Heat Stress Mitigation Strategies for Boars and Impact of Most Effective on Sperm Parameters

Thermal conditions were measured with temperature and humidity sensors (Onset® Hobologgers) in eleven commercial boar studs in five states. Large White x Landrace F1 boars (n=12; Choice Genetics®) were exposed to representative summertime conditions (heat stress, HS; 22 to 25°C) and heat wave conditions (HW; 25 to 32°C) utilizing the Brody Environmental Chambers at the University of Missouri. Neck and testicular drippers (1 gph) with and without forced air (100 cfm) were applied directly to each boar in a Latin square design with three day periods. Nooyen’s® 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® Temperature Implant): one implanted between the peritoneum and the body wall (core temperature); the other sutured between the testicular tunics (testicular temperature). Boar temperatures were analyzed using PROC MIXED (SAS 9.4). Least squares means were calculated after nonsignificant effects and interactions were removed in a stepwise fashion. The treatment most effective at creating the largest difference between treatment and control was the combination of drippers and fans on both scrotum and neck. Subsequently, this was applied to six boars (TRT) and six received no cooling (control) with all under HS. The implanted device data showed that the treatment boars had significantly lower testicular temperatures than control (32.90°C vs. 33.90°C, p-value = 0.002). However, core temperature did not vary significantly between boars. After two months boars were slaughtered and sperm collected from the epididymides of each boar. 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). Critical thresholds for each trait were identified as percentage of sample: TUNEL less than 5%, UBB less than 30%, LCA less than 10% and PNA greater than 50%. Cooling was effective at mitigating the impact of heat stress on sperm quality parameters, with a higher proportion of TRT boars meeting sperm quality targets (n TRT vs n CONTROL, 6 vs. 4 for TUNEL, 4 vs. 2 UBB, 4 vs. 2 LCA, and 4 vs. 1 for PNA respectively). Even under relatively mild thermal stress representative of commercial boar studs in the US, opportunities to improve sperm quality through cooling exist.