Practical use of synthetic amino acids in poultry diets
Feed supplement
The primary use of synthetic amino acids in poultry production is as a feed supplement. For optimum health and performance, the poultry diet muse contain adequate quantities of all nutrients needed, including amino acids. The essential amino acid furthest below the level needed to build protein is known as the limiting amino acid. A shortage of the limiting amino acid will constrain bird growth, reduce feed efficiency, and in extreme cases cause a nutritional deficiency. Supplementation with synthetic amino acids increase feed conversion efficiency, thus lowering feed costs per unit of weight gain or production (Pond, Church and Pond, 1995). Methionine is often the first or second limiting amino acid in most diets, and so is most representative of amino acids fed as a nutritional supplement (Buttery and D’Mello, 1994).
Adding synthetic essential amino acids to the diet allows a reduction in the dietary crude protein content while concomitantly meeting the requirements for all essential amino acids. Liu et al (2005) reported that beneficial effect of added synthetic lysine was obtained for feed consumption, egg production, egg mass, and egg with at 13 percent protein level, and for feed conversion at 14.3 percent protein level, indication that the quality of low-protein diets can be improved by added lysine when the Met+Cys/Lys ration is maintained at 0.75. He also found that added synthetic lysine had no influence on egg quality.
Lehmann et al. (1996) reported a marked increase in breast meat deposition in response to dietary lysine in turkey. Increasing dietary lysine decreased intramuscular fat content and increased the protein levels in breast meat.
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Better Utilization
The physiological basis of utilization of free amino acids in generally more favorable for poultry than for pigs. Firstly, poultry are usually fed a more concentrated ration ad libitum. Although there may be some variation in the feed intake from morning to afternoon, it is generally believed that the diumal variation of nutrients in plasma is lower in poultry than in pigs (Riis, 1983). This forms the basis of a better utilization of synthetic amino acids in protein synthesis. Secondly, poultry are more sensitive to amino acid imbalance, which has been shown to have an adverse effect on the feed intake. Experiments with chicken have supported the hypothesis that diets formulated to minimize excess of amino acid over the chick’s known requirement would improve the efficiency of protein and energy utilization (Waldroup et al., 1976). Moreover, in some instances the relative proportion of essential amino acids may be of greater significance than the absolute amounts because of complex relationship between amino acids (Brewer et at., 1978). Therefore, the advances in balancing amino acid composition of diet and physiological basis for a high utilization of added free synthetic amino acids are generally more favorable in poultry than in pigs. This interpretation was confirmed in a recent study with chicken by Sibbald and Wolynetz (1985). The utilization of synthetic lysine was 0.92, which was significantly (p<0.05) higher than that of protein-bound lysine (0.88).
Nutritionists currently use synthetic source of methionine and lysine and in certain situation threonine and tryptophan may be considered as dietary ingredients. Such synthetic amino acids are assumed to be utilized 100 percent since there is no loss due to ineffective digestion. The same amino acids in intact proteins, such as soybeans meal, may be only 90 percent digestive and so free amino acids seem to have distinct advantage as ingredients. However, not all protein within intact protein needs to be released as such during digestion, because thee is some absorption of pepitides. Boorman and Ellis (1996) suggested that one advantage of a bird utilizing peptides is that there will be less bacterial degradation within the digesta and that this activity should not be under estimated.
Sudden influx of feed are not normal in poultry, and in broiler breeder pullets that are severely restricted in feed, use o synthetic amino acids as a proportion of total amino acids is quite small. Apart from the suggestion about interference by bacterial degradation, it is assumed that synthetic amino acids are utilized as efficiently as are those indigestible intact protein, in most practical feeding situations.
If the diet contains a preponderance of synthetic amino acids, there could be a limitation on supply of non-essential nitrogen, either as intact protein or free amino acids. In a normal diet the supply of non-essential amino acids. When more synthetic amino acids are used, not only is crude protein supply reduced but also excess of limiting amino acids is usually minimized. Limiting supply of non-essential nitrogen is the other quoted cause of poor performance of birds fed low protein amino acid fortified diets, although this concept has never been adequately quantitated. There are about equal number of well conducted studies by eminent researchers showing normal or sub optimal growth, when protein content of the diet is reduced. Such differential results may occur from over estimation of amino acid supply in intact proteins, failure to maintain supply of some other nutrients that influence amino acid utilization, strain differences in amino acid needs or failure of growth per se to fully quantitative the complex reaction of birds to amino acid supply. For young broiler chicken at least, caution is necessary when using diets with crude protein equivalents of much less that 16-17 percent assuming optimum growth rate is desired. Likewise, the growth rate of birds is often interior when regardless of amino acid balance; the ratio of crude protein synthetic acids is much less than 16:1.
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