Table 4.
Measures of predictive ability of MollyRum14 for methane yield (g CH4/kg DMI) from sheep fed varying forages (sole diet), and the effect of substrate degradation rate (SLOW, MOD, or FAST) and fermentation stoichiometry (FS = 0 favors a more acetogenic fermentation, FS = 0.5 intermediate, FS = 1.0 favors a more propionogenic fermentation)
| Variable | SLOW | Substrate degradation rate | FAST | ||||||
|---|---|---|---|---|---|---|---|---|---|
| MOD | |||||||||
| FS | |||||||||
| 0.0 | 0.5 | 1.0 | 0.0 | 0.5 | 1.0 | 0.0 | 0.5 | 1.0 | |
| Mean observed | 19.3 | 19.3 | 19.3 | 19.3 | 19.3 | 19.3 | 19.3 | 19.3 | 19.3 |
| Mean predicted | 18.0 | 17.2 | 16.3 | 18.7 | 17.9 | 17.2 | 18.9 | 18.1 | 17.4 |
| Mean bias | −1.3 | −2.1 | −3.0 | −0.6 | −1.4 | −2.1 | −0.4 | −1.15 | −1.9 |
| RPE1 | 19.2 | 21.2 | 23.9 | 16.8 | 18.2 | 20.3 | 16.3 | 17.5 | 19.6 |
| Error decomposition: | |||||||||
| % bias | 13.1 | 27.3 | 41.4 | 3.3 | 14.9 | 29.6 | 1.5 | 11.6 | 26.4 |
| % slope | 9.8 | 8.0 | 6.0 | 7.5 | 6.6 | 5.1 | 6.2 | 5.8 | 4.6 |
| % random | 77.1 | 64.6 | 52.5 | 89.2 | 78.5 | 65.2 | 92.4 | 82.6 | 69.0 |
| R 22 | 0.54 | 0.52 | 0.51 | 0.59 | 0.58 | 0.56 | 0.60 | 0.59 | 0.57 |
| CCC3 | 0.55 | 0.49 | 0.42 | 0.66 | 0.62 | 0.56 | 0.69 | 0.65 | 0.59 |
| RSR4 | 0.77 | 0.85 | 0.95 | 0.67 | 0.73 | 0.81 | 0.65 | 0.70 | 0.78 |
N = 43.
1RPE: Relative prediction error = (Root mean square prediction error RMSPE/mean observed) × 100. An RPE value of <10% indicates good predictive ability, between 10% and 20% reasonable predictive ability, and >20% poor predictive ability.
2 R 2 of the regression predicted vs. observed.
3Lin’s concordance correlation coefficient (closer to 1 is better).
4Ratio of RMSPE to standard deviation of observed values: <0.5, very good prediction; 0.5–0.75, good prediction; 0.75–1, moderate prediction; and >1.0, model needs improvement.