Impact of a porcine epidemic diarrhea outbreak on swine productivity in Japan: a retrospective cohort study

YAMANE, Itsuro; YAMAZAKI, Hisanori; ISHIZEKI, Sayoko; WATANABE, Yugo; OKUMURA, Hanako; OKUBO, Mitsuharu; KURE, Katsumasa; HAYAKAWA, Yuiko; FURUKAWA, Makoto; OOI, Munetaka; MIZUKAMI, Yoshihiro; ITO, Mitsugu

The study herds were selected from among farrow-to-finish herds that had been entered in the PigINFO system (n=119) between July 2013 and March 2015 (study period). Data associated with the porcine epidemic diarrhea virus (PEDV) infections in each herd were investigated by 15 veterinarians belonging to the Japan Association of Swine Veterinarians (JASV). From 1 April to 30 June 2014 (PED epidemic), any herds with clinical signs of PED and feces that tested positive for PEDV with polymerase chain reaction and/or immunohistochemical staining at local livestock hygiene centers were defined as PED-positive. Herds that showed no clinical signs of PED or were negative for PEDV on the abovementioned laboratory tests were classified as negative. Herds for which there was no information on PED status, with missing data, or in which PED was confirmed before 31 March 2014 were excluded from the study. The final sample sizes in the PED-positive and PED-negative groups were 38 and 61 herds, respectively. For all PED-positive herds, the participating veterinarians recorded the types of barns in which the pigs showed clinical symptoms. In the PED-positive herds, the dates of the initial PED diagnosis and the disappearance of clinical signs from the herd were also recorded by the veterinarians. The PED period for each PED-positive herd was defined as the number of days between the initial PED diagnosis and the disappearance of clinical signs. The PED-positive herds were then further classified into those with a long PED period (≥30 days; L-PED-positive; n=28) and those with a short PED period (<30 days; S-PED-positive; n=10). This cutoff value (30 days) for the PED period was determined by visually inspecting the distribution of PED periods. Thus, the targeted herds were classified into three groups (PEDnegative, L-PED-positive and S-PED-positive), and their productivity, characterized with the production parameters described below, was compared during the study period.