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J Anim Behav Biometeorol (2021) 9:2112
REVIEW ARTICLE
Published Online: January 27, 2021
https://doi.org/10.31893/jabb.21012
Received: November 16, 2020 | Accepted: December 07, 2020
Thermal homeostasis in the newborn puppy:
behavioral and physiological responses
Brenda Reyes-Soteloa | Daniel Mota-Rojas b*| Julio Martínez-Burnesc |
Adriana Olmos-Hernándezd| Ismael Hernández-Ávalose| Nancy Joséb |
Alejandro Casas-Alvaradob | Jocelyn Gómezb | Patricia Mora-Medinaf
aMaster in Science Program “Maestría en Ciencias Agropecuarias”, Universidad Autónoma Metropolitana, Xochimilco Campus, Mexico City, Mexico .
bNeurophysiology, Behavior and Animal Welfare Assessment, DPAA, Universidad Autónoma Metro politana (UAM), Mexico City, Mexico.
cGraduate and Research Department, Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Tamaulipas, Victoria City, Tamaulipas, Mexico.
dDivision of Biotechnology—Bioterio and Experimental Surgery, Instituto Nacional de Rehabilitación‐Luis Guillermo Ibarra Ibarra (INR‐LGII), Secretaría de Salud
(SSA), Mexico City, Mexico.
eClinical Pharmacology and Veterinary Anaesthesia, Department of Biological Science, FESC, Universidad Nacional Autónoma de México (UNAM), Mexico.
fDepartment of Livestock Sciences. Universidad Nacional Autónoma de México (UNAM), FESC, Mexico.
*Corresponding author: dmota@correo.xoc.uam.mx
1. Introduction
Mortality in the newborn puppy ranges from 5 to 35%,
and one of the leading causes is hypothermia (Münnich and
Küchenmeister 2014), although its incidence is not reported
and then is not well known. Therefore, thermoregulation
becomes essential in the newborn puppy because it is
deficient (Fitzgerald and Newquist 2011; Hull 1973); thus, the
processes like hypothermia and hyperthermia develop fast
(Harri et al 1991). Neonatal survival is tightly related to
thermogenesis, especially when there is a significant
reduction of the body temperature at the time of birth when
passing from a warm environment in the uterus to an
extrauterine environment (Nowak and Poindron 2006;
Vannucchi et al. 2012); a change that impacts the newborn
puppy because it lacks the shivering reflex and the
vasoconstriction mechanisms, which are still under
development (Indrebø et al. 2007; Nakamura and Morrison
2011).
The first 24 to 72 h after birth comprise the highest risk
time for the temperature descent (Mullany et al. 2010), which
can lead to systemic biochemical changes, such as
hypoglycemia, hypoalbuminemia, energy alteration, that can
trigger a delay in growth, an acid-base alteration, leading to
multiple organ dysfunction (Lawler 2008). The ingestion of
the colostrum could provide a 10% weight recovery during
the first 24 h after birthand ensure the newborn puppy’s
survival.
On the other hand, there is scientific interest in the
appropriate use of therapeutic hypothermia for pathological
processes mainly in humans and, recently, in veterinary
medicine (Brodeur et al 2017). This therapy is based on the
reduction of the metabolic demand of the central nervous
system (SNC) (Polderman 2009; Sinclair and Andrews 2010).
For this reason, the objectives of this review are: to analyze
the factors that affect the thermoregulation of the newborn
puppy, its behavioral and physiological responses, to discuss
the influence of the colostrum as an energy source and for the
production of heat in the face of hypothermia, and to
consider the recent scientific findings from the use of infrared
thermography (IRT) to assess the thermal response to cope
with hypothermia in the newborn puppy.
2. Physiological response to hypothermia
Thermoregulation in newborn mammals, both human
and non-human, is deficient as compared to that of adults
(Fitzgerald and Newquist 2011; Hull 1973; Mota-Rojas et al.
