Answer: The protein and amino acid concentrations presented as a requirement by the NRC are to support maximum growth and production in fast-growing meat birds. Achieving maximum growth and production may not always ensure maximum economic returns, particularly when prices of protein sources are high (NRC, 1994). And maximum economic returns may not be the only goal. For some producers, product quality (flavor and nutrition) may be as significant as quantity produced. According to Sundrum (2005), there are no effects on animal health from feeding a suboptimal diet or low-nutrient diet, but the birds may not be fully realizing their genetic potential. In fact, breeding companies that sell specialty birds usually show expected growth performance on a high-nutrient diet as well as a low-nutrient diet designed for conventional and specialty production, respectively.
Low-nutrient diets or feed restrictions are often used in the starter phase to slow the growth of fast-growing birds in order to reduce metabolic disorders and lameness. Feed restrictions have also been implemented to reduce feed spillage and better document feed efficiency. Feed density can be increased later for compensatory gain (Sundrum, 2005). A bird’s ability to adapt to variations in feed supply still exists (Sundrum, 2005). However, fast-growing, high-yielding animals are more sensitive to suboptimal feed rations than slower-growing or low-yielding animals. Stress levels may increase due to sudden changes in a feed ration, leading to depressed levels of growth. U.S. organic poultry companies are concerned that fast-growing birds with reduced MET levels in their diet will not only perform poorly, but will also suffer impaired immune function, resulting in poor feathering, feather pecking, cannibalism, and mortality. The antioxidant mechanisms of sulfur amino acids and their compounds are important. Normally, cells are equipped with antioxidant mechanisms to deal with free radicals. If antioxidants are out of balance, problems can occur that cause decreased animal performance. Sulfur-containing compounds such as MET and CYS are powerful antioxidants that can prevent damage in cells (Anon, 2009). Elwinger and Tausen (2009) found that reduced MET levels reduce feather cover and egg weight, although the production of eggs was not affected. They also found that feed intake increased as feather cover deteriorated, thus reducing feed efficiency.
Ambrosen and Petersen (1997) studied the impact of protein levels in feed (11% vs. 19% crude protein) on cannibalism and plumage quality. The plumage improved with increased protein. Chickens supplemented with MET had better plumage quality and reduced feather pecking compared to the MET-deficient birds. However, Biedermann et al. (1993) did not show poor feathering with low protein levels. There are many factors involved in feather pecking beside the nutrient level, such as stress derived from living conditions. Feather pecking may occur even on farms with high levels of MET in the diet, for unrelated reasons.
To learn more, consult the ATTRA publication Organic Poultry Production: Providing Adequate Methionine, which discusses organic husbandry including living conditions, health, genetics and origin, feed and processing as specified under the livestock requirements of the U.S. Department of Agriculture National Organic Program.
Ambrosen, T. and V.E. Petersen. 1997. The influence of protein level in the diets on cannibalism and quality of plumage of layers. Poultry Science. Vol. 76, No. 4. p. 559-563.
Biedermann, G. von, N. Schmiemann, and K. Lange. 1993. Investigations of the effects of plumage condition at different ages in laying hens. Archiv fur Gefl ugelkunde. Vol. 57, No. 6. p. 280-285.
Elwinger, K. and R. Tausen. 2009. Low-methionine diets are a potential health risk in organic egg production. European Symposium on Poultry Nutrition, Edinburgh, Scotland, August 23-27, 2009.
Sundrum, A. 2005. Possibilities and limitation of protein supply in organic poultry and pig production. Organic Revision: Research to support revision of the EU regulation on organic agriculture.
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