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LETTERS TO THE EDITOR |
Novus International Inc., St. Charles, MO 63304
2 Corresponding author: Jim.Richards{at}novusint.com
We would like to thank D. Hoehler for his comments ("A Misleading Approach to Determine the Methionine Activity of Organic Trace Minerals"), giving us the opportunity to clear up several misconceptions that he and possibly others may have regarding the chemical structure and biological activity of Mintrex organic trace minerals. First, Mintrex organic trace minerals are not the calcium salts of DL-2-hydroxy-4-(methylthio)butanoic acid (DL-HMTBA), as he describes. Rather, Fourier transform infrared spectroassay and crystal structure analyses have demonstrated that Mintrex molecules are atoms of Zn, Cu, or Mn, each chelated by 2 molecules of DL-HMTBA. The calcium salt of DL-HMTBA is another molecule entirely. Although the calcium salt is fed to provide Met activity, the main purpose of feeding Mintrex is to provide a highly bioavailable source of trace minerals. Nevertheless, the DL-HMTBA ligands in Mintrex would be expected to provide substantial Met activity, which is clearly demonstrated in our paper (Yi et al. 2007).
Second, the notion that DL-HMTBA is inferior as a source of Met activity is a fallacy. Numerous refereed publications have demonstrated that DL-HMTBA is equivalent to DL-Met (DLM) as a source of Met activity, including a recent multi-regression analysis of 62 papers in the literature containing over 400 observations for each Met source (Vázquez-Añón et al., 2005). It should be pointed out that this is a much more extensive set of literature than that used in the review referenced by Hoehler (Jansman et al., 2003). Furthermore, the methods used by the Jansman review have been challenged as inappropriate (Kratzer and Littell, 2006). Finally, all of the alleged physiological arguments that attempt to explain the supposed differences in efficacy between DL-HMTBA and DLM have been refuted in peer-reviewed publications (Dibner and Knight, 1984; Knight and Dibner, 1984; Dibner et al., 1987, 1990; Dibner, 2003; Richards et al., 2005).
We are well aware of Hoehler’s position on the efficacy of DL-HMTBA relative to DLM and the tenacity with which he holds it despite overwhelming evidence to the contrary. At its foundation, his position is based on a misunderstanding and misapplication of linear and exponential slope ratio bioavailability methods (Kratzer and Littell, 2006). These methods were developed to estimate the relative bioavailability of the same nutrient in different matrixes (e.g., Lys in wheat, corn, and soybean meal) with a standard of known and preferably high bioavailability (such as Lys-HCl; Ammerman et al. 1995). Thus, once the nutrient is available for absorption, all other aspects of metabolism are identical. When comparing the bioavailability of DLM and DL-HMTBA, the assumptions required for validity of these bioavailability methods cannot be accepted (Kratzer and Littell, 2006). This is because DL-HMTBA and DLM are different molecules: DL-HMTBA is not Met; it is a precursor of Met. As such, DL-HMTBA is metabolized substantially differently than DLM once presented to the animal for absorption (Dibner, 2003; Lobely, 2005). Consequently, DL-HMTBA does not function as a dilution of DLM; rather, the 2 compounds demonstrate different forms of dose responses. For a complete discussion of these differences and the appropriate methodology to use in comparing the sources, the reader is referred to Kratzer and Littel (2006), Vázquez-Añón et al. (2006), and González-Esquerra et al. (2007).
It is true that our paper compared DL-HMTBA from Mintrex with DL-HMTBA from Alimet feed supplement and did not include a DLM treatment (Yi et al., 2007). Nevertheless, the body of published evidence demonstrates that DL-HMTBA from any commercially available source is fully available as a source of Met activity.
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FOOTNOTES |
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Received for publication June 4, 2007. Accepted for publication June 4, 2007.
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REFERENCES |
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 TOP REFERENCES |
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Dibner, J. J. 2003. Review of the metabolism of DL-2-hydroxy-4-methylthiobutanoic acid. World’s Poult. Sci. J. 59:99–110.[ISI]
Dibner, J. J., R. C. Durley, J. G. Kostelc, and F. J. Ivey. 1990. 2-Hydroxy-4-methylthio butanoic acid (HMB) is a naturally occurring methionine precursor in the chick. J. Nutr. 120:553–560.
Dibner, J. J., and C. D. Knight. 1984. Conversion of 2-hydroxy-4-(methylthio) butanoic acid to L-methionine in the chick: A stereospecific pathway. J. Nutr. 114:1716–1723.
Dibner, J. J., C. D. Knight, R. A. Swick, and F. J. Ivey. 1987. Absorption of 2-hydroxy-4-(methylthio)butanoic acid from the hindgut of the broiler chick. Poult. Sci. 67:1314–1321.[ISI]
González-Esquerra, R., M. Vázquez-Añón, T. Hampton, J. Firman, and C. D. Knight. 2007. Evidence of a different dose response in turkeys when fed 2-hydroxy-4(methylthio)butanoic acid versus DL-methionine. Poult. Sci. 86:517–524.
Jansman, A. J. M., C. A. Kan, and J. Wiebenga. 2003. Comparison of the biological efficacy of DL-methionine and hydroxyl-4-methylthiobutanoic acid (HMB) in pigs and poultry. ID-Lelystad No. 2209. Cent. Bur. Livest. Feed., Lelystad, the Netherlands.
Knight, C. D., and J. J. Dibner. 1984. Comparative absorption of 2-hydroxy-4-(methylthio)-butanoic acid and L-methionine in the broiler chick. J. Nutr. 114:2179–2186.
Kratzer, D. D., and R. C. Littell. 2006. Appropriate statistical methods to compare dose responses of methionine sources. Poult. Sci. 85:947–954.
Lobley, G. E., T. J. Wester, A. G. Calder, D. S. Parker, J. J. Dibner, and M. Vázquez-Añón. 2006. Absorption of 2-hydroxy-4-methylthiobutyrate (HMTBA) and conversion to methionine in lambs. J. Dairy Sci. 89:1072–1080.
Richards, J. D., C. A. Atwell, M. Vázquez-Añón, and J. J. Dibner. 2005. Comparative in vitro and in vivo absorption of 2-hydroxy-4(methylthio) butanoic acid and methionine in the broiler chicken. Poult. Sci. 84:1397–1405.
Vázquez-Añón, M., R. González-Esquerra, E. Saleh, T. Hampton, S. Ricther, J. Firman, and C. D. Knight. 2006. Evidence for 2-hydroxy-4-methylthio butanoic acid and DL-methionine having a different dose-response in growing broilers. Poult. Sci. 85:1409–1420.
Vázquez-Añón, M., D. Kratzer, R. Gonzalez-Esquerra, I. G. Yi, and C. D. Knight. 2005. A multiple regression model approach to contrast the performance of 2-hydroxy-4-methylthio butanoic acid and DL-methionine supplementation tested in broiler experiments and reported in the literature. Poult. Sci. 85:693–705.[ISI]
Yi, G. F., C. A. Atwell, J. A. Hume, J. J. Dibner, C. D. Knight, and J. D. Richards. 2007. Determining the methionine activity of Mintrex organic trace minerals in broiler chickens by using radiolabel tracing or growth assay. Poult. Sci. 86:877–887.
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