Effects of different antibiotic feeding programs on morbidity and mortality and growth performance of nursery pigs housed in a wean-to-finish facility

The objective of this study was to evaluate the effects of two antibiotic feeding programs in comparison to nonmedicated controls on the incidence of morbidity and mortality and growth performance of nursery pigs in a commercial setting. The study used 2,250 crossbred pigs in a randomized complete block design (blocking factor = start date). There were two dietary phases with three treatments in each phase: 1) nonmedicated controls vs. 2) 39 mg/kg (35 g/ton) tiamulin + 441 mg/kg (400 g/ton) chlortetracycline fed for 14 d (TIACTC) followed by 39 mg/kg (35 g/ton) tiamulin fed for 21 d (TIA) vs. 3) 28 mg/kg (25 g/ton) carbadox + 441 mg/kg (400 g/ton) oxytetracycline fed for 14 d (CAROTC) followed by 55 mg/kg (50 g/ton) carbadox fed for 21 d (CAR). Necropsy results from mortalities during the study confirmed the presence of pathogens including Pasteurella multocida and Escherichia coli, as well as Mycoplasma hyopneumoniae, Haemophilus parasuis, and Streptococcus suis. The study was carried out for a fixed time of 35 d from 6.7 ± 0.57 to 25.5 ± 2.23 kg BW. Pigs were housed in single-sex pens of 25 in a commercial wean-to-finish facility and there were 30 replicates of each treatment. All pigs were weighed as a group (i.e., pen) on days 0 (start), 14, and 35 (end) of study. Pigs had ad libitum access to feed and water throughout the study period; all feed additions to the feeder were recorded. There was no effect (P > 0.05) of antibiotic feeding program on the incidence of morbidity and mortality at any point during the study. During phase 1, TIACTC- and CAROTC-fed pigs were heavier (P < 0.05) at day 14 and had greater (P < 0.05) ADG (8.3% and 5.6% for TIACTC and CAROTC, respectively) and ADFI (4.3% and 6.5%, respectively) than controls. Pigs fed TIACTC in the first 14 d had greater (P < 0.05) G:F than the other treatments, which were similar for this measurement. In phase 2, feeding CAR resulted in greater (P < 0.05) ADG than controls, with pigs fed TIA being intermediate and different (P < 0.05) than the other treatments. Feeding antibiotics, regardless of treatment, resulted in greater (P < 0.05) ADFI than controls, but there were no differences in G:F. For the overall 35-d study period, feeding antibiotics resulted in greater (P < 0.05) ADG than controls (3.8% and 5.8%, respectively), but no difference (P > 0.05) between treatments for overall G:F. The results of this study confirm the advantage of feeding antibiotics on nursery pig growth.