Abstract Adaptation to extrauterine life brings about various changes, which initially are reflected in physiological
alterations in the newborn puppy. Also, the newborn puppy's thermoregulating capacity is deficient, and many of the
physiological processes for survival depend on this capacity. Severe modifications in body temperature can lead to
hypothermia in a few hours. Hence, the first 24 to 72 h of life correspond to the highest risk time, in which the newborn can
course with moderate to severe hypothermia because the shivering reflexes and vasoconstriction mechanisms are not yet
developed in the newborn of this species. Temperature stabilization is reached up to the 18th day of age. However, the
colostrum's adequate consumption could provide a high energy supply, contributing to a fast recovery of temperature and,
consequently, to a high survival rate. This review aims to analyze the factors that affect thermoregulation of the newborn
puppy, the physiological and behavioral responses, as well as to discuss the influence of the colostrum as an energy source
and production of heat to face hypothermia, aside from discussing recent scientific findings of infrared thermography (IRT)
used to assess the thermal response of the newborn puppy to cope with hypothermia.
Keywords cooling, hypothermia, neonatal care, puppy welfare, thermal biology, viability
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2016, 2018; Bertoni et al. 2019; Casas-Alvarado et al. 2020)
because the thermoneutral zone is narrow and depends on
the type of stimulus for the processes of hypothermia and
hyperthermia to develop (Harri et al. 1991; Mota-Rojas et al.
2019a,b; 2020; 2021a,b; Bertoni et al. 2020a,b).
Temperatures below 36.5ºC are associated with hypothermia
and an increase in mortality (Chitty and Wyllie 2013; Laptook
et al. 2007; Martínez-Burnes et al. 2019; Villanueva-García et
al 2021).
The newborn’s normal rectal temperature ranges
between 35 and 37°C, increasing from 36.1°C to 37.8°C on the
first day of age and reaching a self-regulation period on day
28 after birth (Wilborn 2018). However, just after birth,
temperature diminishes, perhaps, as an adaptation measure,
protecting against hypoxia and acidosis, reducing the
metabolic demand (Lawler 2008; van der Weyden et al.
1986). It is then that hypothermia produces a decrease in the
metabolic activity of tissues, like the central nervous system
(SNC), with the subsequent diminution of the ionic exchange
needs and, hence, of adenosine triphosphate (ATP)
consumption. This reduction in the mitochondrial activity and
the binding of decoupling proteins reduces the generation of
reactive species without losing the transmembrane
potentials and blocking the release of apoptogenic proteins
(Lehtonen et al. 2017; Nuñez et al. 2018).
It must also be considered that the physiological
functions are kept within the average temperature; however,
if body temperature descends to 21.1ºC, a drastic reduction
of the cardiac rhythm to 40 beats per minute (bpm) and loss
of the suction reflex can be observed (Fitzgerald and
Newquist 2011). In turn, hypothermia is associated with an
increase in the metabolic rate (Gandy et al. 1964), respiratory
distress (Costeloe et al. 2012; Stephenson et al. 1970),
diminished ingestion of colostrums, and low weight gain
(Glass et al 1968), hypoglycemia (Lenclen et al. 2002; Mann
and Elliott 1957; Mathur et al. 2005), and alterations of the
acid-base equilibrium (Gandy et al. 1964); all changes lead to
a multiple organ failure (Lawler 2008; Mota-Rojas et al.
2019a,b; 2020; 2021a,b).
Therefore, the first 24 to 72 h represent a higher risk
of suffering moderate to severe hypothermia (Mullany et al.
2010). In lambs, Vannucchi et al. (2012) demonstrated that
they can regulate their temperature during the first 60 min
after birth, in contrast to calves and puppies. Thus, neonatal
survival is related to thermogenesis (Mota-Rojas 1996, Mota-
Rojas and Ramírez-Necoechea 1996; Nowak and Poindron,
2006; Vannucchi et al. 2012).
