An accurate understanding of boar temperature preferences may allow the swine industry to design and utilize environmental control systems in boar facilities more precisely. Therefore, the study objective was to determine the temperature preferences of sexually mature Duroc, Landrace, and Yorkshire boars. Eighteen, 8.57 ± 0.10-mo-old boars (N = 6 Duroc, 6 Landrace, and 6 Yorkshire; 186.25 ± 2.25 kg) were individually tested in thermal apparatuses (12.20 m × 1.52 m × 1.86 m) that allowed free choice of their preferred temperature within a 8.92 to 27.92 ºC range. For analyses, the apparatuses were divided into five thermal zones (3.71 m2/thermal zone) with temperature recorded 1.17 m above the floor in the middle of each zone. Target temperatures for thermal zones 1 to 5 were 10, 15, 20, 25, and 30 ºC, respectively. All boars were given a 24-h acclimation phase followed by a 24-h testing phase within the thermal apparatuses. Daily feed allotments (3.63 kg/d) were provided to each boar and all boars were allowed to consume all feed prior to entering the thermal apparatus. Water was provided ad libitum within the thermal apparatuses with 1 waterer per thermal zone. During testing, boars were video recorded continuously to evaluate behavior (inactive, active, or other), posture (lying, standing, or other), and thermal zone the boar occupied. All parameters were recorded in 15 min intervals using instantaneous scan sampling. Data were analyzed using GLM in JMP 15. For the analyses, only time spent lying or inactive were used because they were observed most frequently (lying 80.02%, inactive 77.64%) and were deemed to be associated with comfort based on previous research. Percent time spent active (19.73%) or standing (15.87%) were associated with latrine or drinking activity and were too low to accurately analyze as an indicator of thermal preference. Breed did not affect temperature preference (P > 0.05). A cubic regression model determined that boars spent the majority of their time inactive at 25.50 ºC (P < 0.01) and lying (both sternal and lateral) at 25.90 ºC (P < 0.01). These data suggest that boar thermal preferences did not differ by breed and that boars prefer temperatures at the upper end of current guidelines (10.00 to 25.00 ºC).
Keywords: behavior; boars; thermal comfort zone; thermal preference; thermal recommendations.
Published by Oxford University Press for the American Society of Animal Science 2023.