Neonatal infrared thermography images in the hypothermic ruminant model: Anatomical-morphological-physiological aspects and mechanisms for thermoregulation

Abstract

Hypothermia is one factor associated with mortality in newborn ruminants due to the drastic temperature change upon exposure to the extrauterine environment in the first hours after birth. Ruminants are precocial whose mechanisms for generating heat or preventing heat loss involve genetic characteristics, the degree of neurodevelopment at birth and environmental aspects. These elements combine to form a more efficient mechanism than those found in altricial species. Although the degree of neurodevelopment is an important advantage for these species, their greater mobility helps them to search for the udder and consume colostrum after birth. However, anatomical differences such as the distribution of adipose tissue or the presence of type II muscle fibers could lead to the understanding that these species use their energy resources more efficiently for heat production. The introduction of unconventional ruminant species, such as the water buffalo, has led to rethinking other characteristics like the skin thickness or the coat type that could intervene in the thermoregulation capacity of the newborn. Implementing tools to analyze species-specific characteristics that help prevent a critical decline in temperature is deemed a fundamental strategy for avoiding the adverse effects of a compromised thermoregulatory function. Although thermography is a non-invasive method to assess superficial temperature in several non-human animal species, in newborn ruminants there is limited information about its application, making it necessary to discuss the usefulness of this tool. This review aims to analyze the effects of hypothermia in newborn ruminants, their thermoregulation mechanisms that compensate for this condition, and the application of infrared thermography (IRT) to identify cases with hypothermia.

Keywords: cattle; goat; infrared thermography; newborn/neonate; sheep; thermoregulation; water buffalo; wild ruminants.

Figure 1

Anatomical traits of newborn ruminants. 1. supraclavicular region; 2. neck region; 3. pericardial region; 4. perirenal region; BAT, brown adipose tissue; G1P, glucose 1 phosphate; G6P, glucose 6 phosphate; NE, norepinephrine; TG, triglycerides; UCP1, uncoupling protein 1.

Figure 2

Effect of birth weight on the average temperature of water buffalo neonates (n = 50) in the first 48 h of life by evaluating six thermal windows. Data was obtained using variance analysis (ANOVA) by the mixed general linear model, with multiple comparisons of means using Holm-Sidak's test, Shapiro-Wilk normality test, and a significance level of p < 0.05. ^{a, b} Different literals indicate significant differences between groups of high- and low-weight buffalo calves (p < 0.05). Images were taken with a FLIR camera (FLIR Systems, Boston, MA, USA), 18 mm lens FOL, the emissivity of 0.95, IR resolution of 320 × 240, and a reflecting temperature of 20°C. The thermal images were processed by the software FLIR tools. (A) comparison of the mean temperature at parturition in groups with high and low birth weights, (B) comparison of the mean temperature at 24 h after parturition in groups with high and low birth weights, and (C) comparison of the mean temperature at 48 h after parturition in groups with high and low birth weights.

Figure 3

Hypothalamic response to hypothermia. Ca²⁺, calcium; DH, dorsal horn; DRG, dorsal root ganglion; IML, intermediolateral column; LPBel, external lateral part of the lateral parabrachial nucleus; MnPO, median preoptic nucleus; Na⁺, sodium; RPa, raphe pallidus. TRPA, transient receptor potential ankyrin 1; TRPC5, transient receptor potential canonical 5; TRPM8, transient receptor potential melastatin 8.

Figure 4

Peripheral responses as coping mechanisms for hypothermia. When the thermoregulatory center of the central nervous system (MnPO) perceives a decrease in body temperature, the organism of newborn ruminants (and other mammals) activates peripheral responses with two main objectives: (A) to prevent heat loss through vasoconstriction and piloerection; and (B) to produce heat by shivering and non-shivering thermogenesis, where BAT and skeletal muscle fibers participate in the return to a state of homeothermy.

Figure 5

Thermal windows in newborn water buffalo. (A) pelvic limb, (B) facial window, (B1) auditory canal, (B2) ocular region, (B3) lacrimal gland, (B4) lacrimal caruncle, and (C) nostrils.

Figure 6

Effect of age measured in hours (0–48 h) on the temperature of newborn buffaloes in different thermal windows. In all events (hours), statistically significant differences (p < 0.0001) were observed in all measured times, except on the lacrimal gland and pelvic limb windows at 24 and 48 h post-birth. The average temperature at the ear canal differed from day 0 to day 2, with the highest value at 48 h post-birth (36.5°C) and the lowest at 24 h post-birth (34.5°C). The lacrimal gland window only showed differences of an average of 0.4°C from day 0 to day 1. The temperature of the nostril window showed a tendency to drop 0.8°C from birth to 24 h post-birth and 1.2°C from 24 h to 48 h post-birth. Meanwhile, a generally lower temperature was observed in the pelvic limb at birth (29.3°C) but it rose by 5.5°C at 24 h post-birth before decreasing by 0.3°C at 48 h post-birth. Data was obtained using variance analysis (ANOVA) by the mixed general linear model, with multiple comparisons of means using Tukey's test, Shapiro-Wilk normality test, and a significance level of p < 0.05. ^{1, 2, 3} Different numerals indicate significant differences between events according to the age of the buffalo calves (p < 0.05).