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LETTER TO THE EDITOR |
Degussa Corp., Kennesaw, GA 30144
1 Corresponding author: dirk.hoehler{at}degussa.com
Recently, Vazquez-Anon et al. (2006) published a paper in Poultry Science suggesting evidence for DL-2-hydroxy-4-(methylthio) butanoic acid (DL-HMTBA) and DL-Met (DL-M) having different dose responses in growing broilers. The authors concluded that the 2 Met sources "have a different dose-response form, DL-HMTBA could outperform DL-M at commercial levels, and DL-M could outperform DL-HMTBA at deficient levels." Additionally, it is suggested that relevant comparisons between the 2 Met sources should be conducted "at levels of commercial use." These conclusions and suggestions are incorrect and misleading.
When comparing essential nutrients or different sources of the same nutrient (L-Met in the present case), one should always evaluate the complete dose-response curve, starting with a deficient basal diet, followed by several incremental levels of the nutrients to be tested. Depending on the data structure of the respective dose-response trial, slope-ratio (linear response) or nonlinear models should be applied. These models can be used for estimation of comparative bioefficacy or bioavailability of any nutrients, such as P (Potter et al., 1995) or Fe (Boling et al., 1998).
A simple example based on broiler weight gain data by Lemme et al. (2002) shall be used to demonstrate the statements above vs. the incorrect methodology and conclusions of Vazquez-Anon et al. (2006). Two Met sources, DL-M and diluted DL-M (65%, a product representing an internal standard with a known "relative efficacy" of 65%), were added at incremental levels to a Met-deficient commercial-type diet (Table 1
). Using the proper exponential regression method to analyze the data sets, diluted DL-M (65%) had a calculated relative efficacy of 60% relative to DL-M (Lemme et al., 2002), confirming the validity of the used statistical method. Using a completely different approach to evaluate the data, the relative response rate of the basal diet was 64% of the maximum response (see Table 1). The relative response rates for the 0.06, 0.12, 0.18, and 0.24% supplemented DL-M levels were 84, 94, 99, and 100%, whereas the relative response rates for diluted DL-M (65%) were 76, 86, 91, and 98%. Hypothetically, several different "effectiveness figures" were generated in this example, with the response rates of the 2 products merging with increasing Met levels following the law of diminishing returns. Maximum weight gain can, theoretically, be achieved with high(er) supplementation levels of both products, even knowing that 1 product contains only 65% of Met, independent of supplemental level. To describe the results of the example by Lemme et al. (2002), using the wording of Vazquez-Anon et al. (2006) would be as follows: "DL-M outperforms diluted DL-M (65%) at deficient levels, whereas both products perform similar under commercial levels," underlining how unsound and misleading such an approach would be.
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Received for publication August 23, 2006. Accepted for publication August 23, 2006.
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REFERENCES |
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 TOP REFERENCES |
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Lemme, A., D. Hoehler, J. J. Brennan, and R. F. Mannion. 2002. Relative effectiveness of methionine hydroxyl analog compared to DL-methionine in broiler chickens. Poult. Sci. 81:838–845.
Potter, L. M., M. Potchanakorn, V. Ravindran, and E. T. Kornegay. 1995. Bioavailability of phosphorus in various phosphate sources using body weight and toe ash as response criteria. Poult. Sci. 74:813–820.[ISI][Medline]
Vazquez-Anon, M., R. Gonzalez-Esquerra, E. Saleh, T. Hampton, S. Ritcher, J. Firman, and C. D. Knight. 2006. Evidence for 2-hydroxy-4(methylthio) butanoic acid and DL-methionine having different dose responses in growing broilers. Poult. Sci. 85:1409–1420.
This article has been cited by other articles:
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  G. D. Rosen Nutritive Values of Methionine Sources Poult. Sci., February 1, 2007; 86(2): 209 - 210. [Full Text] [PDF]
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