For these reasons, it is essential to maintain a
controlled environmental temperature for the newborn
puppy and provide an adequate temperature during the first
week of life to prevent hypothermia. Also, avoid overheating
which can trigger a dehydration process by respiratory failure
due to reduced ventilatory response to carbon dioxide.
3. Behavioral response to hypothermia
All neonates can reduce their heat loss through
behavioral adjustments like keeping together, searching for
warm places, responding to the mother’s call when they
perceive cold, and maintaining quiet while being heated
(Harri et al 1991; Hull 1973; Mota-Rojas et al 2016; 2018). The
mother will separate the stillborn from the nest (Harri et al
1991). In altricial species, like the dog, which is immature at
birth, stabilization of temperature is not reached until day 18
of age (Pineda and Dooley 2008).
In dog neonates, the shivering reflexes and the
vasoconstriction mechanisms are not developed; hence, they
are inefficient to compensate for the heat loss (Indrebø et al.
2007). However, if the temperature is in the thermoneutral
zone, they will not vocalize and keep quiet or sleeping, as
occurs in other species when perceiving a warm temperature
(Welker 1959; Harri et al. 1991). In contrast, in cold
environments, it has been observed that blue fox puppies
tend to minimize heat loss through behavioral responses,
maximizing the production of heat (metabolism). Heat is
produced by metabolism, but its increase leads to a loss by
increasing circulation, which generates heat transfer from
the inside to the surface, triggering a more significant heat
loss than that produced, leading to a faster cooling (Harri et
al. 1991).
For the dog, it has been argued that the adopted
mechanism is the same because thermogenesis with
shivering is low or absent, as can be observed in Figure 1,
resulting in a higher predisposition to develop hypothermia.
Dog puppies have only 1.3% of body fat (Kienzle et al. 1998);
hence, it could be that they primarily use the production of
heat using non-shivering thermogenesis; thus, eating could
be their only option for thermogenesis (Mila et al. 2015).
The puppy develops both behavioral and physiological
strategies to avoid losing heat or, if already lost, to generate
heat. Among the behavioral responses is the development of
postures like the ball-like posture and huddling with
congeners to reduce the body surface exposure to the
environment and, keep body heat. Among the behavioral
strategies developed to produce body-heat are increased
energetic food consumption (Terrien et al. 2011). Regarding
the physiological strategies, the puppy can start peripheral
vasoconstriction and thermogenesis responses with or
without shivering, although it has been described that
puppies can only execute this response at 6 to 8 days of age
(Lourenço and Machado 2013).
4. Factors that influence thermoregulation in the newborn
Diverse factors can be related to the thermoregulation
of the newborn; in humans, for example, the maturation of
the skin, the presence, and distribution of subcutaneous fat,
genetic, ethnic, and metabolic factors can affect the thermal
balance in a specific way in premature babies (Heimann et al
2013). In contrast, in mammals, like the dog, Johnson et al
(2006) observed that the hair plays an essential role
according to its consistency; thin hair diminishes the loss of
heat from the skin, whereas the color of the hair, in the case
of dark colors, tends to absorb more heat. In contrast, dogs
with poor hair or absence have a lower capacity to retain heat
or tolerate cold temperatures. It must be noted that smaller
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dogs tend to lose heat faster due to greater surface area to
volume ratios (Rigotti et al 2015). For this reason, the
temperature of the environment where the puppies are
housed can have a negative or positive effect on their
wellbeing (Jordan et al 2016); moisture, for example, must be
kept at levels between 30 and 70% but maintaining sufficient
ventilation to reduce foul smells, high ammonia levels,
controlled air currents and moisture condensation (USDA
2013).
Figure 1 Routes to avoid heat loss in the newborn puppy.
Figure 2 depicts the remainder factors that influence
the thermoregulation of the newborn puppy.
