Effects of induced acute phase response in ewes on early embryo survival

Abstract

Early pregnant ewes, 5/6 day post coitus (dpc) were used as a model to study early embryonic loss via gram-positive bacterial infections, such as mastitis. Ewes 5/6 dpc were injected with a gram-positive bacteria cell wall component, peptidoglycanpolysaccharide (PG-PS), to induce an innate immune system acute phase response (APR). The induction of the APR and its reactant molecules, such as cytokines and acute phase proteins (APP), were initiated to study their effects on embryonic loss. Twenty Suffolk ewes were synchronized for estrus and bred by fertile rams. At 4 dpc ewes were anesthetized and catheters were surgically placed in the right rear leg in the caudal vena cava via saphenous vein, as well as in the jugular. Ewes were randomly assigned to treatment groups on 5 dpc, and received either a 60 µg/kg BW dose of PG-PS (n=10) or a sham injection of 0.9% NaCl (n=10) i.v. in the jugular vein contralateral of the catheter. Plasma was collected from jugular and caudal vena cava via the saphenous vein before challenge, followed by post challenge samples every 15 minutes until 2 hours, every hour until 12 hours, and once at 24, 36, and 48 hours. Assays were conducted for APR reactants tumor necrosis factor-α (TNF-α), serum amyloid A (SAA), and haptoglobin (Hp), as well as the pregnancy maintenance hormone, progesterone (P 4). In addition, behavior changes and body temperature were also documented before PG-PS injection followed by every hour for 12 hours and then again at 24, 36, and 48 post challenge. Concentrations of TNF-α and P 4 were quantified using radioimmunoassay, whereas ELISA was used to measure SAA and HP concentrations. Intoxication of day 5/6 pregnant ewes with 60 µg/kg BW PG-PS induced significant differences in TNF-α concentration between sample sites (p<0.001) and treatment groups (p<0.02). SAA and Hp concentrations increased significantly (p<0.0001) in challenged ewes. Fever, loss of appetite, lethargy, and vaginal discharge were documented in all treated ewes, as well as 100 % embryonic loss by 21 dpc. Data from this experiment demonstrate that injection of PG-PS systemically leads to production of APP and behavioral changes characteristic of an APR.