The Functions Of Methionine In Poultries
With the continuous development of biochemical technologies in animal husbandry and human nutrition, there have been many changes in the interests of amino acids. Here, the difference in efficiency between the physiological function of methionine and sources was examined.
In the past, the function of amino acids as constituents of proteins has been studied for a long time. However, as biochemical technologies develop in many fields such as cell culture, the physiological functions of amino acids have been achieved and must be considered when designing feed formulations to maximize animal growth.
Since methionine is limited to vegetable protein sources and requires high levels of methionine in feather growth and protein synthesis, methionine is always classified as the first limiting amino acid in poultry.
Use of methionine in poultry diets
Since methionine is limited to vegetable protein sources and requires high levels of methionine in feather growth and protein synthesis, methionine is always classified as the first limiting amino acid in poultry. Methionine has many physiological functions, such as an important methyl donor as a methyl group (CH4) necessary for the metabolism of the human body. Methionine is known to reduce oxidative stress in vivo by increasing antioxidant compounds such as glutathione.
Methionine additives for poultry and other feeds are the methionine hydroxy analogue L-methionine, DL-methionine or MHA-FA. All plants and animals can only use the L-isomer methionine, and only L-type methionine existed in the protein. The D-isomer of methionine and MHA can also be used, but it must be converted to the L-form by in vivo enzymatic reactions (Figure 1). However, it can be questioned whether the lysed amino group can return the methionine chemical skeleton with 100% efficiency. In addition, the two enzymatic reactions during the conversion of isomers require energy. Therefore, when DL methionine or MHA is used instead of L-methionine, the relative bioavailability (RBA) naturally decreases due to the unnecessary energy consumption of enzyme conversion.
Figure 1 – The converting process from D-methionine to L-methionine.
Conversion of D-methionine to L-methionine
The DAAO enzyme necessary for D-methionine conversion is abundant in the liver and kidneys of chickens. However, according to D'Aniello (1993), young animals have lower levels of these enzymes. As the animal grows, the activity of the enzyme will increase, but it will take quite a long time to activate a sufficient level in the body, as shown in FIG. 2 .
As we all know, the growth performance of broilers in the first week has a huge impact on overall performance. The chicks had a birth weight of only 40 grams and had to gain 4.5 times (180 grams) after 1 week to maintain the target weight on the scheduled sales day. If the weight of the chicken is reduced by 10 grams within 7 days, the final market weight can be reduced by 60-70 grams on the 35th day of delivery. Therefore, careful consideration is given to using D-methionine which has not been sufficiently utilized in chicks to maximize the growth of the fermentation stage.
Effect of Methionine on Intestine
Glutathione plays an important role in antioxidant defence. It is capable of preventing damage to intestinal cellular components caused by reactive oxygen species such as free radicals, peroxides and heavy metals. Especially, increased glutathione concentration affects the development of small intestinal villus.
Shen et al. (2014, 2015) have shown that feeding L-methionine increase villi development in both broilers and swine as compared to feeding DL-methionine in young animals (Figure 3). Analysis of villous tissues of both L or DL treatments showed that significantly higher glutathione levels were observed in the L-methionine supplementation group. Additionally, both the height and width of the villi were improved in the L-methionine supplementation group.
Differences of glutathione synthesis and RBA between L-methionine and DL-methionine (Shen et al., 2015).
The importance of methionine
In commercial poultry diets, methionine is usually the first limiting amino acid. Methionine not only serves as an integral part of the body's protein, but also participates in the development and growth performance of the digestive tract. In addition, it has the function of increasing muscle mass, feather development and increasing egg production in poultry.
The importance of the physiological function of methionine must be emphasized. L-methionine is the only biologically active form of methionine that is readily available for young chick intestinal cells.