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. 2015 Sep 2;1(3):128–134. doi: 10.1016/j.aninu.2015.08.015

Table 3.

Linear equations obtained for CH4 production (L/d) when using mixed models with CO2 (L/d) or O2 (L/d), physiological state and dietary variables.1,2

Equations AIC σexpt σres R2 Eq.
CH4 Created by potrace 1.16, written by Peter Selinger 2001-2019 17 (13.9) + 0.0787 (0.00166) CO2+19 (8.7) if Phys1 8,373 38.4 35.1 0.93 1a
CH4 Created by potrace 1.16, written by Peter Selinger 2001-2019 −12 (18.4) + 0.0802 (0.00165) CO2+19 (8.5) if Phys1+Inline graphic 8,324 36.9 34.2 0.94 1b
CH4 Created by potrace 1.16, written by Peter Selinger 2001-2019 −33 (18.5) + 0.0804 (0.00169) CO2+19 (8.6) if Phys1+166.3 (40.28) ADF 8,349 38.7 34.6 0.93 1c
CH4 Created by potrace 1.16, written by Peter Selinger 2001-2019 −49 (19.9) + 0.0808 (0.00170) CO2+19 (8.6) if Phys1+128.5 (27.43) NDF 8,345 39.0 34.5 0.93 1d
CH4 Created by potrace 1.16, written by Peter Selinger 2001-2019 56 (17.6) + 0.0720 (0.00214) O2+24 (11.2) if Phys1 8,802 47.8 45.3 0.86 2a
CH4 Created by potrace 1.16, written by Peter Selinger 2001-2019 24 (23.1) + 0.0727 (0.00214) O2+24 (11.1) if Phys1+Inline graphic 8,772 44.5 45.1 0.87 2b

AIC = Akaike information criterion, ADF = acid detergent fibre, NDF = neutral detergent fibre.

1

Each predictor had a significant effect (P < 0.05 or less, Wald tests) on the relationship and the data in brackets are standard errors.

2

Physi = physiological state (i = 1 for lactating cows, i = 0 for dry cows and young cattle), FPi = forage proportion (i = 1 for FP ≤ 25%, i = 2 for 25% < FP ≤ 50%, i = 3 for 50% < FP ≤ 75% and i = 4 for FP > 75%), units for ADF and NDF are kg/kg DM, reference levels for the categorical variables correspond to Phys0 and FP1.σexpt and σres, where σ = standard deviation for the random effects (expt: experiment and res: residuals). The standard deviation for "cow within experiment” was 23.0 on average for models with CO2 and 23.2 for models with O2, which is large enough compared to σres to justify its inclusion in the models.R2 values were obtained from regression analyses, after adjusting CH4 observations for the experiment effect.