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HMTBa (2-hydroxy 4-methyl-thio-butanoic acid) is an organic acid and the functional analog of the essential amino acid methionine. When consumed by animals, DL-HMTBa is converted into methionine in the liver and other tissues for protein synthesis. First developed by Monsanto in 1954 (Insert Reference), HMTBa is manufactured by several corporations as a feed grade methionine additive. HMTBa functions as a supplement to the diets of many species of farm-raised animals and helps ensure efficient grow (Insert References).

Function
Used to supplement to animal diets, HMTBa can provide the incrementally required methionine in an animal’s diet to efficiently synthesize protein into muscle tissue. Animals do not naturally generate methionine; therefore, it must be consumed through dietary intake. Methionine is recognized as one of the most important amino acids to supplement in poultry diets, and it is second only to lysine in pig diets.

Heat Stress
HMTBa can be absorbed throughout an animal’s body through a process known as diffusion rather than active transport which is required for DL-methioine. Differences in absorption are particularly important during heat stress. There are three absorptive pathways in the digestive tract: diffusion, carrier-mediated transport and active transport.

Organic Acid
Being an organic acid, methionine precursor, HMTBa fed in excess of requirement does not result in decreased intake, growth, or poorer feed efficiency that can be observed when excess methionine is fed from ingredients or DL-methionine. HMTBa is an organic acid and thus has an acidifying affect compared to a buffering effect by DL-methionine.

Antioxidant
HMTBa, as a precursor of methionine, is also a precursor to various antioxidants including taurine and glutathione (Figure 16, Shoveller et al., 2005). DL-methionine can also lead to a production of these two antioxidants since it is also a precursor of methionine. However, in a heat stress model, HMTBa has been shown to be more effectively converted to taurine and glutathione than DL-methionine (Figure 17 (Willemsen, et al., 2011; Martín-Venegas, et al., 2006).

Liquid
HMTBa is primarily available in a liquid form that is 88% active ingredient and 12% water. Liquid HMTBa is currently manufactured by Novus International, Adisseo, and Sumitomo. Liquid HMTBa is stored in tanks of various sizes at feed mills where it is sprayed into large mixers.

Dry
Dry HMTBa is created by reacting the liquid form with a calcium carrier. The result is a product with 84% active ingredient and 16% calcium salt. Because not all feed mills are equipped to handle liquid, dry provides an option to add HMTBa directly to feed mixers without the need to spray liquid.