Thyroid hormone concentrations in foals affected by perinatal asphyxia syndrome

Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals

Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.

Study on NGF and VEGF during the Equine Perinatal Period-Part 2: Foals Affected by Neonatal Encephalopathy

Neonatal Encephalopathy (NE) may be caused by hypoxic ischemic insults or inflammatory insults and modified by innate protective or excitatory mechanisms. Understanding the underlying pathophysiology is important in formulating a rational approach to diagnosis. The preliminary aim was to clinically characterize a population of foals spontaneously affected by NE. The study aimed to: (i) evaluate nerve growth factor (NGF) and vascular endothelial growth factor (VEGF) levels in plasma samples obtained in the affected population at parturition from the mare’s jugular vein, umbilical cord vein and foal’s jugular vein, as well as in amniotic fluid; (ii) evaluate the NGF and VEGF content in the plasma of foals affected by NE during the first 72 h of life/hospitalization; (iii) evaluate NGF and VEGF levels at birth/admission in relation to selected mare’s and foal’s clinical parameters; (iv) evaluate the relationship between the two trophic factors and thyroid hormone levels (TT3 and TT4) in the first 72 h of life/hospitalization; and (v) assess the mRNA expression of NGF, VEGF and brain-derived neurotrophic factor (BDNF), and their cell surface receptors, in the placenta of mares that delivered foals affected by NE. Thirteen affected foals born from mares hospitalized for peripartum monitoring (group NE) and twenty affected foals hospitalized after birth (group exNE) were included in the study. Dosage of NGF and VEGF levels was performed using commercial ELISA kits, whereas NGF, VEGF, and BDNF placental gene expression was performed using a semi-quantitative real-time PCR. In group NE, NGF levels decreased significantly from T0 to T24 (p = 0.0447) and VEGF levels decreased significantly from T0 to T72 (p = 0.0234), whereas in group exNE, only NGF levels decreased significantly from T0 to T24 (p = 0.0304). Compared to healthy foals, a significant reduction of TT3 levels was observed in both NE (T24, p = 0.0066; T72 p = 0.0003) and exNE (T0, p = 0.0082; T24, p < 0.0001; T72, p < 0.0001) groups, whereas a significant reduction of TT4 levels was observed only in exNE group (T0, p = 0.0003; T24, p = 0.0010; T72, p = 0.0110). In group NE, NGF levels were positively correlated with both TT3 (p = 0.0475; r = 0.3424) and TT4 levels (p = 0.0063; r = 0.4589). In the placenta, a reduced expression of NGF in the allantois (p = 0.0033) and a reduced expression of BDNF in the amnion (p = 0.0498) were observed. The less pronounced decrease of the two trophic factors compared to healthy foals, their relationship with thyroid hormones over time, and the reduced expression of NGF and BDNF in placental tissues of mares that delivered affected foals, could be key regulators in the mechanisms of equine NE.

Study on NGF and VEGF during the Equine Perinatal Period-Part 1: Healthy Foals Born from Normal Pregnancy and Parturition

