Effect of elevated cobalt intake on fermentative parameters and protozoan population in RUSITEC

The effects of 2, 4 and 8 mg cobalt per kg dry matter (DM) of feed ration consisting of 11.5 g hay, 2.8 g barley and 1.6 g molasses (10% of the DM feeding ration) were examined in an artificial rumen simulation technique (RUSITEC) as affecting fermentation and protozoan population. The cobalt content of the feed ration was 0.2 mg kg−1 DM (control value). The 2, 4 and 8 mg kg−1 DM intake level of cobalt was achieved by CoSO4 supplementation. The results of the experiment showed no changes in the degradability of DM, organic matter, neutral detergent fiber, acid detergent fiber, production of total gas and methane. The cobalt level of 8 mg kg−1 DM significantly increased the degradability of cellulose by approximately 10% as contrasted to 0.2 mg level. Total production and molar proportion of volatile fatty acids were not significantly affected by increased cobalt intake except for an increased molar proportion of iso-butyric acid at 4 mg cobalt intake. Other parameters of rumen fermentation — glucose utilization, adenosine-triphosphate production, fermented hexose, fermented organic matter, hydrogen recovery and nitrogen utilization — were not influenced by the higher level of cobalt intake. Major ciliate groups in RUSITEC were Entodinium spp. and Dasytricha ruminantium. Minor groups were Isotricha spp., Ophryoscolex caudatus tricoronatus, Polyplastron multivesiculatum, Enoploplastron triloricatum, and Diploplastron affine. A cobalt level of 8 mg significantly decreased the total number of rumen ciliates, but only the number of Isotricha spp. was significantly decreased at all cobalt levels examined. The cobalt accumulation in the protozoan and bacterial fractions of the two vessels were measured. At the cobalt intake level of 0.2 mg kg−1 DM of feed the 24 and 33% of the Co was recovered in the protozoan and bacterial fraction, respectively, after a 12-day operation of RUSITEC. At the cobalt intake level of 2 mg, the values for the protozoan and bacterial fractions were 49 and 51%, respectively.