Among the factors that influence the
thermoregulation of the puppy are the consumption of
colostrum, the body weight at birth, the environmental
temperature, and even the breed; the body weight and the
growth rate are important variables for the progressive
increase of body temperature in puppies (Piccione et al
2010).
On the other side, Piccione et al (2009) observed that
the daily oscillation of body temperature is weaker in the
newborn and increases as the animal grows. This also
changes according to the breed. These authors included 19
breeds; none of them exhibited significant temperature
rhythmicity after birth, which reached a stable level at 6
weeks of age. Additionally, the difference between the
morning and evening temperatures was noted for the first
time on day 9 and increased gradually until reaching a stable
daily rhythm at about 8 weeks after birth (Piccione et al
2010).
4.1. Heat loss due to evaporation in the wet newborn puppy
Dog neonates have a lower temperature than adults;
in the first week of life, the rectal temperature ranges
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between 35 and 36ºC, reaching 36-38ºC in the following
weeks and, finally, at the time of weaning, temperatures
become equal to that of adult dogs (Fitzgerald and Newquist
2011). The thermoregulating capacity is deficient, and the
newborn’s heat losses occur through conduction, convection,
evaporation, and radiation processes (Knobel-Dail et al
2017), as can be observed in Figure 3. The most frequent are
convection and evaporation, leading to heat production and
developing peripheral vasoconstriction to avoid more heat
loss (Adamson and Towell 1965).
After birth, puppies face a lower environmental
temperature than that prevailing in the intrauterine
environment and start losing heat through evaporation,
conduction, radiation, and convection. The heat loss through
evaporation occurs due to amniotic fluid on the newborns’
surface; besides being in contact with cold surfaces, like
metal tables, they lose heat through conduction. Newborn
puppies also lose heat through radiation by emitting heat in
electromagnetic waves, especially if they are in a cold
environment. Likewise, moisture and wind produce heat loss
through convection (Smith 2012).
In adult dogs, heat loss by evaporation through
panting is the most important (Sessler 2000). Together with
this, the coating acts as an isolator trapping the air against
the skin because the latter possesses a low thermal
conductivity (Randall et al 2002). However, in the case of wet
coats, this isolation process is not efficient because water by
having a high thermal conductivity leads to the development
of more hypothermia, together with other factors, such as
the diminished body fat, age, disease, or lack of acclimation
(Mallet 2002; Oncken et al 2001; Sugano 1981), as occurs in
newborns when diminishing their heat production
(Armstrong et al 2005).
In a preliminary study of eutocic and dystocic
deliveries in dogs, published by the authors of this work, the
temperatures were recorded in diverse body regions in the
wet puppy immediately after birth, observing differences
among them; despite being wet, the puppy presents high
temperatures due to the heat kept by the amniotic fluid that
covers it, as can be seen in Figure 4.
For this reason, drying the newborn immediately after
birth is basic and elemental in the handling of the newborn,
reducing the heat losses due to evaporation, and providing
controlled environmental conditions to promote a better
adaptation and reducing mortality.
Figure 2 Factors that influence the thermoregulation of the newborn puppy.
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Figure 3 External mechanisms of heat loss in the newborn puppy.
Figure 4 Changes in the vascular microcirculation observed with infrared thermography (IRT) in the newborn puppy wet with amniotic fluid,
without colostrum, identified in different body regions. A) Forelimb (thoracic member). (El1) possess a minimal temperature of 30.7 °C and
maximal 32.4 °C. Hind limb (Pelvic member) (El2) with a minimum temperature of 32.4 °C and a maximal of 33.4 °C, which are 1.7 °C and 1
°C higher than those of the thoracic extremities. Umbilical cord insertion (E13) indicates a minimal temperature of 30.4 °C and a maximal of
34.2 °C; the umbilical cord has not been clamped yet. B) Thoracic region (Bx1) shows a minimal temperature of 32.9 °C and maximal of 34.4
°C, which are just below the minimal normal rectal temperature of the newborn puppy (35 °C). Abdominal region (Bx2) reveals a minimal
temperature of 33.7 °C and maximal of 35.6 °C; being 0.8ºC and 1.2 °C higher in this region than in the thoracic region.
