Effects Of Zinc Sources On Rumen Fermentation And Digestibility-Metabolism Of Diet Nutrients In Steers

Three Simmexte crossbred steers (600+100 kg body weight) fitted with permanent ruminal cannulas were used in a 3X3 Latin squre design to investigate the effect of different zinc sources on rumen fermentation and digestibility-metabolism of nutrients.The basal diet consisted of corn grain,cottonseed meal,straw,and alfalfa with a forge: concentrate ratio of about 1: 1 (air-dry basis) .Treatments consisted of: 1) control (no supplemental Zn); 2) ZnSO4 (60 mgZn/kgDM from Zn Sulfate); 3) Zn-Met (60 mgZn/kgDM from Zn methionine) .The experiment included 3 feeding periods of 15 days each,and each period comprised a 9-day adaptation and 6-day data collection.In the first two days of data collection, ruminal fluid pH, NH3-N,VFA,and Zn were determined; In the middle of three days of data collection, disappearence rate of DM, OM, CP, NDF, ADF, and Zn were measured in addition to retention rate of N and Zn were also determined; The last day blood were obtained for serum Zn and alkaline phosphatase. The results showed that:There were no signiffcant effect of zinc sources on ruminal pH(P>0.05).Dynamic changes of ruminal fluid pH were more steady in treatments control and ZnSO4 than of Zn-Met.Compared with the control, the mean NHs-N concentration in treatment ZnSO4 and Zn-Met reduced 14.04 %, 18.77 %(P>0.05),repectively. There were signiffcant effect of the mean NHs-N concentration in treatment Zn-Met in a feeding period and NHs-N concentration at 4 hours after feeding compared with control. Zn-Met could decreased ruminal NHs-N concentration of steers.There were no significant effect of zinc sources on ruminal VFA concentration(.P>0.05) .In a feeding period ,the mean concentration in treatment ZnSO4 of acetate, propionate, butyrate and total VFA increased by 1.46 %,2.22 %,0.62 %,and 1.52 %,respectively, compared with the control.but treatment Zn-Met decreased by 1.46 %,19.89 %,0.10 %,0.02 %,respectively. The ratio of acetate to propionate concentration at different times and mong treatments were not different (P>0.05).There were no significant effect of zinc sources on ruminal fluid zinc(P>0.05). The mean ruminal fluid zinc in treatment ZnSO4 reduced a little compared the control,but Zn-Met increased by 3.82 %.There were no significant effect of zinc sources on disappearence rate of diet nutrients CP>0.05). The disappearence rate in treatment ZnSO4 of DM, OM, CP, NDF, ADF in diets reduced to 2.45 %,2.20 %,1.64 %,2.06 %,4.04 %,respectively, compared with the control, Zn-Met also declined 1.38 %,1.16 %,0.87 %,0.63 %,1.92 %. The disappearence rate in treatment Zn-Met of zinc increased by 5.03 % than of ZnSO4.The retention rate of diet nitron differed among treatments (P>0.05).Compared with the control, the retention rate in treatment ZnSO4 and Zn-Met increased by 2.91 %,12.11 %,repectively.The retention rate of diet zinc also had a increaseing tendency.Supplied Zn-Met could improved Zn and Nitron retention in steers.The blood parameter were not affected by different treatments(.P>0.05).The serum zinc concentration and activity of alkaline phosphatase in treatment ZnSO4 increased by 6.52 %,8.99 %,compared with the control,respectively, but Zn-Met depressed by 4.81 %,3.08 %.