Mitigation of summertime boar infertility by evaporative and conductive cooling

Abstract

Boars subjected to summertime temperatures results in reductions in sperm quality. This reduction in quality is associated with decreases in both litter size and conception rate. With this study we aim to quantify the benefits of using additive cooling strategies on both testicular temperature and sperm quality. Thermal conditions were measured with temperature and humidity sensors (Onset[copyright] Hobologgers) in eleven commercial boar studs in five states. Large White x Landrace F1 boars (n=12; Choice Genetics[copyright]) were exposed to representative summertime conditions (heat stress, HS; 21.4 to 26.1[degree]C) and heat wave conditions (HW; 24.3 to 31.3[degree]C) utilizing the Brody Environmental Chambers at the University of Missouri. Neck and testicular drippers (3.8 liters per hour) with and without forced air (2.8 cubic meters per minute) were applied directly to each boar in a Latin square design with three day periods. Nooyen[copyright] Cool Sow Floor was tested with each boar under HS and HW using a switchback design with a seven day period. Shoulder, ear, scrotal, and rectal temperatures as well as respiration rate at 0700 and 1500 hours were recorded. Boars were implanted surgically with two temperature sensing telemetry devices (Anipill[trademark] Temperature Implant, Data Sciences International; St. Paul, MN): one implanted between the peritoneum and the body wall (core temperature); the other sutured between the testicular tunics (testicular temperature). The initial selection for the most effective strategy was the treatment able to maintain the core-testicle temperature at the proper 2 - 4[degree]C differential. However, due to poor quantity of data collected in the preliminary trials, the selection was based on the most advantageous combination of thermal response variables. The most advantageous combination of response variables was observed in the evaporative strategy utilizing drippers and fans directed onto the neck and scrotum of the boar. Subsequently, six boars were provided the most effective strategy and six received no mitigation with all boars held under HS conditions. The implanted device data showed that mitigated boars had significantly lower testicular temperatures than unmitigated counterparts (33.1+0.4[degree]C vs. 33.9+0.4[degree]C, P <0.001). However, core temperature did not vary significantly between boars. Shoulder surface temperature was lower in mitigated boars compared to unmitigated boars (29.2+0.4, 33.5+0.4, respectively, P<0.0001). Ear and scrotal surface followed the same trend with mitigated boars (28.2+0.8, 28.8+0.3, respectively) exhibiting lower temperatures compared to their unmitigated counterparts (31.2+0.8, 31.7+0.3, respectively) with statistical differences observed for both measures (P,<0.03 and <0.0001, respectively). Respiration rate was not different between mitigated and unmitigated boars (P=0.125). After 56 days boars were slaughtered and sperm collected from the epididymides of each boar. One hundred spermatozoa were classified according to physical morphology for both epididymal samples from each boar. Unmitigated boars exhibited higher proportions of tail (59.4+3.5) and head (15.3+1.5) related defects compared with mitigated boars (37.7+3.5, 8.0+1.5, respectively and P=0.0003 and 0.003, respectively). Mitigated boars had significantly higher proportions of morphologically normal sperm than unmitigated boars (40.5+3.2, 13.3+3.2, respectively P<0.0001). Further sperm analysis was conducted using an image-based flow cytometer measuring DNA fragmentation (TUNEL) ubiquitination (anti-ubiquitin/UBB antibody), surface glycosylation (lectin LCA), and acrosomal abnormalities (lectin PNA). No significant differences were observed between mitigated and unmitigated boars due to large amounts of individual variation within treatment. Even under relatively mild thermal stress representative of commercial boar studs in the US, opportunities to improve sperm quality through cooling exist.