Effects of plant extract supplementation on rumen fermentation and metabolism in young Holstein bulls consuming high levels of concentrate

Ninety male Holstein bulls were used in a complete randomized design to study the effects of a blend of plant extract (PE: cynarin, gingsen and fenugreek; Biostar®, Phytosynthese, France) supplementation on performance, rumen fermentation, and metabolism of Holstein bulls fed high-concentrate diets. Three treatments: control (CTR), supplementation with 32 mg/kg DM sodium monensin (MON, positive control), and supplementation with 2.8 g/kg DM of PE were tested. Animals were weighed (303 ± 3.6 kg of initial BW) and randomly distributed by BW in six pens. Concentrate and straw were both offered ad libitum. Animal body weight (BW), and group concentrate and straw consumptions were recorded every 3 weeks until the first animals reached the target slaughter weight of 460 ± 30 kg. Rumenocentesis was performed to all bulls at 63 days of study at 09:00 h to determine rumen pH, ammonia nitrogen, and volatile fatty acid concentrations. Blood samples from all bulls were taken at 7, 35, and 71 days of study at 09:00 h to determine cortisol, glucose, insulin, and leptin concentrations. At 84 days of study, when the first bulls reached the target BW, CTR bulls had lower (P<0.001) BW (428.1 ± 1.10 kg) than bulls supplemented with MON (435.6 ± 1.10 kg), however, the BW of PE supplemented bulls (432.6 ± 1.10 kg) did not differ from CTR or MON supplemented bulls. Neither monensin nor PE supplementation affected feed consumption, or feed efficiency. Rumen pH was lower (P<0.001) in MON and PE treatments than in CTR. Rumen molar concentrations of propionic acid increased (P<0.05) in MON and PE bulls compared to CTR bulls. Bulls supplemented with PE had greater (P<0.05) serum insulin concentration than MON or CTR bulls. Cortisol serum concentration remained unchanged in the CRT treatment with time, in contrast to MON and PE treatments that elicited a decrease in cortisol serum concentration between 7 and 35 days of study and an increase thereafter. Leptin serum concentration increased (P<0.01) from 35 to 71 days of study; however, in MON bulls this increase was not as pronounced as in PE and CTR bulls. In bulls fed high-concentrate diets, plant extract supplementation had similar effects on growth, rumen fermentation, and cortisol serum concentration to monensin supplementation.