglycerides in adipose tissues. Thus, the abdominal fat is a reliable parameter for estimating total body fat content as it directly correlates with the total lipid content in avian species. Nutritional factors play a key role in regulating body fat deposition. Therefore, this article discusses the effect of two such nutritional factors viz., protein and amino acids on the abdominal fat content and the mechanism of regulating abdominal fat deposition in poultry in a beneficial manner.
Protein is the most expensive component of poultry diets. The increase in the dietary protein content improves the daily weight gain, carcass yield, and meat quality by reducing body fat deposition and increasing protein content. A report shows that reducing dietary protein level during the starter, grower, and finisher phase, and compared with normal-protein diets as recommended by NRC, 1994 led to a significant increase in the abdominal fat content. An analogous study where increasing dietary protein level in the diets of broiler chickens in all three phases led to a significant reduction abdominal fat deposition compared with diets formulated according to NRC (1994) causing lean broiler chickens. Therefore, dietary protein content must play a direct or indirect role in the regulation of lipid metabolism. In 2002, it was found that reducing dietary protein content upregulates malic enzyme mRNA expression increases malic enzyme activity in the liver of broilers compared with the control, and vice versa. Further study also showed that increasing dietary protein content caused a significant reduction in hepatic enzyme mRNA expression in the livers of broiler chickens. Therefore, dietary protein level directly affects body fat deposition. Thus, it is important to suffice the protein requirements of birds to produce high-quality meat with low-fat deposition.
At present, only methionine, lysine, and arginine are known to beneficially regulate body fat deposition in poultry. Therefore, the addition of these amino acids in poultry diets should be ensured to prevent unnecessary fat deposition. Among these, methionine is the first limiting amino acid in poultry diet. It is essential amino acid as it directly affects on growth performance and helps in producing lean meat. A report shows that inclusion of L-methionine in poultry diet leads to a significant reduction in body fat content. The effect of dietary L-methionine in reducing the fat deposition may be associated with changes in lipolysis and lipogenesis. Lysine also has a prominent role in meat quality by increasing protein deposition, reducing the water-holding capacity, and enhancing muscle pH. The lysine supplementation in poultry diets significantly enhances lean meat production. A meat-type ducks fed with lysine-deficient diet gave significant high abdominal fat percentage while the inclusion of lysine eliminated this effect. Hence, addition of lysine in poultry diets promotes lean meat production by reducing carcass fatness via lipogenesis inhibition.
Another essential amino acid is the arginine which plays multiple roles in poultry production, implicated in reduction of carcass fat deposition. A study reports a significant reduction in the abdominal fat content in Japanese quails at 42 day of age 2.0% arginine supplementation at day zero of incubation. A corresponding study reported that providing 1.0% more arginine in addition to the NRC (1994) recommendations reduces the abdominal fat content by decreasing the activities of enzymes involved lipogenesis. In avian species, therefore, dietary L-arginine supplementation inhibits certain hepatic enzymes, which causes a reduction in the abdominal fat content by reducing the size of abdominal adipose cells.
Hence, the fat-reducing effects of protein and certain amino acids have not been fully clear. Thus this article makes an effort to elucidate our current understanding of the mechanism related to the effects of protein and amino acids that beneficially regulate abdominal fat deposition in poultry.