Table 5.

Seven models, used to predict methane yield (MY, g methane/kg dry matter intake) from ruminal acetate (A), propionate (P), and butyrate (B) expressed as mol/100 mol total volatile fatty acid, and the concentration of propionate in ruminal fluid ([P], mmol/L). Their coefficients ¹ and constants ² were estimated by fitting the models to training data, pooled from seven experiments by meta-analysis. Root-mean-square error of prediction (RMSEP, g CH₄/kg dry matter intake) and Lin’s concordance (CCC) were calculated by a leave-one-experiment-out cross-validation procedure. These were used to calculate rank (1 = minimum RMSEP, maximum CCC) of equations tested.

Equation Number	Model	Estimates ± S.E.	RMSEP	CCC	Rank
(1c)	MY = 16 × (0.50A − 0.25P + 0.50B) × c/100	c = 3.98 ± 0.15	3.7	0.52	4
(2)	MY = dA − eP + fB	d = 0.30 ± 0.042, e = 0.22 ± 0.055, f = 0.48 ± 0.16	3.6	0.63	4
(3)	MY = g(A/P) + h	g = 4.08 ± 0.36, h = 7.05 ± 1.40	3.2	0.69	1
(4)	MY = i(A+B)/P + j	i = 3.28 ± 0.29. j = 7.60 ± 1.28	3.2	0.70	1
(5)	MY = kP + m	k =−0.57 ± 0.057, m = 32.3 ± 1.4	3.5	0.63	4
(6)	MY = n[P] + q	n =−0.24 ± 0.035, q = 26.1 ± 1.3	4.2	0.36	7
(7)	MY = s/P + t	s = 316 ± 28, t = 4.4 ± 1.5	3.2	0.70	1

¹ Coefficient c has units of moles of total VFA/kg DMI, coefficients d, e, f, k, and q have units of g CH₄·kg DMI⁻¹·moles⁻¹·100 moles total VFA, the coefficients g, and i have units of g CH₄·kg DMI⁻¹ and the coefficient m has units of g CH₄·kg DMI⁻¹·L·mmol⁻¹. ² Constants h, j, l, n, and s have the units of g CH₄·kg DMI⁻¹.