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Rapid fluctuations in ambient temperature before conception reduce fetal viability in replacement gilts
Recently, we determined that rapidly cooling pigs after acute heat stress (HS) resulted in a pathological condition, and because rapid temperature fluctuations are associated with seasonal infertility in sows it could be hypothesized that these conditions are linked. To determine the effects of rapid temperature fluctuations on reproductive efficiency, 36 replacement gilts (137.8 ± 0.9 kg BW) were estrus synced and then 14.1 ± 0.4 d after estrus was confirmed, gilts were exposed to thermoneutral conditions (TN; n=12; 19.7 ± 0.9°C) for 6 h, or HS (36.3 ± 0.5°C) for 3 h, followed by a 3 h recovery period (R) of rapid cooling (HSRC; n=12; immediate TN exposure and cold water dousing) or gradual cooling (HSGC; n=12; gradual decrease to TN conditions) over two consecutive d. Vaginal (TV) and gastrointestinal tract temperatures (TGI) were obtained every 15 min, and blood was collected on d 1 and 2 during the HS and R periods at 180 and 60 min, respectively. Pigs were bred 8.3 ± 0.8 d after thermal treatments, and then approximately 28.0 ± 0.8 d after insemination reproductive tracts were collected and total fetus number and fetal viability were recorded. Overall, HS increased TV and TGI (P=0.01; 1.07 and 0.88ºC, respectively) in HSRC and HSGC compared to TN pigs, but no differences were detected between HSRC and HSGC pigs. During R on d1 and d2, TV was reduced from 15 to 105 min (P=0.01; 0.33ºC) in HSRC compared to HSGC pigs, but no overall differences in TGI were detected (P<0.05; 39.67ºC). Rapid cooling increased (P<0.05) circulating TNFα compared to HSGC and TN pigs during R-d1 (55.2%), HS-d2 (35.1%), and R-d2 (64.9%); however, no differences were detected between HSGC and TN pigs. Through R-d1, [insulin]:[glucose] was greater in HSRC versus HSGC and TN pigs (P=0.01; 50.0 and 41.2%), and reduced (29.4%) in HSGC compared to TN pigs. On R-d2, [insulin]:[glucose] tended to be greater (P=0.07; 25.0%) in HSRC compared to HSGC pigs. The estrus interval increased (P=0.01; 4.5 d) in HSRC and HSGC treatments compared to TN controls. Viable fetuses tended to be reduced (P=0.08; 10.5%) and moribund fetuses tended to be increased (P=0.09; 159.3%) in HSRC compared to HSGC and TN pigs, but no differences were detected between HSGC and TN pigs. In summary, rapid temperature fluctuations before conception increase circulating cytokines and insulin resistance and this may be linked to reduced fetal viability.
Keywords: pigs, fetal viability, heat stress, temperature fluctuations