THE ROLE OF FEED CONSUMPTION AND FEED-EFFICIENCY IN COPPER-STIMULATEDGROWTH

Two experiments were conducted to study the role of feed intake and fe ed efficiency in Cu-stimulated growth of weanling pigs. In Exp. 1, 42 pigs were randomly assigned into three treatments: 1) control: ad libi tum 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 g reater (P <.05) ADG and ADFI than the control pigs. The pair-fed/Cu gr oup had an intermediate ADG. Gain:feed (GF) was not significantly affe cted 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 mitogeni c activity and growth hormone mRNA concentrations for both feeding met hods. 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 sulfat e vs Cu lysine) was used in a 24-d experiment involving 96 pigs. Feedi ng copper increased(P <.05) ADG and GF. The magnitude of the Cu-stimul ated growth was reduced by restricted feeding (Cu level x feeding leve l 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 fr om Cu lysine was reduced by restricted feeding (Cu source x feeding le vel interaction, P <.05). High dietary Cu stimulated (P <.05) serum mi togenic activity; the stimulation was greater for Cu lysine than for C u sulfate. Feeding Cu numerically increased GH mRNA concentration. Res tricted feeding reduced overall serum mitogenic activity (P <.05); but the response to high dietary Cu and Cu lysine was still evident. In s ummary, Cu-stimulated growth was largely dependent on a simultaneous i ncrease in feed intake, but there were some improvements in GF. The in fluence of Cu on serum mitogenic activity was independent of feed inta ke or growth in both experiments, which indicates a direct action of C u on the growth regulatory system.