Increased litter survival rates, reduced clinical illness and better lactogenic immunity against TGEV in gilts that were primed as neonates with porcine respiratory coronavirus (PRCV)

Abstract

Establishing immunological memory in female piglets at a young age with PRCV was effective in inducing a secondary immune response to a limiting dose of virulent TGEV given orally 13-18 days prior to farrowing. Subsequently, because of passive antibody transfer, the offspring of these primed gilts were more efficient in surviving a lethal TGEV challenge. An average survival rate of 89% occurred in 6 litters of piglets from primed gilts that were boosted with 2.8 x 10(6) plaque forming units (PFU) of TGEV whereas 76% of the piglets survived in three litters that suckled primed gilts boosted with 3.0 x 10(5)PFU of TGEV. Non-primed gilts given identical pre-farrowing doses of TGEV had litter survival rates of 63 and 55%, respectively. Moreover, both groups of litters from primed gilts suffered less clinical illness (as measured by the extent of weight loss post-challenge) than control litters. Priming of the piglets as neonates and boosting the pregnant gilts produced an anamnestic systemic immune response and correspondingly higher milk titers in the primed gilts compared to control animals. Thus, priming piglets with PRCV was beneficial in providing resistance to TGEV and could be incorporated into a vaccine strategy that yields better protection against TGEV.

Fig. 1

Serum and milk virus neutralization titers. (A) Geometric mean serum neutralizing antibody titers and standard deviations are shown (high dose, primed gilts=2299±1093; high dose, control gilts=206±173; low dose, primed gilts=916±786; low dose, control gilts 83±10). (B) Geometric mean virus neutralizing antibody titers and standard deviations in milk at day 2 post-farrowing were: high dose, primed gilts=2004±617; high dose, control gilts=374±221; low dose, primed gilts=1176±645 and low dose, control gilts=146±93.

Fig. 2

Pre-challenge neutralization titers. Geometric mean serum neutralization titers for the litters of PRCV-primed and control gilts.

Fig. 3

Post-challenge average daily weights for each group of piglets. Geometric mean weights of piglets from PRCV-primed gilts given the high booster dose (•) or the low booster dose (■) of TGEV compared with the geometric mean weights of piglets of control gilts given the high pre-farrowing dose of TGEV (○) or the low pre-farrowing dose of TGEV (□).