The role of feed consumption and feed efficiency in copper-stimulated growth.

Two experiments were conducted to study the role of feed intake and feed efficiency in Cu-stimulated growth of weanling pigs. In Exp. 1, 42 pigs were randomly assigned into three treatments: 1) control: ad libitum access to a corn-soybean meal-dried whey basal diet; 2) ad libitum/Cu: ad libitum access to the basal diet supplemented with 215 ppm of Cu; or 3) pair-fed/Cu: pair-fed the Cu-supplemented diet to the level of the control. Over the 14-d experiment, the ad libitum/Cu pigs had greater (P < .05) ADG and ADFI than the control pigs. The pair-fed/Cu group had an intermediate ADG. Gain:feed (GF) was not significantly affected by treatments but tended to be improved in the pair-fed/Cu pigs. Feeding copper increased (P < .05) the concentration of Cu in the serum, liver, and brain. Also, feeding Cu increased (P < .05) serum mitogenic activity and growth hormone mRNA concentrations for both feeding methods. In Exp. 2, a 2 x 2 x 2 factorial arrangement of treatments with two levels of Cu (15 vs 200 ppm), two levels of feeding (ad libitum vs restricted [85% of the ad libitum]), and two sources of Cu (Cu sulfate vs Cu lysine) was used in a 24-d experiment involving 96 pigs. Feeding copper increased (P < .05) ADG and GF. The magnitude of the Cu-stimulated growth was reduced by restricted feeding (Cu level x feeding level interaction; P < .05). The ADFI was greater (P < .05) for the pigs fed high dietary Cu only during d 1 to 6. Pigs fed Cu lysine had greater ADG and ADFI than those fed Cu sulfate (P < .05); the benefit in ADG from Cu lysine was reduced by restricted feeding (Cu source x feeding level interaction, P < .05). High dietary Cu stimulated (P < .05) serum mitogenic activity; the stimulation was greater for Cu lysine than for Cu sulfate. Feeding Cu numerically increased GH mRNA concentration. Restricted feeding reduced overall serum mitogenic activity (P < .05), but the response to high dietary Cu and Cu lysine was still evident. In summary, Cu-stimulated growth was largely dependent on a simultaneous increase in feed intake, but there were some improvements in GF. The influence of Cu on serum mitogenic activity was independent of feed intake or growth in both experiments, which indicates a direct action of Cu on the growth regulatory system.