Lysine and other amino acids for feed: production and contribution to protein utilization in animal feeding - Yasuhiko Toride

Yasuhiko Toride
Ajinomoto Co., Inc.
Japan

INTRODUCTION

The industrial application of amino acids for feed has an almost 40-year history. In the late 1950s and 1960s, DL-Methionine, produced by chemical synthesis, began finding its way into poultry feed. Production of L-Lysine by fermentation was started in Japan during the 1960s.

In addition to DL-Methionine and L-Lysine, HCl, L-Threonine and L-Tryptophan were introduced in the late 1980s. With progress in biotechnology, the cost of production of each amino acid has been significantly reduced, which has been one of the key factors in the expansion of use of amino acids in animal feed.

Amino acids for feed now play very important roles in improving the efficiency of protein utilization in animal feeding.

PRODUCTION OF AMINO ACIDS FOR FEED

The estimated production of amino acids for feed is summarized in Table 1.

DL-Methionine is produced by chemical synthesis from raw materials such as acrolein, hydrocyanic acid and methyl mercaptan. The above-estimated production includes that of methionine hydroxy analog, which has nutritional value equivalent to that of DL-Methionine.

TABLE 1
Estimated production of feed-grade amino acids in 2000

Three other amino acids, L-Lysine HCl, L-Threonine, and L-Tryptophan, are produced by the fermentation method. By cultivating a special microbial strain developed for the production of each amino acid, in a medium containing glucose or sugar and other nutrients (ammonium sulphate, etc., as nitrogen sources, minerals and vitamins), an amino acid can be efficiently produced. The amino acid is extracted from the fermentation broth with ion exchange resin treatment, etc. The fermentation yield of the strain is a key factor in the productivity of amino acids, which has been steadily improved with the introduction of new biotechnology. For example, the fermentation yield of L-Lysine HCl from glucose or sugar has now exceeded 50 percent.

APPLICATION OF AMINO ACIDS FOR FEED

The requirements of amino acids in animals are well defined in various sets of recommendations such as those of NRC (National Research Council), USA, etc. Requirements vary depending on the species and age of animals. Amino acids should be supplied either in the form of protein or crystalline amino acids in feed to meet requirements. By comparing requirements and the actual amino acids present in feed, the order of ‘limiting amino acids’ can be estimated. The orders of limiting amino acids in pig and broiler feeds, composed of corn (or wheat) and soybean meal, are summarized in Table 2.

TABLE 2
Order of limiting amino acids

Crystalline amino acids should be added to feed in the order of limiting amino acids when the protein content of the feed is reduced, which is the reason why DL-Methionine and L-Lysine HCl were initially introduced to feed. Now, with a more economic supply of L-Threonine and L-Tryptophan available, use of amino acids has entered a new era, in which the use of second and third limiting amino acids is taking off. For example, in the past two to three years, the annual growth rate of L-Threonine usage has been above 20 percent. Since the protein level required by livestock is reduced further with the introduction of second and third limiting amino acids, use of the first limiting amino acid will also be expanded.

CONTRIBUTION IN PROTEIN SUPPLY

The animal industry can be defined as an industry producing proteins of higher value (meat, milk) from less expensive protein sources (vegetable proteins such as soybean meal). To meet the growing demand for protein worldwide, it is essential to improve the efficiency of conversion of proteins from feed to meat. Amino acids for feed now play indispensable roles in improving the efficiency of animal protein production, and contribute to increasing protein supply. For example, the contribution of L-Lysine HCl to protein supply can be estimated as follows. A simple equation illustrates substitution of the protein source (soybean meal) with corn (maize) and L-Lysine HCl:

50 kg/tonne of soybean meal = 48.5 kg/tonne of corn + 1.5 kg/tonne of L-Lysine HCl

