Vitality in Newborn Farm Animals: Adverse Factors, Physiological Responses, Pharmacological Therapies, and Physical Methods to Increase Neonate Vigor

Abstract

Vitality is the vigor newborn animals exhibit during the first hours of life. It can be assessed by a numerical score, in which variables, such as heart rate, respiratory rate, mucous membranes' coloration, time the offspring took to stand up, and meconium staining, are monitored. Vitality can be affected by several factors, and therapies are used to increase it. This manuscript aims to review and analyze pharmacological and physical therapies used to increase vitality in newborn farm animals, as well as to understand the factors affecting this vitality, such as hypoxia, depletion of glycogen, birth weight, dystocia, neurodevelopment, hypothermia, and finally, the physiological mechanism to achieve thermostability. It has been concluded that assessing vitality immediately after birth is essential to determine the newborn's health and identify those that need medical intervention to minimize the deleterious effect of intrapartum asphyxia. Vitality assessment should be conducted by trained personnel and adequate equipment. Evaluating vitality could reduce long-term neonatal morbidity and mortality in domestic animals, even if it is sometimes difficult with the current organization of some farms. This review highlights the importance of increasing the number of stock people during the expected days of parturitions to reduce long-term neonatal morbidity and mortality, and thus, improve the farm's performance.

Keywords: BAT; MAS; domestic animals; meconium staining; shivering; vitality.

Figure 1

Hypoxia is a factor that reduces vitality. During intrapartum uterine contractions, uteroplacental blood vessels and the umbilical cord are compressed. Due to this compression, partial fetal pressure of arterial oxygen (PaO₂) is reduced, causing transient hypoxemia in the fetus. When uterine contractions increase or uterine hyperstimulation occurs, around 60% of the uteroplacental blood circulation is reduced, affecting transplacental gas exchange and fetal oxygen supplementation. Along with hypoxemia, other physiological events, such as acidosis, hypercarbia, and meconium aspiration, can also be present, reducing a newborn’s vitality.

Figure 2

Importance of birth weight in the percentage of newborn survival. (A) In newborns with low birth weight, there are many limitations to being able to produce energy from their glycogen reserves in the liver and skeletal muscle because these are reduced between 75 and 80%. Cori’s cycle cannot be activated correctly because muscle fibers are reduced per µm², and the lamb cannot get up and look for the mother’s teat, so it may starve to death. Low birth weight is closely associated with fetal and neonatal morbidity, inhibited growth and cognitive development, and chronic diseases. During oxygen deprivation in the event of fetal hypoxia–ischemia, compensatory mechanisms are responsible for redistributing cardiac output, centralizing blood flow to vital organs, and reducing oxygen consumption. Additionally, an increase in peristalsis with expulsion and staining of meconium on the skin can be present, as illustrated in the lamb on the left side. (B) In contrast, high-birth-weight newborns have adequate vigor, can stand up immediately to consume colostrum, and have enough energy reserves. These reserves help to achieve thermoneutrality, together with the higher amount of muscle fibers, and enough hepatic glycogen reserves. In addition, the lipid reserves in lambs born with normal weights is 10× the amount of available lipids in those that have low birth weight. Although normal-weight newborns have increased chances to survive, when the female has a narrow birth canal, these animals can experience dystocia and a prolonged expulsion period that might predispose them to meconium aspiration. Type IIA: muscular fibers type IIA.

Figure 3

Amount and distribution of brown adipose tissue (BAT) in lambs, calves, and kid goats. According to the species, different levels of BAT are available at birth. For example, concerning the animal’s weight at birth, newborn lambs have less pericardial BAT (4.61 g) than calves after birth (23 g). Similarly, perirenal adipose tissue is higher in calves (146 g vs. 28.5 g) and the only reported source in kids, which have 3.2 g of BAT. These values influence the ability of newborns to thermoregulate and prevent critical heat losses. NE: norepinephrine; TG: triglycerides; UCP1: uncoupling protein 1.

Figure 4

Cardiorespiratory and neural effects of caffeine. The mechanism of action of caffeine, binding to adenosine receptors (A1, A2A, A2B, and A3) in the cell membrane, causes cardiac responses that can improve a newborn’s vitality by increasing heart rate, cardiac contractility, and blood pressure. Moreover, it acts on postsynaptic neurons and in the blockade of A1 and A2A. Binding these receptors increases arousal and alertness by accumulating adrenaline and activating the dopaminergic system. ATP: adenosine triphosphate; cAMP: cyclic adenosine monophosphate.

Figure 5

Thermal response of newborn piglets, evaluated by infrared thermography. Through infrared thermography and the delimitation of the region of interest in the pelvic limb (El1), factors such as weight and birth order can be assessed and associated with low birth temperatures, as shown in piglets from the same litter. (A) A piglet with a low birth weight (0.60 kg) and birth order eight had a minimum temperature of 23.4 °C. (B) A newborn weighing 0.62 kg and birth order five had a minimum temperature of 26.5 °C. In contrast, when comparing piglets from birth order one (C) and three (D) (weighing 1.58 and 1.63 kg, respectively), the minimum temperature of piglet (C) (32.1 °C) is 8.7 °C above piglet (A) and 5.6 °C above piglet (B). Minimum temperature of piglet (D) (27 °C) is maintained higher than (A,B). Red triangles mark the maximum temperature and blue triangles the minimum values in each thermal window.

Figure 6

Comparison between central and peripheral thermal windows in newborn calves of water buffaloes with different thermal states. (A) Normothermic newborn. Central thermal windows, such as periocular (El1) and auricular (El2), have an average temperature of 37.3 °C and 37.0 °C, respectively. Peripheral regions considered in the elbow (El3) and metacarpal region (El4) show average values of 29.2 °C and 30.0 °C. (B) Hypothermic newborn. In contrast to buffalo neonates with thermostability, this animal shows lower temperatures in both central and peripheral temperature. The temperature was lower in the periocular window (El1) by 1 °C and in the auricular region (El2) by 0.9 °C. In peripheral windows at the elbow (El3) and metacarpal region (El4), the temperature dropped by 0.7 °C and 2 °C, respectively. The significantly marked difference between the central and peripheral windows shows that an animal with hypothermia at birth generates microcirculatory changes to preserve body heat in the brain. This leads to the activation of the Autonomic Nervous System, its sympathetic branch, and the neurosecretion of catecholamines that cause peripheral vasoconstriction to prevent further heat loss. This would explain the response observed in the radiometric images of newborn buffaloes with hypothermia. Red triangles mark the maximum temperature and blue triangles the minimum values in each thermal window.