Path from breed-to-finish to off-site nursery to finisher locations
By C. Grace Elijah, Cassandra K. Jones, Jason C. Woodworth, Rachel Palinksi, Chad Paulk, Tom Petznick and Jordan T. Gebhardt
Atypical porcine pestivirus (APPV) is associated with congenital tremors (CT) and splay leg (SL) in piglets of infected dams. The major cost of this virus is increased pre-weaning mortality due to CT or SL interfering with the piglet's ability to nurse and move around the farrowing stall.
A commercial farrow-to-finish farm had increased CT and SL in the farrowing rooms early 2020. Diagnostics on clinically affected pigs' samples identified APPV RNA. No histopathological diagnosis was performed based on consultation with a veterinary anatomic pathologist with experience diagnosing APPV given the PCR positive results and clinical picture.
The farm had no previous clinical cases of CT or SL prior to this investigation. The two hypothesized routes were introduction of replacement gilts or incoming semen doses. Therefore, the objectives of this investigation were to determine the prevalence of clinical APPV cases at the farrow-to-finish farm, understand the route of introduction of APPV into the farrrow-to-finish farm and understand the prevalence of APPV viremia within a population of offspring from a gilt multiplication farm through an off-site nursery and finisher barn.
Farrowing records from the farm were analyzed for the presence of CT or SL of single and multiparous females with affected litters. Blood samples were collected at two different times from the group of intended for replacement gilts for the farrow-to-finish and also the maternal barrows at the isolation nursery barn.
Serum and oral fluids were collected from the same pigs at an off-site finisher barn to assess APPV persistence.
APPV E2 sequences were obtained from a serum sample from a gilt housed at the isolation nursery intended as a replacement gilt for the farrow-to-finish farm, a semen dose utilized at the farrow-to-finish farm, and serum of a clinically affected piglet in the farrowing room on the farrow-to-finish farm.
Overall the APPV prevalence of affected litters within batch farrowing groups ranged from 0 to 31% over the course of this investigation. At the offsite nursery location, pooled serum samples (5 pigs) APPV was detected in 37.5% of pigs on arrival and 77.5% at the conclusion of the nursery period (Figure 1).
When evaluating APPV prevalence in individual pigs within pens, it ranged from 20 to 40%. A subset of outgoing pigs were tested for APPV at the finishing facility.
At the start of the turn, this subset APPV prevalence was 26% while at the end of the turn, a 0% APPV prevalence was found in serum of the same animals.
Oral fluids were collected from pens of all pigs present in the finisher barn. The APPV prevalence was 100% at the pen level in oral fluids sampled at the start and the end of the finisher turn (cycle threshold values ranging from 20.4- 28.7). Sequencing results indicated that the virus circulating in clinically affected piglets were the most similar to an incoming semen dose (98.9% similar).
In summary, introduction of APPV into a naïve herd is associated with an increase in clinical CT and SL. Furthermore, APPV RNA was detectable in serum and oral fluids of asymptomatic animals previously exposed to APPV.
This research presents a rationale for quarantines of all incoming animals on a farm. Additionally, we showed semen screening for APPV is crucial to limit the potential for APPV introduction.
Finally we showed oral fluids may be a viable technique for screening incoming animals for APPV.
Elijah, Palinkski, and Gebhardt are in the Department of Diagnostic Medicine/Pathobiology; Jones and Woodworth, the Department of Animal Sciences and Industry; and Paulk, the Department of Grain Science and Industry, all with Kansas State University. Petznick is with Arkcare.
