The effects of copper supplements on the performance up to 45 lb. live weight of early weaned pigs were measured in two experiments. Copper sulphate included as 0·1% of the diet had no apparent adverse effect on the piglets, even when it was introduced immediately after weaning at about 8 lb. live weight, but improved rate of gain by 6 and 12% and feed conversion efficiency by 5 and 6% in the two experiments, respectively. The length of the period of slow growth after weaning was reduced in both experiments. There was no clear advantage in delaying the introduction of the high-copper diet until the pigs weighed 17 or 26 lb.

The second experiment was a 2 x 2 factorial, the second factor being the presence or absence in the diet of antibiotic (present throughout in the first experiment). Antibiotic appeared to have slight beneficial effects on growth rate and feed conversion, which were additive to the effects of copper so that the best results were obtained from the diet containing both copper and antibiotic.

In a continuation of the first experiment it was found that the early copper treatment had no effect on rates of gain and feed conversion between 55 and 200 lb. live weight or on carcass measurements. The inclusion of a copper supplement in the diet from 55 to 200 lb. improved feed conversion by 4% and rate of gain by 3·5%, reduced the thickness of streak and increased the ratio of width to depth of eye muscle. None of these responses was affected by the copper treatment prior to 55 lb. live weight.