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4.2. The relation between hypothermia and vitality of the
puppy
The degree and distribution of postnatal hypothermia
are negatively correlated with survival (Tuchscherer et al
2000). In human medicine, the Apgar system, used since the
’50s, assesses the neonatal viability level at 5 min after birth
(Finster and Wood 2005) and is used as a predictor of
mortality (Casey et al 2001). This system in veterinary
medicine has been adapted to the characteristics of diverse
species, foal, calf, piglets, and, recently, puppies. The five
parameters to evaluate vitality in the newborn puppy are the
color of mucosal membrane, cardiac rhythm, irritability
reflex, mobility, respiratory frequency, obtaining from 0 to 2
points to reach a total of 10 points. It has been demonstrated
that scores below 6 total points, when monitoring during the
first 5 min of life, result in increased mortality indices in the
first 24 h of life (Veronesi et al 2009). Currently it is known to
be useful in the determination of mortality during the first 8
h of life, as demonstrated by Mila et al (2017), they assessed
367 newborn puppies from 66 different-sized bitches, the
observation covered from 10 min to 8 h post-birth recordings
of the Apgar score, glucose, lactate, beta-hydroxybutyrate,
rectal temperature, and urinary gravity. A second recording
was performed at 24 h after that, except for Apgar score and
weight. Finally, mortality from birth to 21 days of age was
monitored. They found that the Apgar score was influenced
by the weight at birth (P < 0.001) and that during the first 24
h, only glucose could be associated with high mortality risk (P
< 0.001). It should be noted that the increase in weight was
associated with an increase in rectal temperature on the first
day of birth (P < 0.001). A possible explanation is that an
insufficient brown adipose tissue (BAT) originates a fast
decrement of glucagon and limited hepatic activity.
Therefore, being the ingestion of the colostrum the only
energy source leads to the diminution of temperature, which
in turn, will be responsible for causing a low suction that will
reflect in reduced ingestion of colostrum and, in
consequence, of energy, with the possible risk of septicemia
(Münnich and Küchenmeister 2014). For this reason,
Groppetti et al (2010) consider evaluating suction and
vocalization as additional parameters.
It is important to emphasize that the vitality scale
differs in the canine species, due to brachycephalic breeds.
However, the Apgar score is a method that allows evaluating
the newborn puppy in the first minutes of life, and helps to
identify those puppies that might require emergency medical
care.
4.3. Weight at birth (muscle mass and glycogen energy
reserves)
Bodyweight is one of the most important factors that
influence cooling down, as observed in foxes, where the body
mass index (BMI) determined the thermoregulating capacity
of the offspring (Harri et al 1991). However, it must be taken
into account that the weight at birth is correlated with the
maternal weight and represents in average between 1 and
3% of the body weight of the bitch (Trangerud et al 2007);
likewise, the size of the clutch is associated with a low birth
weight (Mila et al 2015). Indrebø et al (2007) observed, in 744
puppies, that low birth weight and agalactia were the most
frequent causes of death during the first 3 days after birth.
Therefore, the bodyweight daily recording allows monitoring
the average 8% increase during the first 3 days and 12%
during the following 4 days.
For these reasons, maintaining a temperature and
adequate glucose levels is limited in the newborn puppy
(Allen et al 1966). Hence, hypothermia and hypoglycemia can
trigger fatal consequences (Münnich and Küchenmeister
2014). Because neonates are unable to use the glycogen
reserves and cannot maintain adequate levels of glucose in
blood without constant feeding; it is so, that competing with
its clutch for the nipple or colostrum at birth can bring about
serious repercussions, initially of dehydration (Wilborn 2018)
that later on will impact the neonatal survival (Groppetti et al
2015; Schrack et al 2017).
