عنوان مقاله [English]
Background and objectives: Zinc has a role in many cases such as rumen microbial activity, immunity, and blood metabolites. But, there is no sufficient information on the effect of nano and organic Zn supplements on microbial protein synthesis and immunity variables in Holstein calves. Thus, this study was conducted to assess the effect of using nano-ZnO and Zn-methionine instead of ZnO (equal to or twice NRC 2001-recommended level) on urinary purine derivatives, microbial protein, immunoglobulins and nitrogenous compounds of the blood in pre- and post-weaning calves.
Materials and methods: Sixty suckling Holstein calves were assigned into one of the 6 experimental groups (10 replications) in a completely randomized design. The experimental treatments were the diets containing: 1- ZnO equal to NRC recommendation, 2- Zn-methionine equal to NRC recommendation, 3- nano-ZnO equal to NRC recommendation, 4- ZnO twice NRC recommendation, 5- Zn-methionine twice NRC recommendation, and 6- nano-ZnO twice NRC recommendation. During 7 to 30 days of age, the calves were fed with milk and starter concentrate according to the above treatments. From days 31 to 70, milk and mixed alfalfa-starter (at the ratio of 10:90) were provided for the calves. Weaning was done at 70 days of age and during post-weaning period (71 to 100 days of age), the calves were freely fed with experimental diets (alfalfa and starter concentrate at the ratio of 20:80). During pre- and post-weaning periods, the urinary purine derivatives, microbial N synthesis, total globulin, IgM, IgG, total protein, albumin, urea-N, creatinine and glucose of the blood were determined. Data were analyzed in a factorial experiment (3×2) using PROC MIXED of SAS (2001).
Results: Urinary purine derivatives and microbial N synthesis were not affected by replacing ZnO with nano-ZnO and Zn-methionine during pre- and post-weaning periods. Zinc chemical form had no significant effect on the blood concentrations of total globulin, IgM and IgA. Total protein, albumin, urea-N, creatinine and glucose in the blood of the calves fed with inorganic, nano or organic Zn supplements were the same. Moreover, increasing Zn level in the diet had no effect on urinary purine derivatives, microbial N synthesis, total globulin, IgM, IgA, total protein, urea-N, creatinine and glucose.
Conclusion: Using nano-ZnO and Zn-methionine instead of ZnO and also the increasing dietary Zn level had no effect on microbial protein synthesis, IgM, IgA, nitrogenous compounds and glucose in the blood of the calves. Thus, feeding the conventional inorganic Zn source (ZnO) at the NRC-recommended level was sufficient to supply the calves’ requirement during pre- and post-weaning periods and the other sources are not recommended.