The importance of trophic factors, such as nerve growth factor (NGF), vascular endothelial growth factor (VEGF), and brain-derived neurotrophic factor (BDNF) during the perinatal period, is now emerging. Through their functional activities of neurogenesis and angiogenesis, they play a key role in the final maturation of the nervous and vascular systems. The present study aims to: (i) evaluate the NGF and VEGF levels obtained at parturition from the mare, foal and umbilical cord vein plasma, as well as in amniotic fluid; (ii) evaluate NGF and VEGF content in the plasma of healthy foals during the first 72 h of life (T0, T24 and T72); (iii) evaluate NGF and VEGF levels at parturition in relation to the selected mares’ and foals’ clinical parameters; (iv) evaluate the relationship between the two trophic factors and the thyroid hormone levels (TT3 and TT4) in the first 72 h of life; (v) assess mRNA expression of NGF, VEGF and BDNF and their cell surface receptors in the placenta. Fourteen Standardbred healthy foals born from mares with normal pregnancies and parturitions were included in the study. The dosage of NGF and VEGF levels was performed using commercial ELISA kits, whereas NGF, VEGF and BDNF placental gene expression was performed using semi-quantitative real-time PCR. In foal plasma, both NGF and VEGF levels decreased significantly over time, from T0 to T24 (p = 0.0066 for NGF; p < 0.0001 for VEGF) and from T0 to T72 (p = 0.0179 for NGF; p = 0.0016 for VEGF). In foal serum, TT3 levels increased significantly over time from T0 to T24 (p = 0.0058) and from T0 to T72 (p = 0.0013), whereas TT4 levels decreased significantly over time from T0 to T24 (p = 0.0201) and from T0 to T72 (p < 0.0001). A positive correlation was found in the levels of NGF and VEGF in foal plasma at each time point (p = 0.0115; r = 0.2862). A positive correlation was found between NGF levels in the foal plasma at T0 and lactate (p = 0.0359; r = 0.5634) as well as between VEGF levels in the foal plasma at T0 and creatine kinase (p = 0.0459; r = 0.5407). VEGF was expressed in all fetal membranes, whereas NGF and its receptors were not expressed in the amnion. The close relationship between the two trophic factors in foal plasma over time and their fine expression in placental tissues appear to be key regulators of fetal development and adaptation to extra-uterine life.

Treatments and therapeutic protocols for the recovery of an asphyxiated new-born: A review of pre-clinical and clinical studies in human neonates and in different animal models

The objective of this review is to ascertain the advantages and disadvantages of several treatments and therapeutic protocols that have been used for the prevention and treatment of perinatal asphyxia in human neonates and in different animal models. Perinatal asphyxia is one of the main causes of mortality worldwide and is an important factor in triggering physio-metabolic disorders that result in serious neurological consequences and learning disorders not only in human foetuses and neonates, but also in animals. In recent years, the search for new pharmacological protocols to prevent and reverse physio-metabolic disorders and brain damage derived from perinatal asphyxia has been and continues to be the subject of intense research. Currently, within these pharmacological protocols, therapeutic strategies have been evaluated that use respiratory and hormonal stimulants, as well as hypothermic therapies in combination with other putative neuroprotective agents. Similarly, energy supplements have been evaluated with the objective of preventing perinatal asphyxia and treating new-borns with this condition, and to decrease the incidence of neonatal and foetal deaths associated with it. However, despite these promising advances, this pathology has persisted, since the administration of these therapies in low doses may not exert a neuroprotective effect or, in high doses, can trigger adverse effects (such as reduced cardiac contractility, reduced cerebral blood flow, poor perfusion, sympathetic and neuroendocrine stimulation, and increased blood viscosity) in human foetuses and neonates as well as in different animal models (rats, piglets, sheep and rabbits). Therefore, it is important to determine the minimum effective dose with which these therapies exert a neuroprotective effect, as well as the mode of administration, the duration of therapy, etc. Therefore, until a powerful strategy is found to improve the consequences of suffocation, this topic will continue to be the subject of intensive research in the future.

Hair Cortisol and DHEA-S in Foals and Mares as a Retrospective Picture of Feto-Maternal Relationship under Physiological and Pathological Conditions

