Ruminal pH predictions for beef XXXX : Comparative evaluation of current models.

@entity558 @entity981 @entity3265 @entity598 @entity16235 @entity291
This study evaluated 8 empirical models for their ability to accurately predict mean ruminal pH in beef @entity291 fed a wide range of diets. Models tested that use physically effective fiber (peNDF) as a dependent variable were Pitt et al. (1996, @entity558 ), Mertens (1997, MER), Fox et al. (2004, FOX), Zebeli et al. (2006, ZB6), and Zebeli et al. (2008, ZB8), and those that use rumen VFA were Tamminga and Van Vuuren (1988, @entity16235 ), Lescoat and Sauvant (1995, LES), and Allen (1997, @entity981 ). A data set of 65 published papers (231 treatment means) for beef @entity291 was assembled that included information on animal characteristics, diet composition, and ruminal fermentation and mean pH. Model evaluations were based on mean square prediction error (MSPE), concordance correlation coefficient (CCC), and regression analysis. The prediction potential of the models varied with low root MSPE (RMSPE) values of 4.94% and 5.37% for @entity558 and FOX, RMSPE values of 9.66% and 12.55% for ZB6 and MER, and intermediate RMSPE values of 5.66% to 6.26% for the other models. For @entity558 and FOX, with the lowest RMSPE, approximately 96% of MSPE was due to random error, whereas for ZB6 and MER, with the highest RMSPE, 15.85% and 23.42% of MSPE, respectively, was due to linear bias, and 37.19% and 60.12% of the error, respectively, was due to deviation of the regression slope from unity. The CCC was greatest for @entity558 (0.67) and FOX (0.62), followed by 0.60 for LES and @entity16235 , 0.52 for ZB8, 0.39 for MER, 0.34 for @entity981 , and 0.22 for ZB6. Residuals plotted against model-predicted values showed linear bias (P < 0.001) for all models except @entity558 (P = 0.976) and FOX (P = 0.054) and mean bias (P < 0.001) except for FOX (P = 0.293), LES (P = 0.215), and @entity16235 (P = 0.119). The study showed that the empirical models @entity558 and FOX, based on peNDF, and LES and @entity16235 , based on VFA, are preferred over the others for prediction of mean ruminal pH in beef @entity291 fed a wide range of diets. Several animal (BW and intake), diet (forage and OM contents), and ruminal ( @entity3265 and @entity598 concentrations) factors were (P < 0.001) related to the residuals for each model. We conclude that the accuracy of prediction of mean ruminal pH was relatively low for all extant models. Consideration of factors in addition to peNDF and total VFA, as well as the use of data from studies with continuous measurement of ruminal pH over 24 h or more, would be useful in the development of improved models for predicting ruminal pH in beef @entity291 .
