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. 2023 Jan 3:101:skad129.
doi: 10.1093/jas/skad129.

Evaluating phenotypes associated with heat tolerance and identifying moderate and severe heat stress thresholds in lactating sows housed in mechanically or naturally ventilated barns during the summer under commercial conditions

Jay S Johnson  1 , Hui Wen  2 , Pedro H F Freitas  2 , Jacob M Maskal  2 , Sharlene O Hartman  2 , MaryKate Byrd  2 , Jason R Graham  2 , Guadalupe Ceja  2 , Francesco Tiezzi  3 , Christian Maltecca  4 , Yijian Huang  5 , Ashley DeDecker  5 , Allan P Schinckel  2 , Luiz F Brito  2
Affiliations

Evaluating phenotypes associated with heat tolerance and identifying moderate and severe heat stress thresholds in lactating sows housed in mechanically or naturally ventilated barns during the summer under commercial conditions

Jay S Johnson et al. J Anim Sci. .

Abstract

An accurate understanding of heat stress (HS) temperatures and phenotypes that indicate HS tolerance is necessary to improve swine HS resilience. Therefore, the study objectives were 1) to identify phenotypes indicative of HS tolerance, and 2) to determine moderate and severe HS threshold temperatures in lactating sows. Multiparous (4.10 ± 1.48) lactating sows and their litters (11.10 ± 2.33 piglets/litter) were housed in naturally ventilated (n = 1,015) or mechanically ventilated (n = 630) barns at a commercial sow farm in Maple Hill, NC, USA between June 9 and July 24, 2021. In-barn dry bulb temperatures (TDB) and relative humidity were continuously recorded for naturally ventilated (26.38 ± 1.21 °C and 83.38 ± 5.40%, respectively) and mechanically ventilated (26.91 ± 1.80 °C and 77.13 ± 7.06%, respectively) barns using data recorders. Sows were phenotyped between lactation days 11.28 ± 3.08 and 14.25 ± 3.26. Thermoregulatory measures were obtained daily at 0800, 1200, 1600, and 2000 h and included respiration rate, and ear, shoulder, rump, and tail skin temperatures. Vaginal temperatures (TV) were recorded in 10 min intervals using data recorders. Anatomical characteristics were recorded, including ear area and length, visual and caliper-assessed body condition scores, and a visually assessed and subjective hair density score. Data were analyzed using PROC MIXED to evaluate the temporal pattern of thermoregulatory responses, phenotype correlations were based on mixed model analyses, and moderate and severe HS inflection points were established by fitting TV as the dependent variable in a cubic function against TDB. Statistical analyses were conducted separately for sows housed in mechanically or naturally ventilated barns because the sow groups were not housed in each facility type simultaneously. The temporal pattern of thermoregulatory responses was similar for naturally and mechanically ventilated barns and several thermoregulatory and anatomical measures were significantly correlated with one another (P < 0.05), including all anatomical measures as well as skin temperatures, respiration rates, and TV. For sows housed in naturally and mechanically ventilated facilities, moderate HS threshold TDB were 27.36 and 26.69 °C, respectively, and severe HS threshold TDB were 29.45 and 30.60 °C, respectively. In summary, this study provides new information on the variability of HS tolerance phenotypes and environmental conditions that constitute HS in commercially housed lactating sows.

Keywords: climatic resilience; closer-to-biology phenotypes; heat stress; phenomics.

Plain language summary

Climate change and the associated increase in global temperatures have a well-described negative impact on swine production. Therefore, improving swine heat stress resilience is of utmost importance to reduce the deleterious effects of heat stress on swine health, performance, and welfare. Genomic selection for heat stress resilience may be a viable strategy to improve swine productivity in a changing climate. However, identifying environmental conditions that constitute heat stress and deriving novel traits that can be easily collected on farm and provide accurate and precise predictions of heat stress tolerance is a necessary step. The present study demonstrated that housing conditions had a limited influence on heat stress tolerance phenotypes, several anatomical and thermoregulatory measures were correlated, and housing conditions impacted heat stress threshold temperatures. Results from this study may be applied to large-scale phenotyping initiatives to develop or refine genomic selection indexes for heat stress resilience in pigs.

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Conflict of interest statement

No conflict of interest, financial, or otherwise are declared by the author(s). Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. All opinions expressed in this paper are the authors’ and do not necessarily reflect the policies and views of the USDA. The USDA is an equal opportunity lender, provider, and employer.

Figures

Figure 1.
Figure 1.
Minimum, mean, and maximum (A) weather station dry bulb temperature (TDB), (B) weather station relative humidity (RH), and (C) weather station dew point temperature (TDP) by date of the study.
Figure 2.
Figure 2.
Minimum, mean, and maximum (A) mechanically ventilated barn dry bulb temperature (TDB), (B) mechanically ventilated barn relative humidity (RH), (C) mechanically ventilated barn dew point temperature (TDP), (D) naturally ventilated barn TDB, (E) naturally ventilated barn RH, and (F) naturally ventilated barn TDP by day of study during the 4-d period of lactating sow measurements.
Figure 3.
Figure 3.
The daily pattern of (A) mechanically ventilated barn dry bulb temperature (TDB), (B) mechanically ventilated barn relative humidity (RH), (C) mechanically ventilated barn dew point temperature (TDP), (D) naturally ventilated barn TDB, (E) naturally ventilated barn RH, and (F) naturally ventilated barn TDP by hour of the day. Data are presented as arithmetic means ± standard deviation.
Figure 4.
Figure 4.
Vaginal temperature monitor.
Figure 5.
Figure 5.
The (A) ear skin temperature (TES), (B) shoulder skin temperature (TSS), (C) rump skin temperature (TRS), and (D) tail skin temperature (TTS) of lactating sows housed in either mechanically ventilated or naturally ventilated barns by hour of the day. a,b,cLetters indicate differences (P < 0.01) by hour. Data are presented as LSmeans ± SE.
Figure 6.
Figure 6.
The respiration rate (RR) of lactating sows housed in either (A) mechanically ventilated or (B) naturally ventilated barns by hour of the day. a,b,cLetters indicate differences (P < 0.01) by hour. Data are presented as LSmeans ± SE.
Figure 7.
Figure 7.
The vaginal temperature (TV) of lactating sows housed in either (A) mechanically ventilated or (B) naturally ventilated barns by hour of the day. a-tLetters indicate differences (P < 0.01) by hour. Data are presented as LSmeans ± SE.
Figure 8.
Figure 8.
Cubic regression analysis of lactating sow vaginal temperature (TV) as a function of dry bulb temperature (TDB) in (A) mechanically ventilated and (B) naturally ventilated barns. Dashed lines within the figures indicate the inflection points and solid lines within the figures indicate the point at which the TV increased abruptly (+0.20 °C) above baseline TV. The TDB associated with these points are indicated above each line.
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