Equine fetal hair starts to grow at around 270 days of pregnancy, and hair collected at birth reflects hormones of the last third of pregnancy. The study aimed to evaluate cortisol (CORT) and dehydroepiandrosterone-sulfate (DHEA-S) concentrations and their ratio in the trichological matrix of foals and mares in relation to their clinical parameters; the clinical condition of the neonate (study 1); the housing place at parturition (study 2). In study 1, 107 mare-foal pairs were divided into healthy (group H; n = 56) and sick (group S; n = 51) foals, whereas in study 2, group H was divided into hospital (n = 30) and breeding farm (n = 26) parturition. Steroids from hair were measured using a solid-phase microtiter radioimmunoassay. In study 1, hair CORT concentrations measured in foals did not differ between groups and did not appear to be influenced by clinical parameters. A correlation between foal and mare hair CORT concentrations (p = 0.019; r = 0.312, group H; p = 0.006; r = 0.349, group S) and between CORT and DHEA-S concentrations in foals (p = 0.018; r = 0.282, group H; p < 0.001; r = 0.44, group S) and mares (p = 0.006; r = 0.361, group H; p = 0.027; r = 0.271, group S) exists in both groups. Increased hair DHEA-S concentrations (p = 0.033) and decreased CORT/DHEA-S ratio (p < 0.001) appear to be potential biomarkers of chronic stress in the final third of pregnancy, as well as a potential sign of resilience and allostatic load in sick foals, and deserve further attention in the evaluation of prenatal hypothalamus-pituitary-adrenal (HPA) axis activity in the equine species. In study 2, hormone concentrations in the hair of mares hospitalized for attended parturition did not differ from those that were foaled at the breeding farm. This result could be related to a too brief period of hospitalization to cause significant changes in steroid deposition in the mare’s hair.

Prediction for late-onset sepsis in preterm infants based on data from East China

AIM

To construct a prediction model based on the data of premature infants and to apply the data in our study as external validation to the prediction model proposed by Yuejun Huang et al. to evaluate the predictive ability of both models.

METHODS

In total, 397 premature infants were randomly divided into the training set (n = 278) and the testing set (n = 119). Univariate and multivariate logistic analyses were applied to identify potential predictors, and the prediction model was constructed based on the predictors. The area under the curve (AUC) value, the receiver operator characteristic (ROC) curves, and the calibration curves were used to evaluate the predictive performances of prediction models. The data in our study were used in the prediction model proposed by Yuejun Huang et al. as external validation.

RESULTS

In the current study, endotracheal intubation [odds ratio (OR) = 10.553, 95% confidence interval (CI): 4.959-22.458], mechanical ventilation (OR = 10.243, 95% CI: 4.811-21.806), asphyxia (OR = 2.614, 95% CI: 1.536-4.447), and antibiotics use (OR = 3.362, 95% CI: 1.454-7.775) were risk factors for late-onset sepsis in preterm infants. The higher birth weight of infants (OR = 0.312, 95% CI: 0.165-0.588) and gestational age were protective factors for late-onset sepsis in preterm infants. The training set was applied for the construction of the models, and the testing set was used to test the diagnostic efficiency of the model. The AUC values of the prediction model were 0.760 in the training set and 0.796 in the testing set.

CONCLUSION

The prediction model showed a good predictive ability for late-onset sepsis in preterm infants.

Serum cortisol and thyroid hormone concentrations and survival in foals born from mares with experimentally induced ascending placentitis

Background

There are few publications on occurrence of nonthyroidal illness syndrome in foals and on the prognostic value of cortisol and thyroid hormone (TH) concentrations in newborn foals.

Objectives

To determine serum cortisol and TH concentrations (total and free thyroxine: T₄ and _FT₄; total and free triiodothyronine: T₃ and _FT₃) in foals born from mares with placentitis, to determine their association with survival, and their use as prognostic markers.

Animals

A cohort of 29 newborn foals comprising 5 Control, 14 Low‐risk, and 10 Sick foals were evaluated over the first week of life.

Methods

In this prospective study foals born to mares with experimentally‐induced placentitis were assigned to Low‐risk or Sick groups while foals born to control mares were classified as Control based on clinical findings. Foals were also classified as Term (n = 13), Dysmature (n = 7), or Premature (n = 9), and survival rate was recorded. Serum cortisol and TH hormone concentrations were measured at 0, 12, 24, 48, and 168 hours of life.

Results

Sick non‐surviving foals had lower (P < .05) T₃ : cortisol ratio at 12 (3.68 ± 1.06 versus 18.58 ± 2.78), 24 (5.47 ± 2.34 versus 23.40 ± 3.82), and 48 (10.47 ± 6.29 versus 26.6 ± 2.90) hours of life when compared to Sick surviving foals and lower (P < .05) T₄ : cortisol ratio at 12 (75.12 ± 21.71 versus 414.47 ± 58.47) and 24 hours (127.83 ± 55.21 versus 430.87 ± 80.31) after birth than Sick surviving foals.