Some peripartum complications that predispose to
hypoglycemia are a placental failure, premature birth,
hypoxia, hypogalactia or agalactia, and adverse
environmental conditions (Lawler, 2008). Hence, glucose and
lack of oxygen lead to a fast deterioration of the energetic
reserves and, in a short time, to tissue death (Nuñez et al
2018).
4.4. Colostrum intake
Animals that are born healthy develop the suction
reflex within the first hour of life; hence, the colostrum intake
provides the newborn not only a recovery of 10% of the lost
body during the first 24 h after birth but also immunity during
the first weeks and, aside from adequate nutrition, it enables
the puppy to produce heat (Fitzgerald and Newquist 2011).
Although, according to Kammersgaard et al (2011), the first
suction only stimulates the displacement capacity of
newborn piglets to reach a good position for nursing during
the first two hours after birth, and thermoregulation is not
entirely successful in this period. In the newborn puppy,
colostrum effects can be observed in Figure 5, assessed from
the moment of birth until 60 min post-colostrum, using
different thermal windows.
In turn, Mila et al (2014) observed a total of 532
newborn puppies from 100 bitches in a controlled
temperature (28 and 30 °C) environment at the floor level
and without any other intervention. They determined that
the birth weight is not correlated with mortality between day
2 and day 21 of age, but rather with the growth rhythm,
which is due to the adequate ingestion of colostrum and its
supply (First Day of lactation: 548kJ/100g and
immunoglobulin G (IgG): 19.4G/L). They stated that adequate
ingestion of colostrum provides the newborn a high supply of
energy, which contributes to a fast recovery of the
temperature lost at the time of birth and, concomitantly, its
immature thermoregulation to avoid hypothermia (Dwyer
and Morgan 2006). The colostrum supply contributes to the
correct maturation and function of the gastrointestinal
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system, including nutrients absorption, as demonstrated in
dogs, pigs, and calves (Bühler et al 1998; Burrin et al 1992;
Schwarz and Heird 1994), diminishing the mortality indices.
However, the newborn puppy can have difficulties
localizing the breast, leading to a delayed colostrum intake
(Arteaga et al 2013). Hence, as demonstrated by Reyes-
Sotelo (2020), once the newborn has nursed on colostrum,
monitoring the different body regions is of vital importance
to ensure temperature recovery by the newborn because, as
shown in Figure 6, at 5 min post-colostrum, low temperatures
are still observed, which require the establishment of
protocols to increase the temperature of the puppy. Based
on the aforementioned, Lawler (2008) suggests specific
measures that will ensure the colostrum intake, such as
reducing the excessive noise and maternal activity, help the
puppy to nurse colostrum several times per day, maintain an
adequate environmental temperature in the maternity areas
or wherever the bitch gave birth, as well as favorable hygiene
conditions, monitoring the weight gain of the newborn and
its activity.
Figure 5 The maximal, minimal, and average temperature of the newborn puppy’s thermal windows under four stages: wet, dry, post-
colostrum, and 60 min post-colostrum. A) Temperature expressed in the Periocular region, indicates a minimum temperature of 23.7 °C and
a marked increase of 0.47 °C (24.17 °C). B) Upper lid. Note the temperature’s behavior, the wet newborn evidence a minimal temperature of
32.9 °C, which tends to diminish 2.13 °C when dry; after that, the puppy raises the temperature to 1.15 °C during the post-colostrum stage,
and tends to diminish 0.5 °C during the 60-min post-colostrum. C) Lower lid. Observe the temperature in the wet puppy (24.2 °C), which
continues to diminish 2.1 °C when being dry; it increases 0.4 °C in the post-colostrum stage and keeps increasing up to 1.1 °C at 60 min post-
colostrum. D) Thorax. The minimal temperature expressed by remaining wet is of 21.9 °C, it increases slightly in 0.34 °C when dry, and
diminishes 0.39 °C in the post-colostrum; at 60 min post-colostrum, the temperature increases consecutively exceeding even the temperature
exhibited while being wet (23.27 vs. 22.6 °C). E) Abdomen. It exhibits a minimum temperature of 21.9 °C by remaining wet, 22.05 °C when
dry, followed by 21.9 °C at post-colostrum, and an evident 1.12 °C increase at 60 min post-colostrum. F) Fore limb (thoracic member). It
expresses a minimal temperature of 22.6 °C when wet, maintaining a temperature of 22.27 °C and 22.5 °C when dry and post-colostrum,
respectively, which increases 0.77 °C at 60 min post-colostrum. G) Hind limb (Pelvic member). Note the 0.8 °C descent in the minimal
temperature from wet to dry, keeping a temperature of 20.9 °C post-colostrum; its temperature continues increases almost 1 °C (i.e., 0.95 °C).
