Increasing levels of Chlorella spp. on in vitro fermentation and methane production in a corn silage-base diet

26 Background: Generally, forages used in cow-calf and backgrounding operations have low 27 crude protein and high fiber concentration, limiting animal performance and increasing 28 greenhouse gas emissions. Chlorella spp., a green micro-algae, shows promising attributes 29 to provide nutrients, especially nitrogen, in low-protein diets. However, information is 30 limited regarding the effects of Chlorella spp. on in vitro fermentation and methane (CH 4 ) 31 production. Objective: To evaluate the effects of increasing inclusion levels of algae 32 ( Chlorella spp.) on ruminal in vitro fermentation profile and CH 4 production in a corn silage-33 based diet. Methods: Incubations were conducted on three separate days using corn silage 34 and gin trash as substrate (70:30 ratio, respectively). Treatments were control (without algae), 35 and 1, 5, and 10% of algae inclusion in the substrate replacing basal diet. Ruminal fluid was 36 collected from two ruminally cannulated Angus crossbred steers fed ad libitum a corn silage 37 and gin trash diet. The final pH, the concentration of volatile fatty acids (VFA) and ammonia 38 nitrogen (NH 3 -N), in vitro organic matter digestibility (IVOMD), total gas, and CH 4 39 production were determined after 24 h of incubation. Variables were evaluated using the 40 MIXED procedure of software SAS, and means were compared using orthogonal polynomial 41 contrast. Results: Algae inclusion linearly increased (p<0.01) the IVOMD. However, the 42 final pH and concentration of VFA and NH 3 -N were not different (p>0.05) among the algae 43 levels. The molar proportion of VFA and the acetate:propionate ratio were not affected 44 (p>0.05) by increasing algae inclusion. Finally, total gas and CH 4 production were not 45 different (p>0.05) among treatments. Conclusions: The inclusion of Chlorella spp. did not