We all know amino acids are building blocks of life. The application of amino acids in feed industry has been since four decades. Amino acids for feed now play key role in improving the efficiency of protein utilization in animal feeding. Among others, let’s discuss DL-Methionine since it’s the first limiting amino acid, followed by L-Lysine and L-Threonine.
Methionine is an essential amino acid required by poultry in sufficient amount for optimum body weight gain or egg production. Deficiency of methionine therefore causes retarded growth in broilers and reduced egg production in layers. On the other hand, surplus of methionine has been associated with atherosclerosis. Methionine is also a major constituent in feather formation. Its deficiency leads to poor feather growth and rise in the feather pecking in order to obtain adequate methionine. This behaviour can lead to cannibalism among the flocks. This could be the worst nightmare ever possible to farmers. To our rescue, synthetic DL-Methionine began finding its way into poultry industry since late 1950s. Till now broiler requirements are been met by the use of synthetic methionine since it’s affordable to the farmers. By now we can sense that how adverse effect can DL-methionine have on chickens.
The question that comes to our mind is- How safe is synthetic Methionine to poultry?
To answer this, we first need to know little background chemistry about DL-Methionine. DL-methionine contains two isomers L-form and its mirror image D-form in equal ratios. However, only L-methionine can be utilized to synthesizer protein. The second half D-methionine first needs to be converted to L form and then it’s available to use. To our surprise, D-methionine is not converted completely but around 90% in chickens. So what happens to the rest of the 10%? So if you learnt what happens in calves, it seems that it may result in elevated plasma methionine, then it could be evident that traces of DL-methionine can be found in the carcasses of Methionine fed broilers. (J. P. Felix D’Mello, Amino acids in animal nutrition, CABI publishing, UK).
Poultry methionine requirements have always been into controversies. It has been heavily criticized for the use of synthetic amino acid in the feed to increase the bird growth rather than its health. Moreover, synthetic methionine disturbs the whole system of nitrogen cycle in the poultry. This has led to the prohibition on the use of synthetic methionine in animal feed formulation by United States Department of Agriculture (USDA), 2000.
But not forgetting that a well balanced dietary protein and amino acids for poultry is a high priority issue among nutritionists for various reasons. First, cost of proteins and individual amino acids can be expensive nutrients in feed per unit weight. The price fluctuation of DL-Methionine and supply chain discrepancies result is massive shift of feed prices and reduces your profit. Therefore, selecting the appropriate level of amino acids becomes your critical economic decision. You will reach this goal only if you are dosing your methionine correctly. Inconsistency can never be avoided in an industry where raw materials are heavily applied. Therefore whatever you add in your feed diet, will surely affect your main objective. Therefore, addition of supplemental methionine in feed formulation requires precision. Second, the environmental pollution issues about nitrogen excretion from the poultry farming which can cause pollution of soil, air and water. A study shows that one percent reduction of crude protein in a diet can yield 8 to 10% reduction of nitrogen excretion. Hence it can be said that 3 to 4% reduction of crude protein with supplementation of first, second and third limiting amino acids can yield same growth performance with 30 to 40% reduction of nitrogen emission. And third, poor quality dietary proteins and amino acids can have major negative impact in heat stress conditions which is because of inefficient amino acid digestibility.
Well, many of the scientists are in constant discovery or invention to combat these hurdles. Moritz along with its colleagues in its article explains the use of feed restriction to increase commercial broiler forage intake. Thus, the plant material consumed along with any insects if available can be sufficient to obtain methionine. To read more see (Moritz, J. S., A. S. Parsons, N. P. Buchanan, N. J. Baker, J. Jaczynski, O. J. Gekara and W. B. Bryan. 2005. Synthetic methionine and feed restriction effects on performance and meat quality of organically reared broiler chickens. Journal of Applied Poultry Research 14:521–535). However, the availability of the methionine solely depends on the forage composition and its management. Also providing large scale flocks with quality pasture would be difficult. In addition, the forage quality and quantity will differ significantly time to time.
Halder and Roy have compared the performance of broilers between no added methionine group, synthetic methionine fed group and herbal derived methionine group (Halder, G. and B. Roy, 2007. Effect of herbal or synthetic methionine on performance, cost benefit ratio, meat and feather quality of broiler chicken. Int. J. Agric. Res., 2: 987-996). The results show that liver triglycerides in methionine fed group were evidently high in contrast to herbal derived methionine group. Overall performance in both methionine-supplemented groups was found similar (higher than the methionine deficient group). However, the quality of the protein makes it difficult in digestibility in the intestine.
To summarise, there is still no proper way out to this crisis. Remember, Science is never done, it’s always changing. The goal of science is to devise framework, to describe how things works together, to study things are right now so that we can predict how things will be in the future. And so if we learn to trust science in all its fuzziness and incompleteness, it can prove to be best tool to find solution to these problems. After all, animal welfare, managing food safety and environmental issues are our major concerns.