Effects of a specific blend of essential oil compounds on rumen fermentation

Effects of a specific preparation of essential oil compounds on rumen fermentation were determined using four mature sheep, each fitted with a permanent rumen cannula and receiving 110 mg per day of dietary essential oils compounds (EO; CRINA RUMINANTS, AKZO Nobel Surface Chemistry Ltd, Hertfordshire, UK). The basal ration comprised 1 kg DM per day of a 40:60 (DM) concentrate: forage mix fed in two equal meals. The forage was grass silage and the concentrate contained crushed barley grain, rapeseed meal, soyabean meal, molasses and a mineral and vitamin supplement (730, 125, 50, 80 and 15 g/kg fresh weight, respectively). Unsupplemented and EO-supplemented diets were fed in a 2 x 2 design with 6-week periods. EO inhibited ruminal degradation of soyabean meal N from dacron bags incubated in situ but not heat-treated rapeseed meal or hay. Deamination of amino acids measured in vitro in rumen fluid removed from the sheep decreased by 25% (P < 0.05). However, EO did not have a major influence on other aspects of rumen fermentation. Volatile fatty acid and ammonia concentrations were unaffected, and EO had no influence on proteolytic or peptidolytic activity of rumen fluid or on microbial protein production or protozoal numbers. Results suggest that EO alters protein degradation and amino acid deamination by inhibiting rumen microorganisms. (C) 2004 Elsevier B.V. All rights reserved.