Conclusion and Clinical Importance

Placental infections can impair fetal thyroid function. Low T₃ : cortisol and T₄ : cortisol ratios seem to be good prognostic markers in newborn foals.

Clinical Pathology in the Foal

The dynamic physiologic changes and unique diet during the neonatal period contribute to key differences in clinicopathologic test results of healthy foals relative to healthy adult horses. When reporting results, most diagnostic laboratories only provide reference intervals for mature horses. Thus, failure to recognize the unique differences that occur in foals relative to adult horses can lead to erroneous interpretation of neonatal clinical pathologic values. Thus, the main objective of this article was to review distinct features of common clinicopathologic tests in foals, relative to mature horses.

Equine Neonatal Encephalopathy: Facts, Evidence, and Opinions

Neonatal encephalopathy (NE) and neonatal maladjustment syndrome (NMS) are terms used for newborn foals that develop noninfectious neurologic signs in the immediate postpartum period. Cerebral ischemia, hypoxia, and inflammation leading to neuronal and glial dysfunction and excitotoxicity are considered key mechanisms behind NE/NMS. Attention has been placed on endocrine and paracrine factors that alter brain cell function. Abnormal steroid concentrations (progestogens, neurosteroids) have been measured in critically ill and NE foals. In addition to supportive treatment, antimicrobials should be considered. Controversies regarding the pathophysiology, diagnosis, and treatment of NE and NMS will remain until controlled mechanistic and therapeutic studies are conducted.

Determination of reference intervals for umbilical cord arterial and venous blood gas analysis of healthy Thoroughbred foals

Although umbilical cord blood gas analysis is considered the best way to assess in utero oxygenation in human neonates, there is limited evaluation of this method in equine neonatology. Our objectives were to assess the practicality of obtaining umbilical cord blood gas samples in the field and to determine umbilical cord arterial and venous blood gas reference intervals (RI) for healthy, newborn foals. Thoroughbred foals >320 days gestation from healthy mares with uneventful pregnancies at one stud farm were evaluated. All parturitions were observed, with paired umbilical arterial and venous whole-blood samples obtained immediately following parturition for blood gas and lactate concentrations measured in duplicate. Apgar scores were assigned immediately and 10 min after birth, with all foals subsequently examined on days 1-28 to monitor for development of perinatal asphyxia syndrome. Foals were excluded from analysis based on abnormalities of stage 2 labour, Apgar scores and gross and histological placental assessment. Data was analysed using a Student's t-test, Pearson's correlation and the Robust method with P ≤ 0.05 significant. Umbilical cord samples were simple to obtain with minimal disruption to the foaling environment. Of the n = 34 foals assessed, n = 7 were excluded based on premature placental separation deliveries. The mean time for stage 2 labour and blood gas analysis after parturition was 17.3 ± 5.1 min and 5.0 ± 2.3 min, respectively. RI were identified for umbilical arterial and venous pH (7.19-7.42 vs. 7.34-7.44), PO₂ (15.5-48.39 mmHg vs. 16.6-52.7 mmHg), PCO₂ (49.5-82.29 mmHg vs. 45.4-63.1 mmHg), SO₂ (9.19-76.89% vs. 39.9-84.88%), bicarbonate (27.3-38.7 mmol/l vs. 27.7-37.8 mmol/l), base excess (0.36-12.9 mmol/l vs. 1.97-13.1 mmol/l), TCO₂ (28.99-40.3 mmHg vs. 29.0-39.5 mmHg) and lactate (1.4-7.3 mmol/l vs. 1.3-4.9 mmol/l). Umbilical arterial samples had lower pH (P < 0.0001), PO₂ (P = 0.002) and SO₂ (P < 0.0001) and higher PCO₂ (P < 0.0001) and lactate (P < 0.0001) than venous samples. The initial Apgar score was positively correlated to umbilical arterial SO₂ (r = 0.4, P = 0.05) and negatively with umbilical arterial TCO₂ (r = -0.6, P = 0.004). Overall, umbilical cord sampling was simple and minimally disruptive, with RI obtained for blood gas measurements. RI for umbilical blood gas measurements from a larger population of healthy and unhealthy foals is required to evaluate the accuracy of this method for assessing in utero oxygenation.

