Infrared skin temperature measurements for monitoring health in pigs: a review

Table 4 Studies that investigated the linear regression between surface (measured by infrared devices) and body temperature

Source	N	Breed	Size/Age	Surface area(s)	Thermal window (X: yes)	T _ambient [°C]	Regression ( ^A )		Remarks
Source	N	Breed	Size/Age	Surface area(s)	Thermal window (X: yes)	T _ambient [°C]	Constant, T ₀ [°C]	Coefficient, b	Remarks
Dewulf et al. [54]	12	Belgian LR	12–15 kg	Ear		~20	38.80	0.015
				Flank			37.82	0.044 (**)
				Legs (carpus and tarsus)			38.24	0.032 (**)
				Anus	X		38.02	0.038 (**)
Warriss et al. [7]	384		~91 kg	Inner side of ear pinna	X^B	21	4.93	1.12 (***)	r = 0.71 , (^C)
Chung et al. [38]	10	Yorkshire × LR (Gnoto-biotic)	Piglets	Eyelid, ear, parietal and axilla	X^B	21 ± 1			No significant relationship
				Central abdomen	X		28.07	0.304 (***)	Adj. R² = 0.34
				Central dorsum			34.03	0.152 (***)	Adj. R² = 0.09
				Perianal region	X		33.88	0.157 (***)	Adj. R² = 0.19
Kammersgaard et al. [55]	91	(LR × Yorkshire) × Duroc	1–48 hours	Entire piglet from dorsal view and sagittal view	X^B	15, 20, and 25	14.72	0.63 (***)	Avg. of max. IR pixel temp. from dorsal view and sagittal view

^ARegression formula: T_body = T₀ + b*T_skin. Body temperature measurement site was the rectum if not otherwise mentioned. **:P < 0.01 and ***:P < 0.001.
^BIndicates measurement sites that are both thermal windows and not thermal windows.
^CTemperature was the mean of the 3 spots of the ear (base, middle, and tip). Body temperature was measured by aiming IR spotmeter on blood on concrete floor, lost from sticking neck vessels.

ISSN: 1751-0147