Impact of heat stress and metabolic endotoxemia on porcine ovarian function

Heat stress (HS) results from an imbalance of thermal energy, and economic losses due to HS cost the U.S. swine industry approximately S900 million annually. HS negatively influences a variety of parameters affecting reproduction: spontaneous abortion, longer wean-to-estrus interval, delayed puberty, reduced litter size, and total number bom. all of which culminate in seasonal infertility. Additionally. HS compromises intestinal integrity ultimately leading to metabolic endotoxemia (ME) and increased systemic lipopoly-saccharide (LPS), an endotoxin originating from the cell wall of gram-negative bacteria. Toll-like receptor 4 (TLR4) is a membrane bound receptor protein that binds LPS. initiating a signaling cascade that involves phosphorylated nuclear factor kappa B (pNFkB) and pro-inflammatory cytokine release. Acyloxyacyl hydrolase (AOAH) cleaves the lipid A moiety from LPS and is thereby involved in LPS detoxification. We hypothesized that ME contributes to seasonal infertility in swine. The study objectives were to characterize the impact of HS and ME on ovarian function. Twelve post-pubertal gilts (126.0 ±21.6 kg) were synchronized for 14 d by orally administering Matrix® to ensure that gilts were heat-stressed during the follicular phase of the estrous cycle. Immediately after Matrix® withdrawal, gilts were split in two groups (w = 6) and exposed to cyclical HS or thermal neutral (TN) conditions for 5 d and then sacrificed. Gilts were exposed to either constant TN conditions (20.3 ± 0.5°C) or cyclical HS (25.4-31.9°C) To imitate a diurnal heat load pattern. Ovaries were collected at the end of the experimental period and TLR4, PNFkB, and AOAH protein abundance were quantified in whole ovarian lysate. Relative to TN ovaries. HS increased (P < 0.05) TLR4 (16%) and pNFkB (11%) protein abundance. There was no difference in AOAH abimdance (P > 0.05) between TN and HS ovaries. This data suggests that the ovaiy is responsive to ME and that HS can induce a pro-inflammatory environment in the ovaiy. which could contribute to compromised fecundity in heat-stressed swine. This work was supported by the National Pork Board.