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Figure 6 Effect of colostrum (5 min post-colostrum) on the dry newborn puppy’s microcirculatory thermal changes in four different body
regions. A) Ear canal (ellipse El1). Presents an average temperature of 23.4 °C. Periocular region limited by an ellipse (El2), the recording is
on average of 23.5 °C; hence, compared with the auditory canal, there is a 0.1 °C ascending variation. B) Upper lid, traced with an independent
line (Li1) with an approximate length of 2 cm, depicts an average temperature of 23.9 °C, which is higher than the two previous ones (0.5 °C
and 0.4 °C, respectively). The lower lid, traced with an independent line (Li2) of 2 cm, depicts a lower average temperature of 23.2 °C (0.3 °C
below the periocular); despite having been nursed on colostrum, and where a more significant heat loss is evidenced. Maximal temperature
is indicated with a red triangle and the minimal with a blue triangle.
Likewise, monitoring the minimal body temperature
with the use of IRT could provide valuable information in a
non-invasive way through the different thermal windows to
be able, in the future, to determine the ideal regions for
newborn monitoring. Figure 7 depicts IRT data derived from
preliminary studies in puppies performed by the present
authors, showing a newborn puppy from a eutocic whelping.
On the other hand, the clutch's handling must be
adequate because the newborn puppy’s immaturity of the
newborn puppy makes it vulnerable to a high mortality rate
on the first days. Evaluation of their performance at birth
allows identifying those newborns that require additional
support to that provided by the mother, which could increase
this species’ survival of this species.
5. Thermographic findings in the hypothermia model of
the newborn
The incidence of hypothermia in veterinary medicine
patients is still unknown; however, it is known that despite
advances many unknowns have still to be resolved to be able
to introduce techniques for its treatment. In the last years,
therapeutic hypothermia has been appropriately introduced
for disease processes in humans and veterinary medicine
(Brodeur et al 2017), focusing on reducing the metabolic
demand (Polderman 2009; Sinclair and Andrews 2010). The
therapy involves three stages for its application: induction,
maintenance, and rewarming (Polderman and Herold 2009);
however, despite the efforts, each stage is associated with
certain complications, like, for example, hypoalbuminemia
when inducing low temperatures as well as electrolytic
alterations. On the other hand, in veterinary medicine, its use
in small breeds has been successful with a 90% survival in
surgical processes, where induction of low temperatures is
low and for less time, as reported by Moon and Ilkiw (1993).
For these reasons, monitoring with IRT the first
minutes of life could help modify the care protocols of
temperature and instrument integrated monitoring of
diverse physiological processes (Abbas and Leonhardt 2014;
Buddharaju et al 2007). It is to be remembered that when
talking of evaluating the animal’s welfare in veterinary
medicine, this implies not just a continuous follow-up of its
vital parameters but also monitoring of its emotional state
and locomotion capacity (Vainer 2018), mechanisms that can
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be observed and assessed through a non-invasive method as
is IRT.
There is still a long way to clarify the mechanisms that
could help reduce neurological alterations, more studies are
needed to understand the disease processes, hence, it is
important to innovate and incorporate adequate techniques.
