Effects of copper, with and without ferrous sulfide, and antibiotics on the performance of pigs.

Three trials were conducted with 252 pigs to determine the effects of the dietary additions of Cu (250 ppm as copper sulfate), with and without sulfide (500 ppm as ferrous sulfide), and antibiotics (55 ppm chlortetracycline or 27.5 ppm virginiamycin) on the performance and liver Cu stores of growing-finishing pigs. Single additions of Cu, chlortetracycline or virginiamycin to a 16% protein, corn-soybean meal-based diet improved daily gains by 4.0, 4.2 and 3.4% and feed to gain ratios by .3, 2.9, and 1.3%, respectively, in comparison with those of pigs fed the control diet. The addition of ferrous sulfide to the high Cu diets reduced liver Cu stores from 278 to 21 ppm, a level approaching that of the control pigs, and increased the growth response to supplemental Cu by 4.0%. The inclusion of both Cu and an antibiotic in the diet in the in the absence or presence of sulfide resulted in daily gains in feed to gain ratios similar to those of pigs receiving a single antimicrobial agent. These data suggest that the growth-promoting effects of Cu and chlortetracycline or Cu and virginiamycin are not additive in the growing-finishing pig allowed to consume feed ad libitum.