Genetics Affect Incidence of Porcine Circovirus Associated Disease

University of Nebraska 2007 Swine Report. Porcine Circovirus Associated Disease (PCVAD) reduces productivity and causes serious economic loss. Genetic variation in resistance to diseases, including PCVAD, is known to exist. In 2002, symptoms of PCVAD in pigs from the University of Nebraska swine population were first observed. Symptoms were limited to five genetic lines that are Landrace/Large White composites: three lines selected for increased litter size and growth rate (Lines 2, 24, and 45), and controls for these selection lines (Lines 16 and 61). PCVAD has not been observed in crossbred pigs from mating the selection lines with other breeds. Generation 24 pigs within these lines were scored for PCVAD based on signs of muscle wasting, rough hair coat, respiratory problems, and growth retardation. Necropsies were performed on a sample of animals expressing symptoms of PCVAD to confirm PCVAD and to determine other infections present in these pigs. Using the foster dam as the maternal genetic effect, direct and maternal heritability estimates were 0.23 + 0.11 and 0.03 + 0.06, respectively, with a common foster litter effect of 0.14 + 0.06. Using the birth dam as the maternal genetic effect, direct and maternal heritability estimates were 0.07 + 0.12 and 0.26 + 0.14, respectively. Incidence of PCVAD was greater in selection lines than control lines (18.5 vs. 5.0%; P = 0.06). Significant differences between PCVAD- and non-PCVAD-pigs were observed for birth weight (0.21 lb, P < 0.10), weaning weight (1.21 lb, P < 0.05), 70-day weight (12.6 lb, P < 0.05), and 180-day weight (48.5 lb, P < 0.01). Inbreeding affected incidence of PCVAD in Line 2 (P < 0.05), but not in other lines. Incidence also varied between areas of the farm in which pigs were raised (P < 0.05). Necropsies confirmed PCVAD in all 21 pigs necropsied, 11 of the 21 pigs also had Mycoplasma hyopneumoniae infection. Differences in line, inbreeding, management practices, and exposure to other pathogens influence expression of PCVAD.