Kids Are Not Just Small Goats

One of the primary anatomic differences between goats and human children is the presence of a complex forestomach system. At birth, the goat kid is born with an underdeveloped forestomach system, and as a result, their gastrointestinal system is more similar to that of a simple stomached animal such as the human (Fig 2).¹  During this period, the goat kid utilizes the rumenoreticular groove, which shunts milk from the esophagus to the abomasum, with the abomasum functioning to secrete digestive acid much like the human stomach.^2,3  Once fully matured (typically by approximately 12 weeks of age), the forestomach system begins with the esophagus, which terminates at the first and largest forestomach section known as the reticulorumen. Composed of a reticulum and rumen, which are only partially separated by a muscular wall, the reticulorumen functions primarily to ferment ingested biomass into amino acids, volatile fatty acids, and gases such as ammonia.^1,3  The reticulorumen then connects to the omasum, which functions to absorb water and nutrients, before ending in the final component of the stomach system, the abomasum, which again has a similar function to the stomach of a human.^1,4  In contrast, the human child only possesses a single stomach, and as a result, any food-containing pouch proximal to the stomach is considered abnormal and should be investigated for etiologies such as an esophageal diverticulum, esophageal atresia, or tracheoesophageal fistula.⁵ 

The overall fluid composition of human children and goats is similar, with approximately 60% of total body weight being composed of water in both.^6,7  Maintenance fluid requirements differ somewhat, with adult goats requiring between 2 and 3 mL of fluids per kg per hour, and human children requiring fluids according to the “4–2–1 rule,” in which the first 10 kg require 4 mL per kg, the second 10 kg requiring 2 mL per kg, and any subsequent kilograms requiring 1 mL per kg.^6–8  In choosing fluids, isotonicity is similar between goats and human children, with 0.9% normal saline and lactated Ringer’s solution both being acceptable crystalloids.^6,7 

The main difference to consider involves the water storage capacity of the goat rumen. Goats can store up to 4 to 5 days’ worth of fluid within the rumen, which allows them to both graze far from watering holes and survive in water-scant environments such as the desert.^3,9  Some, such as the black Bedouin goat, have been noted to drink up to 40% of their dry body weight in a span of just 3 to 10 minutes, and during such episodes of rapid rehydration, the rumen will temporarily store water so as to avoid osmotic shock and hemolysis.^3,10  Human children, on the other hand, have much more limited fluid reserves. Though no large clinical trials have yet evaluated the outcomes of human children left in the desert without access to water, the lack of a rumen in human children makes them more susceptible to insensible losses.

A significant difference in immunology between goats and human children occurs immediately after birth. Because of the structure of the goat’s synepitheliochorial placenta, no immunoglobulins are able to be transferred from mother to child in utero.^11,12  As a result, goats are born agammaglobulinemic and are entirely dependent on colostrum for passive immunity.¹²  Critically, this window for passive transfer only exists for approximately 24 hours after birth because only the original neonatal intestinal epithelial cells are able to absorb immunoglobulins via pinocytosis; these original cells are sloughed away by 24 hours of life, and the newborn goats are thus left unable to absorb any further immunoglobulins from colostrum or milk.¹²  Any failure of this passive transfer of immunity via colostrum significantly increases the risk of neonatal goat sepsis and subsequent death, which often presents within the first 48 hours of life.¹²  In contrast, the human neonate has a more robust immune system at birth. Because of transplacental transfer of immunoglobulins, primarily immunoglobulin G, human neonates are born with some level of passive immunity.¹³  This passive immunity is critical to the avoidance of neonatal sepsis, which, in what is perhaps an act of microbiologic collusion, is commonly caused by Escherichia coli and group B Streptococcus in both goat and human neonates.^12,14 

For both goats and humans, toxic ingestions can cause hemolytic anemia; however, 1 notable difference in potential triggers lies with the kale plant. Though human children may protest and insist that kale is poisonous to them, they can in fact tolerate consumption of this leafy green, unlike their goat counterparts who can experience hemolysis by way of oxidative stress. Specifically, Brassica species such as kale or Allium species such as garlic or onions contain S-methylcysteine sulphoxide, which, on its own, is relatively nontoxic despite its oxidant properties.¹⁵  However, reticulorumen bacteria metabolize S-methylcysteine sulphoxide into dimethyl disulphide, a potent oxidant that quickly depletes reduced glutathione stores before oxidizing hemoglobin directly and resulting in intravascular hemolysis with characteristic deposition of Heinz bodies within red blood cells.¹⁵  In cases of severe hemolysis, be it from toxins, infections, or trauma, packed red blood cell transfusions may be required. For goats, crossmatching is not routinely performed, particularly for first-time transfusions, because transfusion reactions are uncommon; however for humans, type- and crossmatching are recommended before red blood cell transfusions.¹²  Given this clinically significant difference in practice, which could result in adverse outcomes for patients if overlooked, hospitals may consider integrating a safety check into their transfusion protocols (Fig 3).

Traditionally within goat medicine, electrocardiograms (ECGs) have only been used to identify arrythmia or conduction abnormalities because of the limitations in goat electrical conduction pathways.¹⁶  Specifically in goats, Purkinje fibers penetrate from endocardium to epicardium, which results in rapid depolarization of both ventricles.¹⁷  This contrasts with human cardiac anatomy, in which Purkinje fibers primarily exist within the subendocardial space.¹⁸  Consequently for goats, changes in electrical axis and QRS morphology can be difficult to detect or absent altogether, with one study of goats with induced right ventricular hypertrophy showing no changes in the QRS complex.^17,19  Though oftentimes human child ECGs may seem similarly unhelpful given lack of compliance causing significant artifact and the dreaded “nonspecific T wave abnormalities,” there is in fact great clinical utility in ECGs to identify pathologies such as right heart strain, cardiomyopathies, or pericarditis.²⁰ 

The saying “kids are not just small adults” has recently taken on more meaning than ever, with many pediatric hospitalists being called upon to provide care for older patients given pandemic pressures.²¹  At our institution for example, pediatricians provided coverage on an adult ward and quickly learned the implications of differences between pediatric and adult physiology and evidence-based care recommendations. After reading this review, pediatric hospitalists should feel more prepared to tackle the possibility of expanding coverage to goats, as well, be it transfers from petting zoos or ambiguously worded question stems about Q fever. Though some of the epidemiology and physiology of goat kids and human kids overlap, clinicians must take care to not be complacent in their management, because there exist many differences that can dramatically alter the clinical course if not acted upon. Details such as crossmatching before transfusing human kids may elude those not specifically trained to do so, and subtle as they may be, recognition of these areas of divergence is key to delivering safe and excellent care to the kids entrusted to us. After all, when hearing the sound of hoofbeats, think of goats, not children.