Evaluation of sow thermal preference across three stages of reproduction

Abstract

The metabolic heat production of modern pigs has increased by an average of 16%, compared with sows of 30 years ago. Therefore, it is likely that temperature recommendations require updating to meet the needs of modern pigs. The objective of this study was to evaluate whether different reproductive stages of sows altered thermal preference and if current recommendations required updating. Twenty multiparous sows (3.4 ± 1.2 parity) in different reproductive stages (nonpregnant: n = 7; mid-gestation: 58.5 ± 5.68 d, n = 6; and late-gestation: 104.7 ± 2.8 d, n = 7) were tested. Thermal preference was individually tested, and sows could freely choose a temperature, using a thermal gradient between 10.4 and 30.5 °C. Sows were given 24 h to acclimate to the thermal apparatus. Before testing began, sows were given daily feed allotment and returned to the apparatus. Video from the 24-h test period was used to record sow behavior (time spent inactive), posture (upright and sternal and lateral lying), and location using instantaneous scan samples every 15 min. Data were analyzed using PROC MIXED procedure in SAS 9.4. A cubic regression model was used to calculate the sow's most preferred temperature based on the location, or temperature, in which they spent the most time. The preference range was calculated using peak temperature preference ±SE for each sow. The reproductive stage altered where sows spent their time within the thermal gradient (P < 0.01). Late-gestation sows preferred cooler temperatures (14.0 °C) than mid-gestation (14.8 °C; P < 0.01) and nonpregnant sows (14.8 °C; P < 0.01). In summary, sow thermal preferences were within the lower half of the current recommended range (10 to 25 °C). This indicates that temperatures at the higher end of the recommended range could be uncomfortable to sows and that the thermal comfort zone of sows may be narrower than recommendations indicate.

Keywords: reproductive stage; sows; thermal comfort zone; thermal preference; thermal recommendations.

Figure 1.

Top view of a single thermal apparatus showing average temperature per thermal zone.

Figure 2.

Percentage of observations in different temperatures within the thermal gradient based on the reproduction stage and during inactive behaviors. The effects of the reproductive stage (nonpregnant; mid-gestation: 58.5 ± 5.68 d; and late gestation: 104.7 ± 2.8 d) on thermal preference. Temperature within the thermal apparatus is plotted on the0 x-axis, and the percentage of time observed during inactive behaviors is plotted on the y-axis as a log₁₀ + 0.001 scale. Cubic peaks are indicated by vertical lines corresponding to the reproductive stage. Standard error bars are located at the temperatures of the five thermal zones (10.4, 19.2, 23.6, 27.5, and 30.5 °C); different letters denote significant Tukey pairwise comparisons (P < 0.01), and no letters given where no significance was found between the three reproductive stages. The gray box indicates the recommended temperatures (10 to 25°C) for sows or boars > 100 kg (Federation for Animal Science Societies, 2020).

Figure 3.

BW in kilograms per sow based on the number of piglets (piglets). Symbols represent individual sows.

Figure 4.

Weight in kilograms per sow and preferred peak thermal preference based on the amount of time spent within the five thermal zones (10.4, 19.2, 23.6, 27.5, and 30.5 °C) during inactivity. Symbols represent individual sow weights.

Figure 5.

Percentage of observations in different temperatures within the thermal gradient based on posture. Data are plotted by postures: lateral and sternal lying, and upright. Temperature within the thermal apparatus is plotted on the x-axis, and the percentage of time observed is plotted on the y-axis as a log₁₀ + 0.001 scale. Cubic peaks are indicated by solid vertical lines. Standard error bars are located at the temperatures of the five thermal zones (10.4, 19.2, 23.6, 27.5, and 30.5 °C). Different letters denote significant Tukey pairwise comparisons (P < 0.01). The gray box indicates the recommended temperatures (10 to 25 °C) for sows or boars > 100 kg (Federation for Animal Science Societies, 2020).