Figure 7 Minimal temperature expressed by the newborn puppy: wet, dry, post-colostrum, and 60 min post-colostrum. Note the temperature
of the puppy wet with amniotic fluid in the abdominal and thoracic regions with 21.9ºC. When the puppy is dry, the temperature increases by
0.34°C in the thorax and 0.152°C in the abdominal region; diminishing 0.39°C in the thorax regions and 0.05°C in the abdominal region in the
post-colostrum stage. Finally, 60-min post-colostrum, there are considerable increments of 2.11°C in the thoracic region and 1.05°C in the
abdominal region. Regarding the anterior and posterior extremities, these present a temperature of 22.6°C and 21.35°C, respectively, which
diminishes 0.3°C in the anterior extremity and 0.89°C in the posterior. However, there is an increase of 0.23°C for anterior extremities and of
0.35°C for the posterior. Finally, both regions evidence an increase in temperature of 0.77°C and 0.93°C, respectively, at 60 min post-colostrum.
The periocular region shows 23.75°C in the wet puppy; afterward, the temperature varies slightly, with 23.6°C in the dry puppy, 23.55°C in the
post-colostrum, and 23.57°C in the 60-min post-colostrum.
5. Final Considerations
Thermoregulation in an altricial species, as the
newborn puppy, differs from that of other species of which
registries are available. Their morphological variability
implies that the characteristics exhibited at birth are different
even within the same species, making it difficult to establish
the same handling and care protocols. The information
available up to now on their low thermoregulating capacity
due to the low percentage of brown fat tissue should become
a guideline to establish additional handling of the
environmental conditions surrounding the newborn, leading
to achieving an increase in the survival indices.
In turn, the mechanisms known to generate a heat
gain, like the shivering reflex and the vasoconstriction
mechanisms, are not observed in this species or are not fully
developed until day 18 of life. Hence, the losses due to
hypothermia can be high if not detected in time.
Additionally, it must be pointed out that not only the
previously mentioned factors influence thermoregulation,
since the breed, but birth weight, environmental conditions,
and colostrum intake could also be involved in the loss of
newborn puppies during the first week of life due to
hypothermia.
Specifically, the heat lost due to evaporation is
translated into higher mortality in the post-partum stage
because the puppy at the time of birth is wet; rapidly, the
effect of air currents, prevailing in the facilities, and without
an immediate drying of the newborn, will accelerate the
cooling of the newborn. This can cause a temperature
descent that will trigger a severe hypothermia if not cared for
in time.
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All these factors as a whole could modify the vitality at
birth, including alterations due to hypothermia, like low
cardiac frequency, deficient inspiratory effort, and low
motility translated into an inferior displacement of the puppy
to find food.
Based on the above mentioned, a reduced feeding and
a low birth weight demerit the capacity of the puppy to
survive because its glycogen reserves are insufficient. Hence
the colostrum is the primary source of energetic supply in the
first 24 h post-birth, ensuring the food and warranting the
capacity to produce heat in less time and adequate nursing.
Infrared thermography is a non-invasive method used
in diverse species to evaluate and monitor the temperature
in diverse processes, for which the use of thermal windows
has been established. However, for newborn puppies,
information is extrapolated from other species to find a
better option according to the needs. Hence, more research
in this species during the first hours of life is needed, which
are the useful thermal windows to establish the monitoring
bases for particular processes, like hypothermia and its
collateral effects, leading to diminishing the mortality indices
to this complication.
Finally, it is important to point out that the dog serves
as a model to study altricial species and is of vital relevance
to establishing whether therapeutical hypothermia is useful
in veterinary medicine as a protocol to handle and care for
the alterations at birth that cause sequelae in the adult stage,
like perinatal asphyxia.
Conflict of Interest
The authors declare that they have no conflict of interest.
Funding
This research did not receive any financial support.
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