Effects of in utero heat stress and genomic selection for heat tolerance on semen quality and sperm physiology in boars

Authors: MCANALLY, BROOKE - University Of Nebraska; ROSS, CAITLIN - University Of Nebraska; AHERN, DANIEL - University Of Nebraska; BYRD, MARYKATE - Purdue University; MUSA, JACOB - Purdue University; ELSE-KELLER, ALEXANDRA - Iowa State University; KERNS, KARL - Iowa State University; Lents, Clay; BRITO, LUIZ - Purdue University; JOHNSON, JAY - University Of Missouri; DESAULNIERS, AMY - University Of Nebraska

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/25/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Reduced semen quality in boars is a reproductive consequence associated with in utero heat stress (IUHS). Specifically, IUHS boars exhibit a 23% decrease in total sperm production, a 74% increase in tail abnormalities, and multiple alterations in sperm kinematics. However, no prior studies have investigated the effects of IUHS on sperm physiology, including acrosomal integrity, zinc signature (biomarker of capacitation), and oxidative stress. Further, genomic selection for greater heat tolerance may offer a practical solution to safeguard against the negative reproductive consequences of IUHS. The primary objective of this study was to evaluate semen quality and sperm health in boars gestated under IUHS or in utero thermoneutral (IUTN) conditions whose parents were genomically selected for greater heat tolerance (TOL) or sensitivity (SEN). Pregnant crossbred dams were subjected to cyclic heat stress (26–36°F) or thermoneutral (17–20°F) conditions between gestational days 6–70. Male offspring were categorized as IUHS+SEN (n = 8), IUHS+TOL (n = 8), IUTN+SEN (n = 9), or IUTN+TOL (n = 6). Semen was collected weekly from each boar for 10 weeks. Ejaculates were analyzed using computer-assisted sperm analysis (CASA). One ejaculate per boar was analyzed via image-based flow cytometry (IBFC) to assess viability, acrosomal integrity, zinc signature, and oxidative stress both pre- and post-capacitation; change in each variable (e.g., percent intact acrosome) was also calculated. Data were analyzed using PROC MIXED in SAS, with boar as the experimental unit. For CASA data, treatment was considered the fixed effect in the final model, with semen collector, CASA evaluator, and time between collections included as covariates when necessary. For IBFC data, treatment was considered the fixed effect, with collection week included as a covariate. There was an overall treatment effect for progressive motility (P=0.0134) and slow sperm (P=0.0159). Specifically, within the TOL genotype, IUHS boars had a greater number of slow sperm compared with IUTN boars (P=0.0413); but overall, IUHS+TOL boars tended to have a greater proportion of slow sperm than IUHS+SEN boars (P=0.0608). Moreover, IUHS+SEN boars tended to have an increased number of sperm with normal morphology versus IUHS+TOL boars (P=0.1023). The percentage of sperm with the distal midpiece reflex (DMR; associated with total number born) differed between treatment groups (P=0.0025). IUHS+TOL boars experienced an 8-fold greater percentage of DMR than IUTN+TOL boars (P=0.0108). Further, in IUHS boars, the TOL genotype had a greater number of sperm with DMR than the SEN genotype (P=0.0205). In addition, sperm from IUHS+SEN boars had an altered head shape compared with IUTN+SEN boars (P=0.0358). For IUHS boars, TOL boars tended to have a reduced head elongation score compared to SEN boars (P=0.0592). Post-capacitation, IUHS+TOL animals had a lower proportion of sperm that underwent the acrosome reaction compared with IUTN+TOL boars (P=0.0256). Based on these data, IUHS compromises aspects of sperm structure, motility and function in mature boars, with several effects dependent on genotype. The USDA is an equal opportunity employer.