A total of 350 weaned pigs (PIC 1050; initially 13.3 lb) were used in a 47-d study
to compare the effects of feeding antibiotic alternatives (copper, zinc, and essential
oils), alone or in combination, on nursery pig performance. Pigs were allotted to pens
at weaning (d 0) and fed a common starter diet with no antimicrobial for 5 d before
the start of the experiment. On d 5, pens of 5 pigs were allotted to 1 of 10 dietary
treatments in a randomized complete block design with 7 replications per treatment.
Dietary treatments were arranged in a 2 × 2 × 2 + 2 factorial with main effects of added
copper sulfate (CuSO4; 0 vs. 125 ppm Cu), added zinc oxide (ZnO; none 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. 45 g/ton
essential oils blend; Ralco Animal Nutrition, Marshall, MN). The 2 additional treatments
were growth-promoting and therapeutic levels of chlortetracycline (CTC at 50
or 400 g/ton). Pigs were fed experimental diets from d 5 to 33 followed by a common
corn-soybean meal–based diet without any antimicrobial, essential oils, or pharmacological
levels of Cu or Zn from d 33 to 47. To comply with FDA guidelines, CTC was
removed on d 19 from the diet of pigs fed 400 g/ton CTC, then added again from d
20 to 33. All diets contained 16.5 ppm Cu and 165 ppm of Zn from the trace mineral
premix. Essential oils had no effect on daily gain, but feeding CTC or pharmacological
levels of Cu or Zn improved the growth rate of nursery pigs. Carryover effects from any
of these dietary treatments on subsequent nursery growth performance were minimal.
Although there were no improvements in feed efficiency due to Cu or Zn, the inclusion
of an essential oils blend worsened feed and caloric efficiencies.