The substitution corresponds to a 2 percent reduction of the protein level in feed. This equation means that 1 tonne of L-Lysine HCl can save the usage of 33 tonnes of soybean meal. The estimated usage of L-Lysine HCl in the world, 550 000 tonnes/year, corresponds to the saving of 18 million tonnes of soybean meal, which is equivalent to almost half of the soybean meal production in the United States (38 million tonnes in 2000). How to utilize limited arable land efficiently to maximize the supply of food should also be considered. The above equation can be interpreted in the following way to show how L-Lysine HCl can improve the efficiency of utilization of cultivated areas. The following yields are assumed for the estimation in Table 3. Soybean - soybean meal 80 percent corn - cornstarch 60 percent cornstarch - L-Lysine HCl 50 percent. These values indicate that the arable land required for the production of 48.5 tonnes of corn, plus 1.5 tonnes of L-Lysine HCl is only about one quarter of that required for 50 tonnes of soybean meal. The introduction of second and third limiting amino acids can further reduce the usage of precious protein sources and arable land required for their production. For growing pigs, the reduction in usage of soybean meal will be about 100 kg/tonne of feed, in a feed formulation with L-Lysine HCl, L-Threonine and L-Tryptophan. This is double the saving compared with a feed formulation having L-Lysine HCl only.

TABLE 3
Comparison of arable land required for soybean meal, corn and L-Lysine HCl

CONTRIBUTION TO PROTECTING THE ENVIRONMENT

Nitrogen excretion due to animal farming is posing a serious threat to human health through ammonia or nitrate/nitrite pollution in soil and water. Farmers now must therefore face more and more stringent environmental regulations. Decreasing excessive protein in feed by supplementation of amino acids is the most cost-effective way to solve the problems of nitrogen pollution associated with animal feeding. It is a preventive measure aimed at reduction of pollutant output at its source. A literature review was conducted to quantify the impact of low-protein diets on nitrogen excretion. On average, reduction of crude protein content in a diet by one percentage point can yield about an eight to ten percent reduction in nitrogen excretion. Reducing the crude protein level by three to four percent, with supplementation of first, second and third limiting amino acids, will yield at least the same growth performance but with around 20-30 percent reduction in nitrogen excretion.

COMPARISON WITH HIGH-LYSINE CORN

It is expected that the introduction of High-Lysine Corn will make the same contribution as L-Lysine HCl to the protein supply and to reducing nitrogen pollution. High-Lysine Corn with about 50 percent higher lysine content than conventional corn (0.40 vs. 0.26 percent) was developed with the introduction of new plant biotechnology. The combination of High-Lysine Corn and soybean meal will attain the optimum lysine content in feed without L-Lysine HCl supplementation. However, the feasibility of large-scale commercial production of High-Lysine Corn is still questionable. With the expected identity preservation (IP) handling cost, it is said that at least US$14/tonne (35 percents/bushel) of benefit is necessary to make value-added crops commercially feasible. In the case of High-Lysine Corn, the benefit comes from an increase of 0.14 percent lysine content or 1.4 kg lysine/tonne of corn, which corresponds to 1.75 kg of L-Lysine HCl. At the current L-Lysine HCl price of around $1.5/kg, the benefit can be calculated to be only $2.6, which is far below the anticipated benefit of $14/tonne. L-Lysine HCl is thus still a much more economical source of lysine than High-Lysine Corn.

FUTURE PROSPECTS OF AMINO ACIDS FOR FEED

Improving the efficiency of protein utilization in animal feeding with the application of amino acids for feed, will become more and more important in securing the protein supply and protecting the environment. In addition to the four kinds of amino acids noted above, the next limiting amino acids, Isoleucine, Valine and Arginine, will be introduced in the near future. For ruminants, so-called by-pass amino acids, which can escape microbial degradation in the rumen, have recently been introduced. Consumers’ concern regarding bovine spongiform encephalopathy (BSE) has been forcing dairy farmers to limit the usage of animal protein such as blood meal in feed, which will further accelerate the usage of amino acids in ruminant feed.