More and more countries have banned the use of antibiotic growth promoters in livestock nutrition stimulating the neo-investigation for natural alternative additives. The objectives of this study were (i) to compare the effects of monensin sodium (MO), botanical extracts (BE) and its combination with a yeast product (BE+LY) on dairy cow performance by determining their effect on rumen pH and general rumen fermentation and (ii) to determine whether natural alternatives have the potential to replace ionophores as the primary fermentation altering feed additive for lactating Jersey cows. Four rumen cannulated lactating Jersey cows were used in a 4 × 4 Latin square design experiment. The 4 experimental treatments were: 1) Control (C), a lucerne hay/maize based TMR (10.7 MJ ME/kg, 17% CP, 32.1% NDF), 2) MO (15 mg/kg of Rumensin, Elanco Animal Health), 3) BE (1g/d/cow, Oleobiotec, Laboratoire PHODE, France) and 4) BE + LY (group 3 combined with 1x1010CFU yeast (Saccharomyces cerevisiae CNCM I-1077)/d/cow. The experimental periods were 25 d with the last 4 d for milk performance, rumen sampling and the in sacco nutrient disappearance. Results (Table 1) suggest that the tested BE has potential to be a natural alternative to ionophore antibiotics in dairy diets. Table 1. Effect of feed additives

Parameter	C	MO	BE	BE + LY	SEM
DMI (kg/d)	22.0cd	21.3d	22.7c	22.3cd	0.5
Milk production (kg/d)	22.9cd	22.4d	23.2c	23.4c	0.37
Fat %	4.32b	4.45ab	4.52a	4.46ab	0.05
Protein %	3.93	3.93	3.91	3.91	0.25
Rumen fermentation parameters measured at 1400 h (7 h post-feeding)
Ruminal pH	6.02d	6.28c	6.30c	6.10c	0.09
Total VFA (mmol/L)	120.6cd	106.4d	128.1c	121.7cd	6.52
In sacco disappearance (%)
NDF 24 h (Lucerne)	50.6d	51.8cd	54.7c	50.6d	1.35
Starch 24 h (TMR)	90.5b	93.1ab	95.7a	90.2b	1.55
N-nitrogen 24 h (TMR)	84.5ab	85.1a	84.8a	82.8b	0.50

Means in the same row without a common superscript differs (^abP < 0.05; ^cdP < 0.1).