Effects Of Cobalt And Folic Acid Supplementation On Growth Performance,nutrient Digestion And Ruminal Fermentation In Dairy Calves

This study investigated the effects of cobalt(Co)and folic acid(FA)on growth performance,nutrient digestion,rumen fermentation and blood metabolites in Holstein dairy calves.Sixteen Chinese Holstein dairy calves with 86.2 ± 10 days of age and 83.07 ± 13.07 kg of body weight were assigned to one of four groups in a 2 × 2 factor and randomized block design.Cobalt sulfate at the level of 0 or 0.1 mg Co/kg dry matter(DM)was supplemented to diets without or with 7.2 mg FA/kg DM addition.Addition of Co did not affect dry matter intake(DMI)but increased average daily gain(ADG)and reduced feed conversion ratio(FCR).Supplementation with FA increased DMI and ADG.Digestibility of DM,organic matter(OM),crude protein(CP),neutral detergent fiber(NDF)and acid detergent fiber(ADF)in the total-tract increased with Co or FA addition.Supplementation with Co or FA increased N retained and the ratio of N retained to digestible N.Supplementation of Co increased rumen total volatile fatty acids(TVFA)concentration,propionate proportion but reduced acetate proportion,acetate to propionate ratio and ammonia nitrogen concentration.Addition of FA increased rumen TVFA concentration and ruduced ammonia nitrogen concentration.Cellobiase activity increased with Co supplementation.addition of Co increased populations of total protozoa R.albus,F.succinogenes,B.fibrisolvens and Rb.amylophilus but reduced total methanogens population.Supplementation with FA increased populations of R.albus,B.fibrisolvens and Rb.amylophilus but reduced population of total methanogens.Supplementation of Co reduced serum urea nitrogen and addition of FA increased concentration of FA in serum.The results indicated that supplementation of Co or FA improved growth performance and rumen fermentation,but significant FA × Co interaction was not observed during the trial.