Abstract
Numerous empirical and mechanistic models predicting methane (CH4) production are available. The aim of this work was to evaluate the Molly cow model and the Nordic cow model Karoline in predicting CH4 production in cattle using a data set consisting of 267 treatment means from 55 respiration chamber studies. The dietary and animal characteristics used for the model evaluation represent the range of diets fed to dairy and growing cattle. Feedlot diets and diets containing additives mitigating CH4 production were not included in the data set. The relationships between observed and predicted CH4 (pCH4) were assessed by regression analysis using fixed and mixed model analysis. Residual analysis was conducted to evaluate which dietary factors were related to prediction errors. The fixed model analysis showed that the Molly predictions were related to the observed data (± standard error) as CH4 (g/d) = 0.94 (±0.022) × pCH4 (g/d) + 31 (±6.9) [root mean squared prediction error (RMSPE) = 45.0 g/d (14.9% of observed mean), concordance correlation coefficient (CCC) = 0.925]. The corresponding equation for the Karoline model was CH4 (g/d) = CH4 (g/d) = 0.98 (±0.019) × pCH4 (g/d) + 7.0 (±6.0) [RMSPE = 35.0 g/d (11.6%), CCC = 0.953]. Proportions of mean squared prediction error attributable to mean and linear bias and random error were 10.6, 2.2, and 87.2% for the Molly model, and 1.3, 0.3, and 98.6% for the Karoline model, respectively. Mean and linear bias were significant for the Molly model but not for the Karoline model. With the mixed model regression analysis RMSPE adjusted for random study effects were 10.9 and 7.9% for the Molly model and the Karoline model, respectively. The residuals of CH4 predictions were more strongly related to factors associated with CH4 production (feeding level, digestibility, fat concentrations) with the Molly model compared with the Karoline model. Especially large mean (underprediction) and linear bias (overprediction of low digestibility diets relative to high digestibility diets) contributed to the prediction error of CH4 yield with the Molly model. It was concluded that both models could be used for prediction of CH4 production in cattle, but Karoline was more accurate and precise based on smaller RMSPE, mean bias, and slope bias, and greater CCC. The importance of accurate input data of key variables affecting diet digestibility is emphasized.
Highlights
Methane (CH4) is a greenhouse gas contributing to global climate change
The effect of DMI on CH4 yield per 1 kg increase in DMI was stronger [−0.28 ± 0.034; P < 0.001 vs. −0.09 ± 0.041; P = 0.03] for the Karoline model compared with the Molly model
We evaluated the performance of both the Karoline and Molly models to predict CH4 production
Summary
Methane (CH4) is a greenhouse gas contributing to global climate change. Methane production in ruminants is associated with energy losses, the amount depending on the type of diet and intake level (Johnson and Johnson, 1995). As the direct measurement of CH4 (e.g., in respiration chamber) is relatively expensive and labor intensive, numerous empirical equations (Blaxter and Clapperton, 1965; Moe and Tyrrell, 1979) and mechanistic models (Benchaar et al, 1998; Mills et al, 2001; Kebreab et al, 2008) to predict CH4 production are reported in the literature. Sometimes the models predicting CH4 production are evaluated using rather small data sets (Axelsson, 1949; Blaxter and Clapperton, 1965), or data from a single laboratory (Yan et al, 2000; Jentsch et al, 2007) and in some cases the data do not cover a wide range of intake and diet composition (Moate et al, 2011). We chose 2 models originally compiled to predict nutrient absorption from the digestive tract and metabolized in various tissues, to test their performance in predicting CH4 production by cattle
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