STIMULATION OF GROWTH BY INTRAVENOUS-INJECTION OF COPPER IN WEANLING PIGS

This study was conducted to examine whether Cu could exert its growth- promoting effect when injected, rather than being fed, and thus bypass the gastrointestinal tract. In two 18-d experiments, pigs were inject ed every 2 d with a Cu histidinate or histidine solution. Amounts of C u injected were calculated to simulate varying absorption rates in pig s fed 250 ppm of dietary Cu. In Exp. 1, 44 pigs were randomly assigned to four groups of 11 pigs each. Pigs were injected with four levels o f Cu histidinate (0, 5, 10, and 15% estimated apparent absorption coef ficients based on calculated feed intake). Average daily gain responde d quadratically (P <.05) to levels of Cu histidinate; maximum growth w as seen in the 5% group. At d 6, serum mitogenic activity also exhibit ed a similar quadratic response (P <.05). In Exp. 2, estimated Cu abso rptions of 0, 2, 4, 6, and 8% were tested. Forty-five pigs were random ly assigned to five groups of nine pigs each and injected as in Exp. 1 . Both ADG and serum mitogenic activity displayed a quadratic response (P <.05); the maximum response was seen in the 4% group. Liver Cu con tent, superoxide dismutase activity, and serum Cu concentrations were linearly increased (P <.05) with increasing dosage of Cu in both Exp. 1 and 2. Also, brain Cu content linearly increased (P <.05) with incre asing dosage of Cu in Exp. 1 and 2. Pituitary growth hormone mRNA conc entrations in Exp. 2 were not significantly influenced by treatments. This study shows that Cu may stimulate growth when injected intravenou sly, thus bypassing the gastrointestinal tract. Therefore, a mode of a ction that does not involve antimicrobial activity should be considere d.