Effects of supplementation of organic and inorganic combinations of copper, cobalt, manganese, and zinc above nutrient requirement levels on postpartum two-year-old cows.
The objective of this study was to determine whether a combination of Cu, Co, Mn, and Zn in an organic or inorganic form fed at higher than nutrient recommendations for 2-yr-old cows from calving to breeding would affect pregnancy rate, calving date, calf performance, and cow liver and serum mineral concentrations. Crossbred 2-yr-old cows were used after calving in 1994 (n = 127) and 1995 (n = 109). Cows were blocked by calving date to one of three treatments: 1) no supplemental minerals (CTL), 2) organic minerals (ORG), or 3) inorganic minerals (ING). Minerals were fed for the same daily intake for both organic and inorganic treatments: Cu (125 mg), Co (25 mg), Mn (200 mg), and Zn (360 mg). Cows were individually fed a mineral-protein supplement with grass hay from calving (February-March) to before breeding (May 15). Hay intakes were calculated using chromium oxide boluses to determine fecal output. Fecal excretion of minerals was calculated following trace element analysis of feces. Liver biopsies were obtained before calving, after calving (start of supplementation), at the end of supplementation, and in midsummer. Over 2 yr, more cows did not become pregnant (P < .01) in ORG (11/78) and ING (11/78) treatments than in CTL (0/80) treatments. A treatment × year interaction was found for day of conception. Cows in the ORG group conceived later (P < .01) than cows in the ING or CTL groups in 1994. In 1995, there was no difference (P > .10) in day of conception among groups. Liver Zn and Mn concentrations were not different (P > .10) and Cu concentrations increased (P < .01) for the ORG and ING groups. Cows in the ORG and ING groups had higher (P < .01) concentrations of Cu, Mn, and Zn in the feces than the CTL cows. Trace elements in the feces did not differ for ORG and ING groups. Results indicate that combinations of Cu, Co, Mn, and Zn fed at higher levels than are required reduced reproductive performance.