Effects of Antibiotic Program and Floor Space in the Nursery and Grow-Finish Periods on Wean-to-Finish Growth Performance of Pigs Under Commercial Conditions

The effects of floor space and antibiotic program in both the nursery and grow-finish periods on wean-to-finish growth performance of pigs was evaluated using a RCBD with a 2 × 2 × 2 × 2 factorial arrangement of treatments: 1) Nursery floor space (0.31 vs 0.65 m²/pig); 2) Nursery antibiotic program (none vs antibiotics); 3) Grow-finish floor space (0.56 vs 0.65 m²/pig); 4) Grow-finish antibiotic program (none vs antibiotics). The antibiotic program included providing antibiotics in the feed (at growth promoting concentrations), in the water (to treat all animals on the specific study treatment for specific disease issues), and via injections (to treat individual animals for specific disease issues). The wean-to-finish study (from 6.4 ± 1.10 to 127.7 ± 2.28 kg BW) used a total of 3,840 pigs housed in single-sex pens of 30 (8 replicates). Pigs were given ad libitum access to feed and water throughout the study. The pen of pigs was the experimental unit; data were analyzed using PROC MIXED of SAS with the model accounting for the 4 treatments and all interactions, block, and replicate. Results reported are for the wean-to-finish period. There were no interactions (P > 0.05) between the floor space and antibiotic program treatments for any measure. Increasing floor space from 0.31 to 0.65 m²/pig in the nursery and from 0.56 to 0.65 m²/pig in grow-finish increased (P < 0.05) ADG (1.2 and 1.8% in nursery and grow-finish, respectively) and G:F (1.7 and 1.4%, respectively) with no effect (P > 0.05) on ADFI, or morbidity and mortality. Compared to the control (no antibiotics) providing antibiotics in nursery and grow-finish resulted in increased (P < 0.05) ADG (1.8 and 1.8%, respectively), ADFI (in nursery only; 2.7%), and G:F (grow-finish only; 2.9%). Morbidity and mortality for the overall study period were significantly increased when antibiotics were removed during the nursery period (7.6 vs. 12.3% for antibiotic and no antibiotic treatments, respectively; P < 0.001) and grow-finish period (8.5 vs. 11.4%, respectively; P < 0.01). The results of this study suggest that, regardless of floor space, the use of antibiotics significantly increases ADG and G:F and reduces morbidity and mortality levels in wean-to-finish pigs.