Comparison of copper lysine and copper sulfate as copper sources for ruminants using in vitro methods.

Two in vitro experiments were conducted to estimate the availability of Cu from Cu Lys compared with Cu from CuSO4. In experiment 1, a 24-h ruminal fermentation (alpha-cellulose substrate) containing either .1% added S or 2% added urea was performed with 4, 12, or 96 ppm of added Cu as either Cu Lys or CuSO4. Soluble Cu was measured at the end of the 24-h incubation, and concentrations were higher for Cu Lys with added urea (1.16 vs. .45 ppm), but no differences existed between sources of added S. In Experiment 2, 20 ppm of Cu added as either Cu Lys or CuSO4 with and without the addition of 10 ppm of Mo and .75% S were used in an vitro study designed to simulate digesta passage through the ruminant. A 24-h ruminal fermentation (orchardgrass substrate) was followed by a 2-h digestion in pepsin and HCl (pH 2.3) and then a 2-h digestion in NaHCO3 and pancreatin (pH 6.6). Soluble Cu concentrations were analyzed after each step. Molybdenum and S addition decreased soluble Cu after ruminal fermentation and tended to decrease soluble Cu concentrations after digestion of pancreatin and NaHCO3. The source of Cu did not affect soluble Cu concentrations. Results suggest that Cu from Cu Lys and CuSO4 behave similarly in the digestive tract of ruminants.