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LETTER TO THE EDITOR |
Holo-Analysis Services Ltd., London SW19 5PH, United Kingdom
1 Corresponding author: g.d.rosen{at}btinternet.com
Kratzer and Littell (2006) recently used the test results of a small selection of 13 published broiler studies to elaborate nonlinear separate plateau asymptotic regression models in order to compare dose responses of DL-Met (DLM) and DL-2-hydroxy-4-methylthio butanoic acid (HMTBA). They presented detailed evidence for their conclusion that "separate plateau models should be used when comparing these 2 products"(Kratzer and Littell, 2006, p. 947).
Piepho (2006) responded thereto in a cautionary note on appropriate statistical methods and concluded that "the evidence of a difference in plateaus based on the meta-analysis in Kratzer and Littell (2006) is weaker than stated in the paper" (p. 1512). He also recommended that "it would be very desirable to be able to include more studies and possibly to use more powerful methods of meta-analysis" (Piepho, 2006, p. 1512).
Both these conclusions are, however, open to question. In nutrition theory and praxis, nutrient response curves are inevitably quadratic. Nutrient requirements are maxima not plateaus. Plateau models are therefore abiological and incorrect.
Notwithstanding his introductory thesis that "one should always evaluate the complete dose-response curve," (Hoehler, 2006, p. 2047) a similar fallacy is manifest in Hoehler’s (2006) recent use of data from Lemme et al.’s (2002) exponential broiler weight gain regression models in order to refute Vazquez-Anon et al.’s (2006a) conclusions on supplementary DLM versus HMTBA.
To resolve this 54-yr-old debate on the relative nutritive values of supplementary Met sources, I would recommend that further research in this field should include the following: 1) compilation of holistic databases, 2) gravimetric product comparisons, 3) quadratic dosage terms, 4) holo-analysis of all available independent variables, and 5) subdivision of test resources only for statistically significantly different subclasses. Straightforward gravimetric comparisons are needed in order to exclude any bias from differences in multifunctionality, i.e. DLM is bifunctional (nutrient and prenutrient) and HMTBA is trifunctional (prenutrient, prenutrient, and strong organic acid).
Nutritive values with confidence limits, unique in time and place, could be computed for both candidates from individual holo-analytical models for their specific effects on feed intake, liveweight gain, mortality, carcass qualities, and N pollutions. These differential responses could then be integrated in overall economic nutritive values (Rosen, 1999) to value and compare DLM and HMTBA at current prices. Such comparisons could determine new prices for DLM and HMTBA, affording identical efficiency in animal nutrition.
A first step in this direction has recently been reported by Vazquez-Anon et al (2006). In their meta-analysis of experiments in 62 publications, they collected 411 DLM and 427 HMTBA observations for analysis of gain and feed conversion responses in terms of 35 independent variables. Their models were finally based on 274 to 275 DLM and 278 to 282 HMTBA observations due to the absence of missing variables in test reports and accounted for 51 to 87% of variations in responses.
En route to an eventual holo-analysis, this research has provided the following: a) clear-cut evidence of quadratic responses with maxima for the 2 products at 0.25 to 0.28% supplementation of a basal dietary Met content of 0.28% and b) firm indications of no significant gain or feed conversion differences between DLM and HMTBA under historic research conditions used up to 2005 together with the likelihood of no significant differences between DLM and HMTBA in US usage in practice (Agri Stats Inc., 2004).
Received for publication October 24, 2006. Accepted for publication October 24, 2006.
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REFERENCES |
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 TOP REFERENCES |
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Hoehler, D. 2006. No evidence for different dose-responses of commercial methionine sources in broilers. Poult. Sci. 85:2047.
Kratzer, D. D., and R. C. Littell. 2006. Appropriate statistical methods to compare dosage responses of methionine sources. Poult. Sci. 85:947–954.
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.
Piepho, H. -P. 2006. A cautionary note on appropriate statistical methods to compare dose-responses of methionine sources. Poult. Sci. 85:1511–1512.
Rosen, G. D. 1999. Nutritive value re-visited. A definition. Page 373 in Proc. 12th Eur. Symp. Poult. Nutr. WPSA, Veldhoven, The Netherlands.
Vazquez-Anon, M., R. Gonzalez-Esquerra, E. Saleh, T. Hampton, S. Ritcher, J. Firman, and C. D. Knight. 2006a. Evidence for 2-hydroxy-4(methylthio) butanoic acid and DL-methionine having different dose responses in growing broilers. Poult. Sci. 85:1409–1420.
Vazquez-Anon, M., D. Kratzer, R. Gonzalez-Esquerra, I. G. Yi, and C. D. Knight. 2006b. 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.
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  N. Sauer, K. Emrich, H.-P. Piepho, A. Lemme, M. S. Redshaw, and R. Mosenthin Meta-Analysis of the Relative Efficiency of Methionine-Hydroxy-Analogue-Free-Acid Compared with DL-Methionine in Broilers Using Nonlinear Mixed Models Poult. Sci., October 1, 2008; 87(10): 2023 - 2031. [Abstract] [Full Text] [PDF]
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C. G. Scanes Ethics of Publication: Is Publication an Obligation for Researchers? Poult. Sci., October 1, 2007; 86(10): 2051 - 2052. [Full Text] [PDF]
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