Effect of Source and Level of Dietary Protein on Pigs Fed High-Copper Rations

Forty individually-fed pigs were given rations containing either casein or soybean meal as the source of supplemental protein. With each protein source rations were formulated to contain either 14 or 22% protein and 250 or 500 ppm of copper. Significant three- and two-factor interactions were found for gain, copper digestion, hemoglobin, hematocrit and liver and heart copper values. Daily gain and daily feed consumption were adversely affected when casein supplied the supplemental protein and when the rations contained 500 ppm of copper. Daily gain was also enhanced by the higher level (22%) of dietary protein. Apparent digestion coefficients for dry matter and ether extract were not influenced significantly by protein source, protein level or copper level. Protein digestibility was higher when casein was used and when the rations contained 22% protein. Hemoglobin levels were not influenced significantly by level of dietary protein, but were reduced when the rations contained casein or 500 ppm of copper. Hematocrit was affected only by copper level. Neither red nor white blood cell counts were influenced by protein source or by protein and copper level. The concentration of copper in the liver varied directly with weight gain; pigs fed rations containing soybean meal, 22% protein and 250 ppm of copper had the lowest liver copper values. Heart copper values with the exception of protein level exhibited a pattern similar to that obtained for liver copper.