Effects Of CoCO₃ On Performances,Rumen Fermentation And Serum Biochemical Parameters Of Lactating Dairy Cows

This experiment was to determine the effects of different cobalt carbonate(CoCO3)supplement levels on rumen fermentation,productivity and serum biochemical parameters of lactating dairy cows.Thirty-six lactating Holstein dairy cows with similar body condition,parity,lactation stage and milk yield were blocked and randomly divided into 6 supplementationlevels of CoCO3[0(control group),6(0.5 times),12(recommended dose group),30(2.5times),60(5 times),120(10 times)mg of the diets(on DM basis)].The experiment was continued up 56 d,including 14 d of adaptation period and 42 d of experiment period.The test results were showed as follows:1.Effects of different supplementation levels of dietary CoCO3 on production performance and nutrition digestibility of lactating dairy cows.The results showed that:(1)There was no significant effect on feed.intake of lactating dairy cows by different supplementation levels of CoCO3(P>0.10);The milk yield of 60 mg group showed a downward trend.(2)There was no significant effect on the milk fat percentage,milk total solids percentage and milk urea nitrogen percentage(P>0.05);On the 14th day and the 28th day,the milk protein and milk lactose percentage of 30 mg group were significantly higher than the control group(P<0.05),the milk lactose percentage and milk protein percentage of 60 mg group were both decreased,and the milk lactose percentage of 60 mg group were significantly lower than the other treatment groups on the 42th day(P<0.05).(3)On the 14-42th days,there was no significant effect on milk vitamin B12 concentration of lactating dairy cows by different supplementation levels of CoCO3(P>0.10).(4)The apparent digestibility of EE and NDF was no difference between control and treatment groups(P>0.10);The apparent digestibility of CP and ADF in 30 mg group was significantly higher than that in control group(P<0.05),and the apparent digestibility of ADF in 30 mg was significantly higher than the other treatment groups(P<0.05).2.Effects of different supplementation levels of dietary CoCO3 on rumen parameters and rumen bacterial abundance of lactating dairy cows.The results showed that:(1)There was no significant effect on rumen fluid pH value,ammonia nitrogen(NH3-N)and total volatile fatty acid(TVFA)by different supplementation levels of CoCO3(P>0.10);Propionate concentration was significantly higher than the control group(P<0.05);Microbial protein(MCP)concentration increased with the addition of CoCO3,30 mg and 60 mg group was significantly higher than the control group(P<0.05).(2)The concentration of rumen fluid vitamin B12 in 12～60 mg group was significantly higher than the control group and 6 mg group(P<0.05).(3)The addition of different levels of cobalt carbonate in diets had no significant effect on the Chao1,ACE and Shannon index of rumen fluid in lactating dairy cows(P>0.10);Bacteroidetes,Proteobacteria,and Firmicutes were the predominant bacterial groups at the level of the phylum;Prevotella and Succinivibrionaceae were the predominant at the level of genus.3.Effects of different supplementation levels of dietary CoCO3 on serum biochemical indexes of lactating dairy cows.The results showed that:(1)There was no significant effect on the concentration of serum GGT by different supplementation levels of CoCO3(P>0.10);The concentration of serum ALT decreased gradually in 6 mg and 30 mg group,the concentration of serum AST and serum LDH increased gradually,and the concentration of serum ALP first increased then stabilized.(2)There was no significant effect on the concentration of serum TP,serum ALB,serum GLO,serum CREA,serum BUN,serum UA and the ratio of serum ALB to GLO of lactating dairy cows by different supplementation levels of CoCO3(P>0.10).(3)There was no significant effect on the concentration of serum CHO,serum HDL,serum LDL and serum NEFA of lactating dairy cows by different supplementation levels of CoCO3(P>0.10),however the concentration of NEFA of each group increased gradually on the 14～42th days,the maximum value was 1046.18 μmol/L;The concentration of serum GLU in 6～60 mg group increased gradually,the concentration of serum GLU in 30 mg group was significantly higher than the control group and 60mg group(P<0.05);The concentration of serum TG in 6-60 mg group first increased then stabilized.(4)There was no significant effect on the concentration of serum IgG and IgA of lactating cows by different supplementation levels of CoCO3(P>0.10);The IgM concentration of 6～30 mg group increased gradually on the 14-42th days,however,the IgM concentration of 60 mg group decreased gradually to the lowest value of 90.87 μg/mL;The IgM concentration of 60 mg group was significantly higher than that of 6 mg and 12 mg group on the 14th day(P<0.05).(5)There was no significant effect on the concentration of serum MCV,MCH and MCHC of lactating cows by different supplementation levels of CoCO3(P>0.10).The concentration of RBC,HCT and HGB of each group decreased gradually on the 14-42th;The concentration of RBC,HCT and HGB in each treatment groups were significantly higher than those in the control group on the 42th day(P<0.05).(6)There was no significant effect on the concentration of serum vitamin B12 of lactating dairy cows by different supplementation levels of CoCO3(P>0.10).Conclusion:In conclusion,the experiment indicated that 30 mg CoCO3 supplementation in the diet is beneficial to improve the performance and nutrient absorption and health of dairy cows,however,the 60 mg CoCO3 supplementation in the diet is unfavorable to the performance.Therefore,it is suggested that the level of CoCO3 should be 30 mg and the safety factor should be 2.5 times,the maximum level of CoCO3 should be 60 mg.