Birth weight, intrauterine growth retardation and fetal susceptibility to porcine reproductive and respiratory syndrome virus

Authors: LADINIG, ANDREA - University Of Saskatchewan; FOXCROFT, GEORGE - University Of Saskatchewan; ASHLEY, CAROLYN - University Of Saskatchewan; Lunney, Joan; PLASTOW, GRAHAM - University Of Alberta; HARDING, JOHN - University Of Saskatchewan

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2014
Publication Date: 9/22/2014
Publication URL: https://handle.nal.usda.gov/10113/61339
Citation: Ladinig, A., Foxcroft, G., Ashley, C., Lunney, J.K., Plastow, G., Harding, J.C. 2014. Birth weight, intrauterine growth retardation and fetal susceptibility to porcine reproductive and respiratory syndrome virus. PLoS One. 9:10.

Interpretive Summary: Porcine Reproductive and Respiratory Syndrome (PRRS) causes major losses to the pig industry, $642,000/year in the US alone. For breeding herds losses are due to abortions, early farrowings, fetal death, as well as the birth of weak, congenitally infected piglets resulting in elevated pre-weaning mortality. For this study the severity of PRRS was compared in pregnant gilts originating from high and low birth weight litters. Previous work had shown that low birth weight gilts have low birth weight fetuses and we wanted to know whether they might be more susceptible to PRRS virus infection. One-hundred and eleven pregnant gilts were experimentally infected with PRRS virus in their third trimester and were necropsied along with their fetuses 21 days later. When reproductive traits were analyzed; ovulation rates and litter size did not differ between the high and low birth weight groups. As expected, fetuses from low birth weight gilts were shorter, lighter and demonstrated evidence of asymmetric growth with large brain:organ weight ratios (i.e. brain sparing growth). When anti-PRRS responses were compared between high and low birth weight gilts, most parameters (viral load in serum and tissues, gilt serum cytokine levels, and litter outcome, including the percent dead fetuses per litter) did not differ by birth weight group. The only difference was that an important blood cell subset, gamma/delta T cells, was significantly decreased over time in high compared to low birth weight gilts. Overall, this study provided no substantive evidence that the severity of PRRS is affected by sow birth weight. Taken together, this study clearly affirmed that birth weight is a transgenerational trait in pigs, and provided evidence that larger fetuses are more susceptible to transplacental PRRSv infection.

Technical Abstract: The severity of porcine reproductive and respiratory syndrome was compared in pregnant gilts originating from high and low birth weight litters. One-hundred and eleven pregnant gilts experimentally infected with porcine reproductive and respiratory syndrome virus on gestation day 85 (±1) were necropsied along with their fetuses 21 days later. Ovulation rates and litter size did not differ between groups, but fetuses from low birth weight gilts were shorter, lighter and demonstrated evidence of asymmetric growth with large brain:organ weight ratios (i.e. brain sparing). The number of intrauterine growth retarded fetuses, defined by brain:organ weight ratios greater than 1 standard deviation from the mean, was significantly greater in low, compared to high, birth weight gilts. Although gamma/delta T cells significantly decreased over time in high compared to low birth weight gilts, viral load in serum and tissues, gilt serum cytokine levels, and litter outcome, including the percent dead fetuses per litter, did not differ by birth weight group. Thus, this study provided no substantive evidence that the severity of porcine reproductive and respiratory syndrome is affected by dam birth weight. However, intrauterine growth retarded fetuses had lower viral loads in both fetal thymus and in endometrium adjacent to the umbilical stump. Crown rump length did not significantly differ between fetuses that survived and those that died at least one week prior to termination. Taken together, this study clearly demonstrates that birth weight is a transgenerational trait in pigs, and provides evidence that larger fetuses are more susceptible to transplacental PRRSv infection.