Evaluation of antibiotic usage during late gestation on pelvic organ prolapse incidence in sows

Throughout the last decade, rising sow mortality rates have afflicted U.S. pork producers, as mortality rates have increased from an average of 9.0% in 2014 to 12.5% in 2024. Part of this increase is due to increased incidence of pelvic organ prolapse (POP), which accounted for 22.6% of sow mortality in 2023. Despite widespread acknowledgement of this issue, mitigation strategies are lacking. Antibiotics represent a potential strategy to reduce POP incidence, as a 2019 survey reported POP incidence was lower when feed contained antibiotics compared to periods without antibiotics. Therefore, this study examined the effect of bacitracin methylene disalicylate (BMD) supplementation on POP incidence in late-gestation sows across two commercial farms. Administration of BMD differed between farms, with farm A administering BMD through the water and farm B administering BMD through the feed. A total of 1,014 sows were on trial at farm A, with 522 in the control group and 492 in the BMD group. A total of 1,275 sows were on trial at farm B, with 709 in the control group and 566 in the BMD group. Sows were administered BMD for approximately two weeks prior to farrowing and perineal score (PS) evaluations were conducted to determine presumed POP risk. In brief, a PS of 1 (PS1) presumes low risk of POP while a PS of 3 (PS3) presumes high risk of POP determined by protrusion and swelling of the perineal region. Analysis of PS between treatments revealed that BMD administration did not affect PS at either farm (P ≥ 0.13). At farm A, 60.0% of control sows and 60.6% of BMD treated sows were scored PS1 while 2.9% of control sows and 5.4% of BMD treated sows were scored PS3. At farm B, 78.3% of control and 76.7% of BMD sows were scored PS1 while 2.8% of control and 3.1% of BMD sows were scored PS3. Further, BMD did not affect POP incidence at either farm (P ≥ 0.71), with 2.7% of control sows and 2.8% of BMD sows experiencing POP at farm A, and 2.8% of control sows and 3.2% of BMD sows experiencing POP at farm B. When evaluating litter characteristics, BMD treated sows had a lower number of stillborn piglets compared to control (P ≤ 0.05), although this observation is largely due to PS3 scored sows treated with BMD having lower stillborns compared to PS3 control sows. Although BMD administration did not reduce POP incidence in the current study, further investigation into the effect of BMD on incidence of stillborn piglets is warranted.