A Study On Copper, Zinc, Cobalt, Iron And Iodine Requirements Of Lactating Holstein Cows

One in vritro fermentation experiment and one mineral balance trial using lactating dairy cows were conducted to examine copper, zinc, cobalt, iron and iodine requirements of Holstein cows during lactating period.Using in vitro gas production method, Expt.l was conducted to investigate the effeccts of supplemental copper, zinc, cobalt, iron, and iodine on ruminal fermentation by washed suspension of rumen microorganisms. A purified diet consisting of crystalline cellulose, soluble starch, glucose, and trypsin was incubated with five different concentrations of these minerals. In vitro digestibility of nutrients after 24h incubation and gas production during 72h incubation were measured. The cobalt level of 0.3 mg/kg sinificantly (P<0.05) increased the digestibility of cellulose as compared with other cobalt levels. Compared with control, addition of copper significantly (P<0.05) increased the potential gas production, rate of gas production and maximum gas production, whereas there was no significant (P>0.05) difference between the addition levels. The treatment for zinc addition at 40 mg/kg and for iron addition at 60 mg/kg had higher rate of gas production (P<0.05) than the treatments added 20 mg Zn/kg and 15 mg Fe/kg respectively. Cobalt addition at a concentration of 0.4 mg/kg had sifnificantly higher (P<0.05, L=0.004) molar proportion of valerate than the control with no cobalt addition, whereas there were no significant differences (P>0.05) between other addition treatments. The addition of copper, zinc, iron and iodine did not alter the concentration of NH3-N, pH, total VFA production and individual VFA profile (P>0.05).An orthogonal design was used with sixteen lactating cows and sixteen diets to evaluate the requirement of copper, zinc, cobalt, iron and iodine. The trial consisted of 14 days for adaption and 7 days for sampling. During sampling period, feed intake and output of feces, urine and milk were daily recorded. The maintenance requirement of copper, zinc, iodine were 9.8 ug/kg BW, 43.1 ug/kg BW and 3.6 ug/kg BW respectively, and the contents of copper, zinc and iodine in the milk were measured to be 0.19 mg/kg, 3.7 mg/kg and 28 ug/kg, respectively. Because cobalt and iron contents in the trial diets much exceeded the requiremnt of lactating cows, their requirements for maintenance were not examined from this trial. The digestibility of DM, NDF, CP and OM was unaffected (P>0.05) by addition of copper, zinc, cobalt, iron and iodine. Addition of copper did not change copper concentration, ceruloplasmin activity in serum (P>0.05), while addition of zinc in the diet resulted in an increased zinc concentrations in serum. T3 and T4 concentrations were little affected by iodine addition level (P>0.05).