Serum Thyroid Hormone and Thyrotropin Concentrations in Adult Horses as They Age

With more horses remaining active longer in life, it is important to characterize changes that occur normally with aging, so that these can be differentiated from development of disease. The objective of the study was to test the hypotheses that geriatric horses have lower circulating concentrations of thyroid hormones and/or higher serum thyrotropin (TSH) concentrations compared to younger horses. Serum thyroid hormone and TSH concentrations from 71 normal, healthy horses that had participated in prior research projects were analyzed for effects of age, sex, and season when samples were obtained. All samples had been assayed in the same previously validated radioimmunoassays. There were no differences in serum concentrations of thyroid hormones or TSH by sex or season. Serum total thyroxine (T4) was greater in 3- to 6-year-old horses compared to all other age groups and was negatively correlated with age. There were no differences among age groups for free T4 and total and free tri-iodothyronine (T3). Serum TSH concentration was significantly greater in old horses (≥15 or ≥20 years) compared to young (3-10 years) and intermediate (11-14 years) age groups. Serum TSH was positively correlated with age. There were no significant differences in thyroid hormone responses to thyrotropin releasing hormone (TRH) among young, intermediate, or old horses. However, the TSH response to TRH was significantly different in both groups of older horses compared to intermediate and young horses. Serum total thyroxine concentrations decrease and serum TSH concentrations increase in horses as they age, with no changes in free T4 or T3.

[Congenital goiter in the neonatal foal. Two case reports. Zwei Fallberichte]

Two cases of an innate hyperplastic goiter in foals as well as the sonographic evaluation of the hyperplastic gland are presented. One foal displayed skeletal deformities in the form of a mandibular prognathism and forelimb contractures in addition to the swollen thyroid gland. Because of a poor prognosis, the animal was euthanized. The second foal was premature and displayed respiratory signs. Under symptomatic therapy, the goiter regressed within a few weeks.

Thyroid function and dysfunction in term and premature equine neonates

Background

This study was performed to compare thyroid function of premature foals to term foals.

Hypothesis

Premature foals are more markedly hypothyroxinemic than expected for their severity of illness alone.

Animals

Twenty clinically normal term foals; 28 sick, hospitalized term foals; 24 sick, hospitalized premature foals.

Methods

Thyroid hormones (TH) and thyrotropin (TSH) were measured, both at rest and in response to thyrotropin‐releasing hormone (TRH), in the 3 groups of foals. Clinical and clinicopathologic data were recorded.

Results

Normal foals had high TH at birth, which decreased over the first month into the normal reference range for adult horses. TSH was within the normal adult reference range soon after birth, and did not change over time. At 24–36 hours of age, triiodothyronine (T3) was significantly lower in both premature and term hospitalized foals compared to normal foals; premature foals were not different from term hospitalized foals. Thyroxine (T4) was not different between normal and term hospitalized foals, but was significantly lower than in premature foals of both of these groups. TSH was not different among the 3 groups. TRH stimulation tests identified significant differences in T4 among all 3 groups of foals, whereas T3 was similar in premature and term hospitalized foals and different from normal foals. TSH response to TRH was significantly higher in premature foals compared to normal foals.

Conclusions and Clinical Importance

The hypothalamic‐pituitary‐thyroid axis is different in foals compared to adult horses. Sick foals exhibit nonthyroidal illness syndrome. Premature foals are more markedly hypothyroxinemic than can be accounted for by their severity of illness alone.