Thermoregulatory and physiological responses of nonpregnant, mid-gestation, and late-gestation sows exposed to incrementally increasing dry bulb temperature

Authors: MCCONN, BETTY - Orise Fellow; GASKILL, BRIANNA - Purdue University; SCHINCKEL, ALLAN - Purdue University; GREEN-MILLER, ANGELA - University Of Illinois; Lay Jr, Donald; Johnson, Jay

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2021
Publication Date: 6/4/2021
Citation: Mcconn, B.R., Gaskill, B.N., Schinckel, A.P., Green-Miller, A.R., Lay Jr, D.C., Johnson, J.S. 2021. Thermoregulatory and physiological responses of nonpregnant, mid-gestation, and late-gestation sows exposed to incrementally increasing dry bulb temperature. Journal of Animal Science. 99(7). https://doi.org/10.1093/jas/skab181.
DOI: https://doi.org/10.1093/jas/skab181

Interpretive Summary: Reproductive stage (i.e., not pregnant, mid-gestation, and late-gestation) can influence heat stress susceptibility in sows due to fetal growth and the effects on heat gain by the sow. However, while it is known that pregnancy can influence the heat stress response in sows, there is a lack of current pertinent literature on how reproductive stage influences a sow’s thermoregulatory and physiological response to increasing environmental heat load, particularly in sows with current genetics. Therefore, the study objective was to determine the thermoregulatory and physiological responses of sows with current genetics exposed to increasing environmental heat load at three reproductive stages: open (not-pregnant), mid-gestation, and late-gestation. Our hypothesis was that late-gestation sows would have a more sensitive thermoregulatory and physiological response to increasing environmental heat load relative to mid-gestation and open sows, and that mid-gestation sows would have a more sensitive thermoregulatory and physiological response to increasing environmental heat load relative to open sows. It was determined that late-gestation sows were more sensitive to increasing ambient temperature when compared to mid-gestation and not pregnant sows, but that no differences in heat stress sensitivity was observed between mid-gestation and not pregnant sows. Results from this study provide valuable information regarding thermoregulatory thresholds of sows at differing reproductive stages, which can be used to better manage pigs during times of heat stress.

Technical Abstract: Gestating sows may be more susceptible to increasing ambient temperatures due to greater metabolic heat production and increased body mass, especially as gestation advances. However, there are little available data on the thermoregulatory and physiological responses of gestating sows with modern genetics exposed to gradually increasing ambient temperatures at different reproductive stages. The study objective was to determine the thermoregulatory and physiological responses of open (not pregnant, n = 12; parity 3.27 ± 0.86), mid-gestation (59.7 ± 9.6 days pregnant, n = 12; parity 3.25 ± 0.83), and late-gestation (99.0 ± 4.8 days pregnant, n = 12; parity 3.33 ± 0.75) sows exposed to increasing ambient temperature (TA). Prior to the experiment (5.0 ± 0.7 d), jugular catheters were placed in all sows. During the experiment, the TA was increased gradually from 19.84 ± 2.15°C to 35.54 ± 0.43°C over 400 min and relative humidity was maintained at 40.49 ± 18.57%. Respiration rate (RR), heart rate (HR), skin temperature, and vaginal temperature were measured, and blood samples were obtained via the jugular catheter every 20 min. Data were analyzed using PROX MIXED in SAS 9.4. Respiration rate began to increase at a lower TA (P < 0.01) in late-gestation sows when compared to mid-gestation and open sows, but no differences were detected between mid-gestation and open sows. Overall, late-gestation sows had greater RR (P < 0.01; 23 ± 2 breaths per min (bpm)) compared with mid-gestation (16 ± 2 bpm) and open (15 ± 2 bpm) sows. In addition, late-gestation sows had overall increased HR (P < 0.01; 84 ± 5 bpm) compared with mid-gestation (76 ± 5 bpm) and open (69 ± 5 bpm) sows. Overall, late-gestation sows had reduced bicarbonate and total carbon dioxide levels (P = 0.02; 23.89 ± 1.97 mmol/L and 25.41 ± 2.07 mmol/L, respectively) compared to mid-gestation (27.03 ± 1.97 mmol/L and 28.58 ± 2.07 mmol/L, respectively) and open (26.08 ± 1.97 mmol/L and 27.58 ± 2.07 mmol/L, respectively) sows. Moreover, late-gestation sows had overall greater nitric oxide levels (P < 0.01; 248.82 ± 34.54 µM) when compared with mid-gestation (110.47 ± 34.54 µM) and open (41.55 ± 34.54 µM) sows. In summary, late-gestation sows appear to be more sensitive to increasing TA as indicated by increased RR when compared to mid-gestation or open sows. Results from this study provide valuable information regarding thermoregulatory thresholds of sows at differing reproductive stages.