Table 4. Pre- and post-weaning rumen mean values of rumen pH, ammonia nitrogen (Ammonia-N) and volatile fatty acids (VFA) of control heifers (CON) and heifers supplemented with essential oils blend (BEO) in milk replacer during pre-weaning.

Item	Treatment		SEM	P–value3
	CON1 (n = 15)	BEO2 (n = 14)		T	W	T x W
Pre-weaning (4 to 60 d)
Rumen pH	5.99	5.85	0.52	0.37	0.03	0.06
Rumen ammonia-N (mg/dL)	11.40	13.80	0.03	0.15	<0.001	0.37
Rumen VFA (μmol/mL)
Acetic (C2)	30.80	27.16	8.15	0.24	<0.001	0.14
Propionic (C3)	18.88	20.01	7.11	0.59	<0.001	0.14
Butyric (C4)	0.80	0.80	0.08	0.83	0.005	0.98
C2:C3	1.97	1.69	0.12	0.05	<0.001	0.95
Post-weaning (61 to 90 d)
Rumen pH	6.19	5.90	0.001	0.05	0.001	0.86
Rumen ammonia-N (mg/dL)	10.97	9.53	9.03	0.17	0.91	0.88
Rumen VFA (μmol/mL)
Acetic (C2)	38.32	39.03	8.48	0.81	0.006	0.93
Propionic (C3)	28.27	30.69	5.16	0.41	0.003	0.75
Butyric (C4)	5.94	6.16	1.19	0.82	0.95	0.62
C2:C3	1.43	1.23	0.20	0.006	0.74	0.93

¹CON = control

²BEO = 1 g/calf/d blend of essential oil.

³T = treatment effect; W = week effect, T x W = treatment by week interactions.