Suitability of Different Thermometers for Measuring Body Core and Skin Temperatures in Suckling Piglets

Abstract

Monitoring the temperature of piglets after birth is critical to ensure their well-being. Rectal temperature measurement is time-consuming, requires fixation of the animal and is stressful for piglets. This study aims to evaluate the effectiveness of infrared thermometry and thermography as compared to rectal temperatures. We investigated digital thermometers for rectal measurements, infrared ear thermometers, infrared forehead thermometers, infrared laser thermometers and an infrared camera during field trials with piglets aged 1-13 days. Temperatures differed between the left and right ear and ear base (p < 0.01), but not between temples. Three forehead and laser devices yielded different temperatures (p < 0.01). Temperatures assessed with a laser thermometer decreased with distance from the target (p < 0.01). The highest correlation observed was between the rectal and tympanic temperatures (r = 0.89; p < 0.01). For temperatures assessed with the camera, inner thigh and abdomen correlated most closely to core temperature (0.60 ≤ r ≤ 0.62; p < 0.01). Results indicate that infrared ear thermometry commonly used in humans is also suited for assessing temperature in piglets. The inner thigh and abdomen seem promising locations for estimating core temperature with an infrared camera, but this approach needs to be adapted to reduce time exposure and stress for the piglets to be used under practical conditions.

Keywords: core temperature; infrared thermography; infrared thermometry; suckling piglet; surface temperature; tympanic membrane temperature.

Figure 1

Skin temperatures (p < 0.001) measured with 3 laser thermometers at the same measuring point at both sides of the body of piglets (n = 180) at 10 cm distance (A) and differences of temperatures (p < 0.001) measured at left and right side of the body of newborn piglets (n = 180) at 10 cm distance with the same infrared laser thermometer (B). Different letters (a, b, c) indicate significant differences.

Figure 2

Span of skin temperatures measured with distances of 10, 30, 50 or 100 cm and differences (p < 0.01) between infrared laser thermometer and piglet (n = 360). Different letters (a, b, c, d) indicate significant differences.

Figure 3

Temperature deviations as a difference between the gold standard (rectal temperatures) and temperatures assessed in-ear (A: infrared ear thermometer, n = 423), at ear base (B: infrared laser thermometer, n = 670), and at head, throat, rib, hip, inner thigh, and abdomen with an infrared camera in piglets (C: n ≥ 488). Differences were calculated per pig as absolute amounts (∆t = |t_rectal − t_x|).

Figure 4

Scatter plots (A,B) and ROC curves including the area under the curve (AUC) (C,D) showing correlations and comparing rectally measured temperature with a digital thermometer and temperatures assessed using (A,C) an infrared ear thermometer (n = 424) or (B,D) an infrared laser thermometer (n = 671) in piglets during field trials (p < 0.01).