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(R), 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 +/- 13.6 kg of initial B W) and randomly distributed by B W 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) B W (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. (C) 2006 Elsevier B.V. All rights reserved.