1754
Effects of Beta-Extract of Humulus lupulus (hops) on Fermentation by Rumen Microbes in Continuous Culture
Beta-acids in hops (Humulus lupulus) have been shown to exhibit selective bacteriostatic properties toward Gram-positive and hyper-ammonia producing bacteria in pure and co-culture. Previous work with whole or ground hops in batch culture fermentations with rumen microbes demonstrated promising results toward altering microbial output, however confounding factors such as additional fermentable substrate and presence of condensed tannins in hops can be difficult to control. Use of hop beta-acid extract can eliminate major confounding factors and improve consistency of administration. The objective of this experiment was to evaluate effects of beta-acid extract from hops on microbial fermentation in continuous culture. Eight dual-flow continuous culture fermenters were used in two consecutive 10-d periods consisting of 7 d of adaptation followed by 3 d of sampling. A basal diet containing 44% corn silage, 14% alfalfa hay, 13% ground corn, 11% protein mix, 10% corn gluten feed, 5% cottonseed, and 3% liquid vitamin and mineral supplement on a DM basis was provided to the fermenters at a rate of 75 g of DM/L of fermenter volume/d. Hop beta-extract (BE) was added daily to the artificial saliva to supply 0, 600, 1200, or 1800 mg of β-acids/kg of diet DM/day. Effluents from sampling days were composited by fermenter within period, resulting in 4 reps/treatment. Beta extract inclusion had no effects on DM, OM or fiber digestion (P > 0.05). Volatile fatty acid production and N metabolism were not affected by BE inclusion (P > 0.05). Mean and maximum fermentation pH tended (P = 0.09) to increase linearly with increasing levels of BE inclusion. Time spent above pH 6.2 tended to increase linearly with greater BE inclusion (P = 0.08), while time spent between pH 5.8 and 6.2 tended to decrease linearly (P = 0.07). Changes in pH were less than biologically relevant levels. Increasing concentration of BE had very limited effects on fermentation measurements by rumen microbes using continuous culture fermenters.
Keywords:
continuous culture, hops, beta-acids, rumen