Genetic parameters for automatically-measured vaginal temperature, respiration efficiency, and other thermotolerance indicators measured on lactating sows under heat stress conditions

Authors: FREITAS, PEDRO - Purdue University; Johnson, Jay; WEN, HUI - Purdue University; MASKAL, JACOB - 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: Genetics Selection Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2023
Publication Date: 9/20/2023
Citation: Freitas, P.H., Johnson, J.S., Wen, H., Maskal, J., Tiezzi, F., Maltecca, C., Huang, Y., DeDecker, A.E., Schinckel, A.P., Brito, L.F. 2023. Genetic parameters for automatically-measured vaginal temperature, respiration efficiency, and other thermotolerance indicators measured on lactating sows under heat stress conditions. Genetics Selection Evolution. https://doi.org/10.1186/s12711-023-00842-x.
DOI: https://doi.org/10.1186/s12711-023-00842-x

Interpretive Summary: Heat stress is a limiting factor to efficient pig production that negatively impacts economic returns for producers and swine welfare. Genetic selection may be a viable method to improve swine heat stress resilience and increase producer profitability in a changing climate. Therefore, the study objective was to evaluate heritability for automatically-measured vaginal temperature as well as other thermoregulatory and anatomical characteristics in heat stressed lactating sows. It was determined that the heritability estimates for vaginal temperature were moderately heritable, while other thermoregulatory traits such as skin temperature and respiration rate had low heritability. Results from this study indicate that the use of automatically-measured vaginal temperature can be used to advance genetic progress for heat stress resilience in pigs.

Technical Abstract: Background Advances in genetic and genomic selection, nutrition, and management have increased pig performance and resulted in greater metabolic heat production and heat stress (HS) sensitivity due to increased heat gain. Efforts have been made in the identification of novel phenotypes in non-commercial settings and based on small sample sizes. Genetic selection based on direct indicators of HS could capture additional mechanisms involved in HS response and enable more accurate selection for more heat tolerant individuals. Therefore, the main objectives of this study were to estimate genetic parameters for various HS indicators in a commercial population of Landrace x Large White lactating sows measured under HS conditions. The main indicators evaluated were: skin surface temperatures (SST), automatically-recorded vaginal temperature (TV), respiration rate (RR), panting score (PS), body condition score (BCS), hair density (HD), body size (BS), ear size, and respiration efficiency (Reff). Results Traits based on TV presented moderate heritability estimates ranging from 0.15 ± 0.02 to 0.29 ± 0.05. Low heritability estimates were found for SST traits (from 0.04 ± 0.01 to 0.06 ± 0.01), RR (0.06 ± 0.01), PS (0.05 ± 0.01), and Reff (0.03 ± 0.01). Moderate to high heritability values were estimated for BCS (0.29 ± 0.04 for caliper measurements; and 0.25 ± 0.04 for visual assessments), HD (0.25 ± 0.05), BS (0.33 ± 0.05), ear area (EA; 0.40 ± 0.09), and ear length (EL; 0.32 ± 0.07). High genetic correlations were estimated among SST traits (> 0.78) and among TV traits (> 0.75). Similarly, high genetic correlations were also observed between RR and PS (0.87 ± 0.02), BCS measures (0.92 ± 0.04), and ear measures (0.95 ± 0.03). These results indicate that overlapping sets of genes influence these traits. Low to moderate positive genetic correlations were observed between SST and TV (from 0.25 ± 0.04 to 0.76 ± 0.07). Low genetic correlations were observed between TV and BCS (from -0.01 ± 0.08 to 0.06 ± 0.07). Respiration efficiency was positively and moderately correlated with RR (0.36 ± 0.04), PS (0.56 ± 0.03), and BCS (0.56 ± 0.05 for caliper measurements, and 0.50 ± 0.05 for the visual assessments). All other trait combinations were lowly genetically correlated. Conclusions A comprehensive landscape of the heritability and genetic correlation for various thermotolerance indicators in lactating sows was provided. All traits evaluated are under genetic control and heritable, with different magnitudes, indicating that genetic progress is possible for all of them. The results for the genetic correlations evidenced the complex relationship between these traits and confirms the importance of a thermotolerance selection sub-index to improve heat tolerance in pigs.