Appropriate Statistical Methods to Compare Dose Responses of Methionine Sources

Abstract

Two sources of methionine (Met) activity are frequently used in commercial feed formulation: DL-2-hydroxy-4-(methylthio) butanoic acid (HMTBA), most commonly available as an 88% solution with 12% water; and DL-methionine (DLM, 99% powder). Despite the fact that both compounds have been in commercial use for over 50 yr, controversy and confusion remain with respect to their relative bioefficacy (RBE). This paper presents a review of the use of a nonlinear common plateau asymptotic regression technique (NLCPAR) that has been used to compare the 2 Met sources with particular emphasis on the validity of the basic assumptions of that model. The thesis of this paper is that the controversy is due, at least in part, to the misapplication of this regression technique to estimate the RBE of HMTBA and DLM. The NLCPAR model is a bioassay with the key dependent assumptions that HMTBA is a dilution of DLM, and that each follows dose-response curves of the same form and approach a common plateau. Because both provide Met activity, it may be considered reasonable to accept these assumptions; however, specifically testing them demonstrated that the assumption of a common dose-response is not supported by data. The common plateau assumption was tested with an alternative approach of fitting nonlinear separate plateaus asymptotic regression (NLSPAR) to a set of 13 published broiler studies in which the NLCPAR model had been used to estimate RBE of HMTBA and DLM. The hypothesis of a common plateau was rejected (P < 0.01), meaning that the conclusion that HMTBA had lower bioefficacy than DLM based on the NLCPAR methodology was not valid. An example using published data demonstrated that the NLSPAR model was a significantly better fit than the NLCPAR model, and showed that HMTBA and DLM followed different dose responses. Consequently, there was no single value for RBE for the entire dose range; rather, the RBE of the 2 compounds varied with use level. The evidence presented here indicates that separate plateau models should be used when comparing these 2 products. These more valid models can then be used for predictions of differences between HMTBA and DLM at levels of expected use.

Продуктивність Та Забійні Якості Перепелів При Використанні Різних Джерел Метоніну В Раціонах

“…Тварині не потрібно витрачати додаткові життєві ресурси та енергії для переведення частини D-метіоніну в L-метіонін. Виходячи з отриманих в ході досліджень даних (Jiao et al, 2010;Kratzer, Littell, 2006;Kubińska et al, 2014;Liu et al, 2010;Mitchell, Lemme, 2008;Narayanswamy, Bhagwat, 2010;Paulicks et al, 2009;Sangali et al, 2014;Vazquez-Anon et al, 2006;Yi et al, 2007), очевидно, що джерела метіоніну мають різну ефективність. Тому метою наших досліджень було визначити вплив різних джерел метіоніну у комбікормах на продуктивність та забійні якості перепелів м'ясного напряму продуктивності.…”

Bioavailability of liquid methionine hydroxy analogue-free acid relative to DL-methionine in broilers

“…This assumption has been questioned by Kratzer and Littell (2006) who suggested to use two separate models (with diff erent asymptotes) when comparing DLM and MHA availability. In contrast, Piepho (2006) considered the conclusions by Kratzer and Littell (2006) not fully justifi ed from a statistical point of view.…”

“…This assumption has been questioned by Kratzer and Littell (2006) who suggested to use two separate models (with diff erent asymptotes) when comparing DLM and MHA availability. In contrast, Piepho (2006) considered the conclusions by Kratzer and Littell (2006) not fully justifi ed from a statistical point of view. To confront these two approaches, separate exponential models were fi tted to carcass and breast meat yield data (recalculated to equimolar basis) obtained in the present study as suggested by Kratzer and Littell (2006).…”

Bioavailability of different methionine sources for broilers from 1 to 21 days old

“…Furthermore, the correct statistical design to evaluate the bioavailability of different sources of essential nutrients has been under debate (Littell et al, 1997;Kratzer and Littell, 2006;Piepho, 2006). A standardized method of statistical analysis would make comparisons of experiments assessing different sources of nutrients easier and more accurate (Littell et al, 1997).…”