<b>EFFECT OF ELECTRONICALLY CONTROLLED FLOOR COOLING PADS ON THE THERMOREGULATORY RESPONSE AND REPRODUCTIVE PERFORMANCE OF DUROC BOARS DURING THE SUMMER SEASON</b>

<p dir="ltr">Heat stress causes production losses across livestock production systems. Pigs primarily thermoregulate by increasing respiration rates. As environmental temperatures rise, there is less heat loss because of temperature differences between the ambient temperature and the pig’s temperature, causing their core body temperature to rise. In boars, increased core body temperature causes increases in morphologically abnormal sperm cells and reduced motility. Producers try to mitigate heat stress with different methods of cooling. In a survey conducted by Johnson and Stewart (2025), 66.5% of the producers use fans and evaporative cool cells in a tunnel ventilated facility for breeding pigs. More advanced methods are available and gaining popularity like air conditioning and electronically-controlled floor cooling pads. Research conducted with sows and boars indicates the effectiveness of the electronically-controlled floor cooling pads (ECP) to alleviate the effects of heat stress. Research with ECPs has been limited in boars using controlled environmental temperatures with few animals. Therefore, the objective of this research was to evaluate the effects of two different versions of ECP in boars during the summer months in commercial boar studs in the U.S. </p><p dir="ltr">Chapter 2 evaluated the effects of using ECPs on boar physiological characteristics and semen production during the summer season in a boar stud in Scottsville, Kentucky. Sixty boars (461.7 ± 24.05 days old) were placed in two rows of stalls (2.06 x 0.66 m) in a 360 head tunnel ventilated cool cell boar barn near the exhaust fan end of the barn and randomly assigned to either CONTROL (n = 30; no ECP) or ECP (n = 30) treatments. Five ECPs were connected to each other and 5.1L of cold water was flushed through all the 5 ECPs. Temperature sensors were located either on the first (zone 1, 2, 4 and 5) or on the last (5th; zone 6) ECP. The flush valve opened to flush cold water when pad temperature sensors reached 27℃ for sensors placed on 5th pad and 24°C for sensors placed on 1st pad or every 4 minutes (zone 3) whichever occurs first. Boars experienced natural summer heat stress (daily temperature, humidity and dewpoint: Mean = 24.03°C, 87.9%, 21.7°C, hourly mean high = 28.9°C, 83.4%, 25.8°C). Intensive data were collected for 4 weeks from July 15, 2023, to August 14, 2023 wherein the ECP pads remained on and were flushing based on the set points. The ECP pads continued to operate through week 10, then they were removed, and semen parameters were monitored for an additional 10-week post removal. During the intensive data collection period, respiratory rate (RR) and rectal temperature (RT) were collected daily during the hottest part of the day (13:00-16:00) via counting chest or belly rises and using a rectal thermometer. Feed refusal (FR) was collected during the first 4 weeks via observing the amount of feed that was left in the feed trough at the end of the day (1500h). Semen was collected from each boar at least once a week and analyzed for motility using a CASA system, volume using a gram scale, concentration using a spectrophotometer and detailed sperm morphology using stained smear. Environmental data as well as cooling pad data were also collected. Data were analyzed using PROC MIXED for repeated measures in SAS (v.9.4). Physiological parameter analyses included the fixed effects of ECP treatment, zone within the barn, boar age class [young (< 12 months; 53%); old (≥ 12 months; 47%)], and their interactions, with day in the week included as a random effect and week as repeated measures. Semen parameter analyses included the main effects of ECP treatment, age class, days-rest between collections, zone within the barn, and their interactions, with week as a repeated measure. Boars in the ECP treatment had lower RR and RT compared to CONTROL boars (P < 0.001). The overall RR and RT for boars on ECP (daily mean = 15.4 ± 2.4 breaths/minute, 38.0 ± 0.06°C) were lower (P = 0.027 and P = 0.005 respectively) and more stable compared to CONTROL (daily mean = 42.5± 2.4 breaths/minute, 38.4 ± 0.06°C). FR was lower (P = 0.021) for ECP boars (0.01 ± 0.01 kg) than CONTROL boars (0.06 ± 0.01) and old CONTROL boars had higher (P = 0.028; +0.09 kg/day) FR than young CONTROL boars. There were no differences between CONTROL and ECP boars for majority of semen production measures (P > 0.05) for the first 10 weeks (functional ECP) and 2nd 10 weeks of analysis (no functional ECP). ECP boars had a tendency to have greater morphologically normal sperm (4.1%) compared to CONTROL boars using Hancock stain (P = 0.085). Over-all ejaculate discard rate was lower (P < 0.0001) for ECP boars (10.1 ± 0.11) compared to CONTROL boars (20.2 ± 0.15) for the first 10 weeks. CONTROL boars had higher (P < 0.05; + 23.8%) ejaculate discard rate on weeks 5 (P = 0.003; +23.8%), 7 (P = 0.008; +17.4%), 8 (P < 0.001; +30.2%) compared to ECP boars. Semen performance was reversed during the 2nd 10 weeks after the ECP were removed where ECP boars had higher ejaculate discard rates on week 11 (P < 0.075; +16.6%) and week 20 (P < 0.023; +22.4%). Overall, maintaining boars on floor cooling pads during the summer months minimized physiological indicators of heat stress, had minimal impacts on semen production, and reduced the presence of morphologically