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

Authors: Johnson, Jay; WEN, HUI - Purdue University; FREITAS, PEDRO H. - Purdue University; MASKAL, JACOB - Purdue University; HARTMAN, SHARLENE - Purdue University; BYRD, MARY - Purdue University; GRAHAM, JASON - Purdue University; CEJA, GUADALUPE - Purdue University; TIEZZI, FRANCESCO - University Of Florence; MALTECCA, CHRISTIAN - North Carolina State University; HUANG, YIJIAN - Smithfield Foods, Inc; DEDECKER, ASHLEY - Smithfield Foods, Inc; SCHINCKEL, ALLAN - Purdue University; BRITO, LUIZ - Purdue University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2023
Publication Date: 4/27/2023
Citation: Johnson, J.S., Wen, H., Freitas, P.F., Maskal, J.M., Hartman, S.O., Byrd, M.K., Graham, J.R., Ceja, G., Tiezzi, F., Maltecca, C., Huang, Y., Dedecker, A., Schinckel, A.P., Brito, L.F. 2023. 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. Journal of Animal Science. 101. https://doi.org/10.1093/jas/skad129.
DOI: https://doi.org/10.1093/jas/skad129

Interpretive Summary: Climate change and the associated increase in global temperatures has 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 as well as novel traits that can be easily collected on farm and provide accurate and precise predictions of heat stress tolerance regardless of housing conditions is a necessary step. Results from the present study demonstrated that housing conditions had a limited influence on heat stress tolerance phenotypes, several anatomical and thermoregulatory measures were correlated, and that heat stress thresholds were impacted by housing conditions. Results from this study may be applied to large-scale phenotyping initiatives for the development or refinement of genomic selection indexes for heat stress resilience in pigs.

Technical Abstract: An accurate and precise understanding of temperatures that cause heat stress (HS) and phenotypes that indicate HS tolerance is necessary to improve swine HS resilience. Therefore, the study objectives were 1) to identify phenotypes that are indicative of HS tolerance, and 2) to determine moderate and severe HS thresholds 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 d 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, panting score, and ear, shoulder, rump, and tail skin temperature. Vaginal temperatures (TV) were recorded in 10 min intervals using data recorders. Anatomical characteristics were recorded and included 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 a mixed model analyses performed using BLUPF90+ software, 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 (P < 0.05). Finally, for sows housed in naturally and mechanically ventilated facilities, moderate HS thresholds were 27.36 and 26.69°C, respectively, and severe HS thresholds were 26.69 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.