Methodological factors affecting gas and methane production during in vitro rumen fermentation evaluated by meta-analysis approach

Table 5 Outcome of the backward stepwise multivariate regression analysis on predicted values obtained by correcting for the study effect and adjusting raw data for different accuracies^a of the total gas production (GP), methane (CH₄) production and proportion (% CH₄ on total GP)

Items	GP, mL/g DM		CH₄, mL/g DM		CH₄, % on total GP
Items	estimate ± SE	P	estimate ± SE	P	estimate ± SE	P
Intercept	141.0 ± 5.24	<0.01	21.8 ± 2.22	<0.01	15.0 ± 0.31	<0.01
Pressure^b	-	-	-	-	0.9 ± 0.17	<0.01
Incubation time^c	7.9 ± 3.30	0.018	4.2 ± 1.40	<0.01	-	-
Collection time^d	26.4 ± 3.21	<0.01	9.0 ± 1.37	<0.01	1.2 ± 0.19	<0.01
Donor species^e	32.9 ± 3.95	<0.01	5.3 ± 1.68	<0.01	-	-
N in the buffer^f	24.7 ± 3.86	<0.01	6.7 ± 1.64	<0.01	0.7 ± 0.23	<0.01
BRF/FS^g	7.7 ± 1.59	<0.01	3.3 ± 0.67	<0.01	0.3 ± 0.10	<0.01
NDF, g/kg DM^h	−0.02 ± 0.007	<0.01	−0.009 ± 0.0031	<0.01	-	-
R^b	0.48		0.34		0.27
Max VIFⁱ	1.76		1.76		1.77
Max condition index^j	11.11		11.11		11.88

^aAdjustment for different accuracies of measurements in different studies was carried out by weighing raw data by the inverse of the squared standard error divided by the mean of all the squared standard errors (St-Pierre, 2001 [20])
^bclass 0 = constant or class 1 = increasing pressure
^cclass 0 = 24 h; class 1 = ≥ 48 h of incubation
^dclass 0 = before feeding of donor animals or at slaughterhouse; class 1 = after feeding of donor animals
^especies used as donor of rumen fluid; class 0 = sheep; class 1 = bovine
^fclass 0 = presence; class 1 = absence of N in the buffer
^gBRF/FS = (buffered rumen fluid and feed sample ratio) class 0 = <130 mL/g DM; class 1 = 130–140 mL/g DM; class 2= >140 mL/g DM)
^hactual NDF content of feed sample used: treated as continuous variable
ⁱVIF = variance inflation index. When value is less than 10, the predictor variables show no significant multicollinearity
^jcollinearity index. When value is less than 30, the variables tested are independent

ISSN: 2049-1891