Table 3.

Rumen pH, volatile fatty acids (VFA), and apparent digestibility of lactating cows selected for phenotypic divergence in residual feed intake (RFI)

Items	Low RFI	High RFI	SEM	P valuea
				RFI	Day	RFI × Day
pH	6.41	6.30	0.08	0.35	0.54	0.86
Total VFA, mmol/L	101	108	3.84	0.18	0.21	0.22
Molar proportion, mmol/100 mmol
Acetate (A)	65.1	64.2	0.86	0.46	0.28	0.61
Propionate (P)	20.2	21.5	0.94	0.36	0.08	0.40
Butyrate	11.1	10.8	0.39	0.71	0.17	0.87
Isobutyrate	0.72	0.68	0.04	0.44	< 0.01	0.43
Valerate	1.45	1.45	0.05	0.98	< 0.01	0.30
Isovalerate	1.45	1.30	0.08	0.21	0.06	0.71
A: P ratio	3.29	3.11	0.18	0.46	0.07	0.40
Apparent digestibilityb
DM, %	64.0	64.4	0.87	0.73	0.12	0.43
CP, %	65.4	66.2	1.55	0.73	0.24	0.69
NDF, %	35.9	35.4	1.02	0.74	0.02	0.22
ADF, %	33.7	32.9	1.06	0.60	0.30	0.28

^aP value associated with RFI, time, and the interaction of RFI and time

^bDM dry matter, CP crude protein, NDF neutral detergent fiber, ADF acid detergent fiber