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Title: Effects of rapid temperature fluctuations prior to breeding on reproductive efficiency in replacement gilts

item Johnson, Jay
item MARTIN, K - Purdue University
item POHLER, K - University Of Tennessee
item STEWART, K - Purdue University

Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2016
Publication Date: 8/19/2017
Citation: Johnson, J.S., Martin, K.L., Pohler, K.G., Stewart, K.R. 2017. Effects of rapid temperature fluctuations prior to breeding on reproductive efficiency in replacement gilts. Journal of Thermal Biology. 61:29-37. doi: 10.1016/j.jtherbio.2016.08.003.

Interpretive Summary: Climate change threatens the sustainability of animal agriculture and can negatively impact the health and development of livestock at all stages of production. The agriculture sector contributes $200 billion annually to the US economy; however, it is the most vulnerable to climate change and it is estimated that the U.S. swine industry loses more than $300 million per year due to heat stress-related losses in productivity. Of these losses, seasonal infertility due to heat stress is estimated to cost producers $55 per sow each year despite improved cooling systems and management practices. Seasonal infertility has been recognized as a potential economic loss to the swine industry since the late 1970’s and is characterized by prolonged wean-to-mate intervals, reduced conception rates, reductions in farrowing rate and embryonic survival, and a reduction in pigs weaned per litter. Alterations in nutrition, photoperiod, housing, insulin action, and rapid temperature fluctuations have been suggested as potential causes, although there appears to be little consensus regarding the specific mechanism of action. The objective of this study was to determine the effects of rapid reductions in ambient temperature after acute heat stress on future reproductive success in replacement gilts. Eight days prior to breeding, pigs were subjected to either thermoneutral conditions, or two consecutive days of acute heat stress followed by either rapid cooling (immediate exposure to thermoneutral conditions and ice water dousing) or gradual cooling (gradual reduction in room temperature). Our previous research indicated that rapid cooling results in greater immune system activation and this was confirmed in the present study. Due to this immune system activation, sows became insulin resistant and it is likely that this contributed to a reduction in fetal viability when determined 28 days after breeding. In conclusion, reducing sow exposure to rapid changes in ambient temperature can reduce the negative impact of heat stress on reproductive efficiency. Producers aiming to reduce pregnancy losses during summer months should closely monitor their cooling systems to ensure that rapid fluctuations in barn temperature do not occur.

Technical Abstract: Recently, we determined that rapidly cooling pigs after acute heat stress (HS) resulted in a pathological condition, and because rapid temperature fluctuations are often associated with reduced reproductive success in sows it lends itself to the hypothesis that these conditions may be linked. Study objectives were to determine the effects of rapid temperature fluctuations on future reproductive success in pigs. Thirty-six replacement gilts (137.8 ± 0.9 kg BW) were estrus synced and then 14.1 ± 0.4d after estrus was confirmed, gilts were exposed to thermoneutral conditions (TN; n = 12; 19.7 ± 0.9°C) for 6h, or HS (36.3 ± 0.5°C) for 3h, followed by a 3h recovery period of rapid cooling (HSRC; n = 12; immediate TN exposure and cold water dousing) or gradual cooling (HSGC; n = 12; gradual decrease to TN conditions) repeated over 2d. 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 recovery periods at 180 and 60 min, respectively. Pigs were bred 8.3 ± 0.8d after thermal treatments over 2 consecutive d. Approximately 28.0 ± 0.8d 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 recovery, 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 TNFa compared to HSGC and TN pigs during recovery d1 (55.2%), HS-d2 (35.1%), and recovery d2 (64.9%); however, no differences were detected between HSGC and TN pigs. Through recovery 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 recovery d2, [insulin]:[glucose] tended to be greater (P = 0.07; 25.0%) in HSRC compared to HSGC pigs. Days to estrus were increased (P = 0.01) by 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 increase the systemic cytokine response and insulin resistance, and this may contribute to reduced fetal viability and reproductive success in pigs.