Impacts of Climate Change on Reproduction
Session: Poster Session A
Amy T. Desaulniers, PhD
Associate Professor
University of Nebraska-Lincoln
Heat stress is a well-established threat to boar reproductive performance. However, the long-term reproductive consequences of in utero heat stress (IUHS) are only beginning to be understood. For example, IUHS negatively affects boar semen quality, but the underlying mechanisms are undefined. Recent data from our group suggests that IUHS alters neonatal testis composition and pre-pubertal circulating cytokine profiles, which may contribute to IUHS-induced subfertility. Genomic selection for improved heat tolerance may be a novel approach to circumvent IUHS-induced fertility consequences. The main objective was to evaluate pubertal development of boars gestated in IUHS or in utero thermoneutral (IUTN) conditions from parents genomically selected for heat tolerance (TOL) or sensitivity (SEN). White crossbred TOL or SEN dams experienced either cyclic heat stress (26-36°F) or thermoneutral (17-20°F) conditions from gestational d 6-70, resulting in four progeny treatment groups: IUHS+SEN, IUHS+TOL, IUTN+SEN, and IUTN+TOL. Body weights were recorded on boars (n = 9-10/treatment) at d 0, 30, 60, 100, 150, 190, and 225 of age. Testis length and width were also recorded to calculate predicted testis volume. Pubertal attainment was defined as the first detection of at least one spermatozoon in urine, based on weekly samples collected starting at d 120 of age. Beginning at d 180, boars were exposed weekly to a dummy sow for semen collection training over 9 weeks. Boars also received a libido score using a 5-point scale (1 = no interest, 2 = some interest, 3 = mounting with no erection or erection with no mounting, 4 = mounting with erection, and 5 = mounting and semen collection). Data were analyzed via the MIXED procedure of SAS with a model that included boar as the experimental unit and treatment as the fixed effect. Time and the treatment x time interaction were included when appropriate. Body weight was included as a covariate for predicted testis volume. Binary data were analyzed via PROC GLIMMIX with a logit link function. Body weight and predicted testis volume increased over time (P < 0.0001). A treatment by time interaction was detected (P=0.0082) for body weight, but weights did not differ at any individual time point based on genotype or thermal exposure (P >0.10). An overall treatment effect was detected for predicted testis volume (P < 0.05), suggesting an effect on Sertoli cells that govern testis size and sperm production capacity. Specifically, IUHS+TOL boars exhibited a greater predicted testis volume compared with IUHS+SEN (271.07±8.85 versus 260.23±8.82, respectively; P<0.01) and IUTN+SEN (271.07±8.85 versus 262.56±8.85, respectively; P=0.04) boars. A tendency for predicted testis volume to differ was also observed between IUHS+TOL and IUTN+TOL (271.07±8.85 versus 263.92±8.82; P=0.07) boars. Neither age at puberty (P >0.10) nor age at first collection (P >0.10) differed. Libido score increased over time (P < 0.0001), and a tendency for a treatment x time interaction was detected (P=0.0813). For example, IUTN+SEN boars either tended to have a greater libido score (week 3; P=0.0934) or had significantly greater libido scores (weeks 4 and 5; P < 0.02) compared with IUHS+SEN boars, indicating that IUHS affects the development or display of sexual behavior during early puberty. The overall percentage of boars successfully trained did not differ (P=0.3824). In conclusion, these results suggest that IUHS affects testicular growth during pubertal development; however, genomic selection for heat tolerance may counteract these effects, supporting normal testicular development to optimize boar fertility.