abnormal sperm which resulted in lower ejaculate discard rates. </p><p dir="ltr">A second study was conducted (Chapter 3) to evaluate the effects of using enhanced design of the ECP on boar physiology and semen quality during the summer season in a boar stud in Williamston, North Carolina. One hundred twenty boars (313 ± 130 days of age) were placed in five zones (24 stalls/zone, 2.29 x 0.66 m) across two tunnel ventilated cool cell barns (244 and 148 boars) and randomly assigned to either CONTROL (n = 60; partially slated concrete floor with no ECP) or ECP (n = 60) treatments. Cold water was continuously flushed through the individual ECPs at a flow rate of 9.1 L/min. Cold water was circulated when the temperature sensor, placed on the first outlet pipe for each zone, reached 25.0°C and the controller redirected the system to recirculate the water in the pipes when outlet water temperature was at 24.5°C. Boars were exposed to natural heat stress (daily mean temperature and humidity: 25.7°C; 97.99% and hourly mean peak 29.5°C; 100%, respectively) in a period of 90 days from July 4 to October 2, 2024. Respiration rate (RR) was taken once daily and rectal temperature (RT) was taken every other day for each barn (barn A: Monday, Wednesday, Friday; barn B-Tuesday, Thursday, Saturday) during the hottest part of the day (13:00-17:00h). Semen was collected at least once a week/boar. Semen was analyzed using MetroSperm for concentration, gram scale for volume, and subjective analysis by trained technicians for motility and morphology. Detailed morphology was completed via a stained sample and classifying 50 sperm cells if normality. Data were analyzed using PROC MIXED for repeated measures in SAS (v.9.4) with the main effects of treatment, barn, boar ID, week and their interactions, using boar age class (old/young) and zone (location in barn) as covariates for RR and RT. The model for semen quality traits included the main effects of treatment, barn, boar ID, week, age classification, and their interactions, and rest interval and barn zone as covariates. Both RR and RT were decreased by ECP (P < 0.001), and differences between ECP and CONTROL were higher (P < 0.001) in weeks where higher temperatures were recorded (week 1 avg = +4.1 breaths/min; +0.3°C; week 5 avg = +7.4 breaths/min; +0.3°C) The zone in the barn across different weeks and treatments also affected RR (P < 0.001) where the RRs for CONTROL boars in the zones near the exhaust fans was greater (zone 3 mean = 23.2 breaths/min; zone 5 mean 20.6 breaths/min) than for boars in zones near the cool cells (zone 1 mean = 16.7 breaths/min; zone 4 mean = 15.5 breaths/min). The RRs for ECP boars remained at an average range of 12.8-16.2 breaths/min for the five zones. The increase in RR in the zones farthest from cool cells was likely the result from a 0.88°C to 1.52°C greater environmental temperatures than the other zones. </p><p dir="ltr">There were no differences in semen quality estimates between CONTROL and ECP boars (P > 0.05) with the exception of ejaculate discard rate where CONTROL boars had a tendency (P = 0.090 to have higher discard rate (+1.7% discarded ejaculate) compared to ECP. Treatment by week interactions (P < 0.05) were significant with ECP boars having greater motility, total normal sperm, and detailed normal sperm with a tendency for greater total motile sperm, and normal morphology on weeks 7 and 10. Semen volume and consequently total sperm were lower for young boars compared to old boars. Motility, normal morphology and detailed normal morphology were higher for young boars than old boars. This resulted in a greater discard rate for older boars compared to younger boars. Overall, ECP use during the summer months improved the physiological indicators of heat exposure while having slight improvements in semen quality over the 90 days of study. </p><p dir="ltr">In conclusion, the two versions of ECP used in the trials in commercial boar studs effectively reduced respiration rate and rectal temperatures in boars. Greater reductions in respiration rate and rectal temperatures were observed in zones near the exhaust fans compared to zones near the air inlet cool cells. Feed refusal was greater for boars in regular stalls while it remained low for boars with ECP. There were minimal effects on semen quality for both trials with greater effects seen in the morphologically normal sperm cells and ejaculate discard rates. In both studies boars had been exposed to increased environmental temperatures for weeks prior to study initiation. This may have affected the results of these two trials in that boars can acclimate to their environment which may mask some of the expected outcomes. Boar age also had an effect on the semen quality as young boars had lower volume and total sperm cells while older boars had greater morphologically abnormal sperm cells that resulted in higher ejaculate discard rates. Colder surfaces were also noted on ECP surfaces compared to concrete surfaces while no effects were observed on leg lesions of boars regardless of treatment. The concrete floor surfaces were cleaner than the ECP surface especially for young boars. Future designs should be modified to ensure that feces and urine can better drain from the ECP surface. Collectively, the two studies support the need for further research on timing of operation, location in the barn, and improvement of the design to further enhance the effectiveness of the ECP in reducing negative effects of heat stress.</p>