Abstract
The trial objective was to compare the performance and animal health parameters of pigs raised according to one of 3 antibiotic (AB) protocols: standard AB medication consisting of mass treatment on days 4 and 21 and judicious AB therapy given therapeutically thereafter as group medication in water and feed or by individual injection (group T1, N = 702); modified AB medication identical to group T1 but with mass treatment only on day 4 and without subsequent therapeutic feed medication (group T2, N = 675); or an antibiotic-free (ABF) regimen (group T3, N = 702). All pigs were vaccinated with a modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine 3 days after weaning. Using a seeder pig model to mimic endemic field infection dynamics, pigs were contact-challenged with virulent PRRSV lineage 1 strain 174 four weeks after vaccination. At finishing, average daily gain (ADG) and mean feed conversion ratio (FCR) were significantly better (p ≤ 0.05) for the T1 and T2 groups compared to the T3 group. There were no significant differences in post-weaning ADG and FCR between the T1 and T2 groups. Mortality and removals significantly favored (p ≤0.05) the T1 and T2 groups (20.94% and 24.89%, respectively) versus the T3 group (57.98%). Net revenue per pig was $105.43, $98.79, and $33.81 for the T1, T2 and T3 groups, respectively. Under the conditions of this study, these results indicate that in a PRRSV-endemic setting involving bacterial co-infections, an ABF production strategy may leave pigs at considerable risk of exposure to severe clinical disease and that judicious use of antibiotics can significantly improve animal health.
Highlights
There is growing advocacy for antibiotic-free (ABF) livestock production to minimize the emergence of antibiotic-resistant food-borne pathogens and subsequent human exposure to these treatment-refractory organisms [1,2,3,4] This trend has been driven by the escalating presence of antibiotic resistance, including multi-drug resistance, among a variety of important bacterial pathogens that infect both animals and humans [5,6]
In the U.S, the regulatory community and the pork industry have been responsive to proposals for reducing AB use in livestock by no longer allowing ABs to be used for growth promotion in animal feed and by requiring a Veterinary Feed Directive (VFD) authorizing the use of all medically important ABs [16,17]
Open reading frame 5 sequencing confirmed that the positive samples were closely related (99.5–100% homology) to the porcine reproductive and respiratory syndrome virus (PRRSV) 174 used in the inoculum
Summary
There is growing advocacy for antibiotic-free (ABF) livestock production to minimize the emergence of antibiotic-resistant food-borne pathogens and subsequent human exposure to these treatment-refractory organisms [1,2,3,4] This trend has been driven by the escalating presence of antibiotic resistance, including multi-drug resistance, among a variety of important bacterial pathogens that infect both animals and humans [5,6]. Sweden banned the feeding of sub-therapeutic AB feed additives to livestock in 1985 and other European Union countries followed suit by 2006, despite allowing the use of therapeutic ABs on a short-term prescription basis, either for individual-animal or population medication [6,13]. Because the majority of ABs in the U.S and other non-EU countries are used in food animals [5], sub-therapeutic AB feed additives used to promote growth in poultry and livestock have understandably become an inviting target for reduction or elimination [4,6]. In the U.S, the regulatory community and the pork industry have been responsive to proposals for reducing AB use in livestock by no longer allowing ABs to be used for growth promotion in animal feed and by requiring a Veterinary Feed Directive (VFD) authorizing the use of all medically important ABs [16,17]. Beginning on January 1, 2017, U.S swine producers were required to obtain a VFD from a licensed veterinarian in order to use medically important ABs in feed, and to obtain a veterinary prescription when using medically important ABs in water [17]
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