ABSTRACT
Two 47-d experiments were conducted with 21-d-old weaned pigs (PIC 1050, initially 6.1 kg) to determine the effects of feeding low or high doses of chlortetracycline (CTC) and antibiotic alternatives (Cu, Zn, and essential oil [EO]), alone or in combination, on growth performance. On d 5 postweaning, pens of 5 pigs were allotted to diet treatments with 8 (exp. 1) or 7 (exp. 2) replicate pens per treatment. In exp. 1, treatments were fed from d 5 to 26 postweaning and arranged in a 2 × 3 factorial with main effects of added ZnO (0 vs. 2,500 ppm of Zn) and CTC (0, 55, or 441 ppm). In exp. 2, treatments were fed from d 5 to 33 and structured in a (2 × 2 × 2) + 2 factorial with main effects of added CuSO4 (0 vs. 125 ppm Cu), added ZnO (0 vs. 3,000 ppm Zn from d 5 to 12 and 2,000 ppm Zn from d 12 to 33), and Regano EX (0 vs. 0.1% Regano EX containing 5% Origanum oil). The 2 additional treatments were subtherapeutic (55 ppm) and therapeutic (441 ppm) levels of CTC. Following the treatment period, a common diet without antimicrobial was fed until d 47. All diets contained 16.5 ppm Cu and 110 ppm Zn from the trace mineral premix. In exp. 1, no ZnO × CTC interactions were observed. Feeding ZnO increased (P < 0.05) ADG, ADFI, and BW during the treatment period and increased (P < 0.05) ADG and ADFI overall (d 5 to 47). Pigs fed CTC had increased (linear, P < 0.05) ADG, ADFI, and BW during the treatment period and had marginally significant increases (linear, P < 0.10) in overall ADG and ADFI, but overall G:F tended (quadratic, P = 0.070) to increase then decrease as CTC increased. During the treatment period in exp. 2, EO did not affect ADG or ADFI, whereas pharmacological levels of Cu, Zn, and CTC increased (P < 0.05) ADG with coinciding increases (P = 0.055, 0.006, and linear 0.079, respectively) in ADFI. Copper, Zn, and CTC did not affect G:F. EO decreased (P = 0.009) G:F. Diet treatments had minimal carryover effects on subsequent nursery pig growth performance. Overall from d 5 to 47, Cu increased (P = 0.018) ADG, Zn increased (P < 0.05) ADG and ADFI, and EO tended to decrease (P = 0.086) G:F. In conclusion, increased dietary Cu, Zn, or CTC improved weanling pig performance while EO elicited no growth benefits. The benefits of added Zn from ZnO and CTC were additive and could be included together in diets to maximize growth performance of weaned pigs.
ABSTRACT
A total of 480 pigs (PIC 327 × 1050; initially 48.7 ± 2.3 kg) were used to determine the interactive effects of supplemental Cu, Zn, and ractopamine HCl (RAC) on finishing pig growth performance, carcass characteristics, and antimicrobial susceptibility of enteric bacteria. Treatments were arranged in a 2 × 2 × 2 factorial with the main effects of added Cu (CuSO; 0 vs. 125 mg/kg Cu), Zn (ZnO; 0 vs. 150 mg/kg Zn), and RAC (0 vs. 10 mg/kg during the last 28 d prior to marketing). All diets contained 11 mg/kg Cu and 73 mg/kg Zn from the trace mineral premix. Pens of pigs were balanced and blocked on initial BW and then randomly allotted to 1 of the 4 mineral treatment diets. At 28 d prior to marketing, pens within each block and mineral treatment were randomly assigned to receive either 0 or 10 mg/kg RAC in addition to the mineral treatment. Adding either Cu or Zn alone did not improve ADG or ADFI yet resulted in numerical improvements in overall G:F and caloric efficiencies, but improvements were not additive (Cu × Zn, = 0.057, = 0.068, and = 0.064 for G:F and caloric efficiency on a ME and NE basis, respectively). Ractopamine improved ( < 0.001) overall ADG, G:F, and caloric efficiency, thereby increasing final BW by 3% with no change in ADFI. Ractopamine also increased ( < 0.001) HCW, percentage carcass yield, G:F, loin depth, and percent fat-free lean and decreased ( = 0.014) backfat. Adding Zn or Cu alone to diets containing RAC numerically improved percent yield and HCW G:F, but this effect was absent when the Cu or Zn was added to the control diet or when Cu and Zn were fed in combination in RAC diets (Cu × Zn × RAC, = 0.011 and = 0.018 for yield and HCW G:F, respectively). Fecal samples were collected on d 0 and at the conclusion of the finishing period (d 90) for bacterial isolation and antimicrobial susceptibility determinations according to Clinical and Laboratory Standards Institute minimal inhibitory concentrations breakpoints. spp. and isolates displayed varying levels of resistance to certain antibiotics prior to initiation of treatments on d 0. Resistance to most antibiotics decreased ( < 0.05) over time or was stable for those that had a low baseline percentage of resistance. Neither Zn nor RAC adversely affected antimicrobial resistance. However, extended feeding of 125 mg/kg Cu throughout the finishing period seems to decrease enterococcal susceptability to tetracycline, tylosin, and quinupristin/dalfopristin.
