Influence of main dietary chemical constituents on the in vitro gas and methane production in diets for dairy cows

Table 2 Effect of diets and incubation time on pH, ammonia N concentration, volatile fatty acid production (VFA) and molar proportions of acetate, propionate, butyrate and other VFA

	pH	Ammonia N, mg/L	VFA, mmoL/L	Acetate (Ac), % VFA	Propionate (Pr), % VFA	Ac:Pr	Butyrate, % VFA	Other VFA, % VFA
Diet
Reference	6.87	202	5.08	56.1	23.5	2.40	16.0	4.47
Low NDF	6.88	192	5.37	55.8	23.7	2.36	16.2	4.29
High NDF	6.90	223^A	4.44	58.5^A	23.1	2.53	13.3^B	4.26^B
Low CP	6.85	171	5.06	56.0	24.3	2.31	16.1	3.71^B
High CP	6.87	222^A	4.89	57.2	22.8	2.51	14.6	4.85^A
Low lipid	6.87	207	4.96	56.4	23.7	2.39	15.5	4.26^B
High lipid	6.90	197	4.99	56.7	23.5	2.41	15.4	4.36
SEM	0.043	28.5	0.231	0.25	0.64	0.062	0.91	0.158
P-value	0.46	0.008	0.25	<0.001	0.06	0.001	0.002	<0.001
P-value of contrasts
Low vs High NDF	0.99	0.44	0.23	<0.001	0.99	0.001	0.004	0.99
Low vs High CP	0.99	0.014	0.99	0.048	0.048	<0.001	0.99	<0.001
Low vs High lipid	0.99	0.99	0.99	0.99	0.99	0.65	0.99	0.99
Incubation time
24 h	6.95	202	4.47	57.2	22.9	2.50	15.8	3.87
48 h	6.80	202	5.47	56.1	24.1	2.33	14.7	4.76
SEM	0.055	38.7	0.123	0.13	0.82	0.077	1.15	0.201
P-value	0.31	0.99	0.029	0.026	0.39	0.26	0.58	0.09
RMSE	0.032	17.5	0.462	0.49	0.60	0.112	0.87	0.147

Values with different superscripts within column are significantly (P < 0.05) higher (A) or lower (B) compared to the reference diet (containing 361, 158, and 33 g/kg DM of NDF, CP, and lipids)
Low NDF low NDF diet (325 g/kg DM); High NDF high NDF diet (435 g/kg DM), Low CP low protein diet (CP, 115 g/kg DM), High CP high protein diet (CP, 194 g/kg DM), Low lipid low lipid diet (EE, 26 g/kg DM), High lipid high lipid diet (EE, 61 g/kg DM)

ISSN: 2049-1891