Effects of feeding ensiled spearmint (Mentha spicata) byproduct on nutrient utilization and ruminal fermentation of steers

Two studies were conducted to determine the feeding value of ensiled spearmint byproduct (mint silage) for beef steers. Six ruminally fistulated steers were used in a completely randomized design to determine the effects of feeding mint silage or barley silage on ruminal fermentation and nutrient utilization. Ruminal nutrient degradbilities of mint silage relative to barley silage were determined in a randomized complete block design using two ruminally fistulated steers. Relative to barley silage, mint silage contained 17, 180, 20 and 330% more neutral detergent fiber (NDF), acid detergent lignin (ADL), crude protein (CP), and acid detergent insoluble protein, respectively. Steers fed mint silage consumed less (P<0.05) dry matter (DM) than those fed barley silage. Ruminal pH was higher (P<0.05) while concentrations of volatile fatty acids (VFA) were lower (P<0.05) for mint silage-fed steers than for barley silage-fed steers. Ruminal degradability of DM, CP and acid detergent fiber (ADF) was 46, 62 and 11% higher (P<0.05), respectively, for barley silage than for mint silage. Total tract digestibility of CP (290 versus 648 g kg−1), NDF (312 versus 471 g kg−1), ADF (300 versus 464 g kg−1), and gross energy (463 versus 654 J kJ−1) were lower (P<0.05) for steers fed mint silage than for those fed barley silage. Mint silage had a lower (P<0.05) digestible energy content (7.79 MJ kg−1) than barley silage (11.01 MJ kg−1). It was concluded that mint silage was poorly utilized by steers largely because of its high ADL and acid detergent insoluble protein contents.