Evaluation of sow thermal preference across three stages of reproduction

Authors: ROBBINS, LINDSEY - Purdue University; GREEN-MILLER, ANGELA - Purdue University; Lay Jr, Donald; SCHINCKEL, ALLAN - Purdue University; Johnson, Jay; GASKILL, BRIANNA - Purdue University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2021
Publication Date: 7/1/2021
Citation: Robbins, L.R., Green-Miller, A.R., Lay Jr, D.C., Schinckel, A.P., Johnson, J.S., Gaskill, B.N. 2021. Evaluation of sow thermal preference across three stages of reproduction. Journal of Animal Science. https://doi.org/10.1093/jas/skab202.
DOI: https://doi.org/10.1093/jas/skab202

Interpretive Summary: Heat stress causes infertility and reproductive inefficiency in sows and has a negative effect on developing offspring that lasts throughout their lifetime. Although heat stress can alter various gestating sow performance measures, current temperature recommendations do not reflect thermal preference differences based on reproductive stage. Additionally, current recommendations are based on data from >35 years ago and likely do not reflect thermal preference ranges in modern high producing commercial sows. Therefore, the study objective was to determine the preferred temperature of sows at three reproductive stages including not-pregnant, mid-gestation, and late-gestation. We hypothesized that temperature preference of sows would be lower with advancing gestation. It was determined that late-gestation sows preferred cooler temperatures when compared to mid-gestation and not-pregnant sows, but no differences were detected between not-pregnant and mid-gestation sows. Furthermore, the temperature preference range of all sows was at the lower end of the current recommended range suggesting that exposure to temperatures at the higher end of current recommendations may be uncomfortable for modern sows. Results from this study suggest that current sow temperature recommendations should be updated to reflect differences by reproductive stage and preferences of modern commercial sows.

Technical Abstract: Heat stress (HS) negatively affects swine well-being, resulting in greater morbidity and mortality, and reduced welfare continues to occur despite advances in management strategies. The first step in developing heat mitigation strategies is to identify the thermal comfort zone (TCZ) of sows. Currently, the Guide for the Care and Use of Agricultural Animals in Research and Teaching (Federation of Animal Science Societies, 2010) states that the recommended temperature range for sows and boars over 100 kg is between 10 to 25°C. Studies in humans and rodents have shown that thermal comfort can be dependent upon reproductive stage and current swine guidelines do not reflect this. Thus, the study objective was to evaluate whether different reproductive stages of sows altered their thermal preference. Twenty multi-parous sows (3.4 ± 48 1.2 parity) in different reproductive stages (open: not pregnant, n=7; mid-gestation: 58.5 ± 5.68 49 d, n=6; and late-gestation: 104.7 ± 2.8 d, n=7) were tested. Thermal preference, where individually tested sows freely choose a temperature, was determined using a thermal gradient of 10.4 to 30.5°C. Sows were given 24 h to acclimate to the thermal apparatus. Before testing began, sows were given daily feed allotment and returned to the apparatus. Video from the 24 h test period was used to record sow behavior (time spent inactive), posture (upright, sternal and lateral lying), and location using instantaneous scan samples every 10 min. Data were analyzed using PROC MIXED in SAS 9.4. A cubic regression model was used to calculate the sow’s most preferred temperature based on the location, or temperature, in which they spent the most time. The preference range was calculated using peak temperature preference ±SE for each sow. Reproductive stage altered where sows spent their time within the thermal gradient (P < 0.01). Late-gestation sows preferred cooler temperatures (14.0°C) than mid-gestation (14.8°C; P < 60 0.01) and open sows (14.8°C; P < 0.01). In summary, sow thermal preferences were within the lower half of the current recommended range (10 to 25°C). This indicates that temperatures at the higher end of the recommended range could be uncomfortable to sows and that the TCZ of sows may be narrower than recommendations indicate.