Microbial populations vary between the upper and lower respiratory tract, but not within biogeographic regions of the lung of healthy horses.

Understanding normal microbial populations within areas of the respiratory tract is essential, as variable regional conditions create different niches for microbial flora, and proliferation of commensal microbes likely contributes to clinical respiratory disease. The objective was to describe microbial population variability between respiratory tract locations in healthy horses. Samples were collected from four healthy adult horses by nasopharyngeal lavage (NPL), transtracheal aspirate (TTA), and bronchoalveolar lavage (BAL) of six distinct regions within the lung. Full-length 16S ribosomal DNA sequencing and microbial profiling analysis was performed. There was a large amount of diversity, with over 1797 ASVs identified, reduced to 94 taxa after tip agglomeration and prevalence filtering. Number of taxa and diversity were highly variable across horses, sample types, and BAL locations. Firmicutes, proteobacteria, and actinobacteria were the predominant phyla. There was a significant difference in richness (Chao1, p = 0.02) and phylogenetic diversity (FaithPD, p = 0.01) between NPL, TTA, and BAL. Sample type (p = 0.03) and horse (p = 0.005) contributed significantly to Bray-Curtis compositional diversity, while Weighted Unifrac metric was only affected by simplified sample type (NPL and TTA vs BAL, p = 0.04). There was no significant effect of BAL locations within the lung with alpha or beta diversity statistical tests. Overall findings support diverse microbial populations that were variable between upper and lower respiratory tract locations, but with no apparent difference in microbial populations of the six biogeographic regions of the lung, suggesting that BAL fluid obtained blindly by standard clinical techniques may be sufficient for future studies in healthy horses.

Hyponatremia in horses with septic pneumopathy.

BACKGROUND: Hyponatremia is common in horses with bacterial pleuropneumonia, but no further characterization of this abnormality has been reported. OBJECTIVES: Describe admission plasma sodium concentration ([Na]) in horses with septic pneumopathy and evaluate any association of plasma [Na] with markers of systemic inflammation. ANIMALS: Medical records of horses >1 month of age that between 2008 and 2021 had a transtracheal aspirate (TTA) performed, abnormal TTA cytology, positive TTA culture, pulmonary disease on ultrasonography, radiography or both, and plasma [Na] assessed by direct ion-selective-electrode (dISE). Horses with concurrent diarrhea or azotemia were excluded. METHODS: Clinical and clinicopathological variables of interest between hypo- and normonatremic horses were compared. Spearman correlation and Fisher exact tests were used to identify significant associations (P < .05). RESULTS: Twenty of 35 horses had hyponatremia (median, 132 mmol/L; 25-75th interquartile range [IQR], 129.7-133.1 mmol/L; reference range, 134.2-138.4 mmol/L). A higher proportion of horses with systemic inflammatory response syndrome (SIRS) had hyponatremia (P = .01). Hyponatremic patients had higher mean plasma fibrinogen concentration (461 ± 160.5 mg/dL; P = .01) and higher rectal temperature (38.8 ± 0.7°C; P = .02) than normonatremic horses. Negative correlations were found between plasma [Na] and fibrinogen (P = .001; ρ = -0.57) concentrations and between plasma [Na] and rectal temperature (P = .001; ρ = -0.51). Presence or absence of pleural effusion did not influence severity of hyponatremia. Mean duration of hospitalization was longer (P = .04) in hyponatremic horses (9.8 ± 6.6 days). CONCLUSIONS AND CLINICAL IMPORTANCE: Hyponatremia at admission is associated with the presence of inflammation, SIRS, and with longer duration of hospitalization.

Plasma ascorbic acid, antioxidant capacity, and reactive oxygen species in healthy foals.

OBJECTIVE: To describe ascorbic acid (AA) concentrations, plasma antioxidant capacity (PAC) and markers of oxidative stress, as measured by derivatives of reactive oxygen metabolites (dROMs), in healthy foals at birth and during the first month of life. SAMPLES: Venous blood samples were collected from healthy Standardbred (n = 13) and Quarter Horse (n = 10) foals. Plasma AA, PAC, and dROMs were assessed at 3 to 12 hours, 3 days, and 1, 2, and 4 weeks of age. PROCEDURES: AA was measured via high-performance liquid chromatography. PAC and dROMs were measured with a free radical analytical system. Comparisons of AA, PAC, and dROMs at different time points were assessed. RESULTS: Mean ± standard deviation AA concentrations at 3 to 12 hours (44.7 ± 19.6 µmol/L; P ≤ .01), 1 (48.6 ± 22.5 µmol/L; P ≤ .001), and 2 weeks (41.8 ± 15.8 µmol/L; P ≤ .001) were higher than at 4 weeks of age (28.5 ± 12.7 µmol/L). Both PAC and dROMs significantly increased at different time points compared to 3 to 12 hours of age. CLINICAL RELEVANCE: Healthy foals have higher plasma AA concentrations shortly after birth, which then gradually decrease throughout the first month of life, suggesting that AA may represent a key antioxidant in the postnatal period. The concurrent increase in PAC and dROMs suggests that dynamic development of oxidative balance occurs after birth in foals. Development of AA, PAC, and dROM reference ranges in healthy foals could be used to guide therapeutic interventions and monitor during disease states characterized by increased oxidative stress.

Normal regression of the internal umbilical remnant structures in Standardbred foals.

BACKGROUND: Diseases affecting the internal umbilical remnant are common in foals. Ultrasound is used to diagnose abnormalities of these structures, and to monitor treatment. However, little is known about the progression of normal internal umbilical remnant regression. OBJECTIVES: To document normal regression of the umbilical remnant in foals over the first 6 weeks of life. STUDY DESIGN: Prospective, longitudinal cohort study. METHODS: Weekly ultrasound examinations were performed beginning at 1 day of age in 34 healthy Standardbred foals. The umbilical vein was measured in cross section just cranial to the external umbilicus, at the level of the liver and midway between these points. The umbilical arteries were measured in cross section just caudal to the external umbilicus, at the apex of the bladder and at the midpoint of the bladder. The urachus was imaged longitudinally as it exited the bladder. Reduction in size over time was evaluated as percentage change in diameter. RESULTS: Structure diameter decreased linearly over time. The largest measurements were at 24 hours of age with a median umbilical vein diameter of 0.83 cm (IQR 0.77-1.02 cm), median umbilical artery diameter of 0.61 cm (IQR 0.56-0.70 cm) and median urachal diameter of 1.07 cm (IQR 1.02-1.14 cm). There was a significant reduction in diameter for all structures (16.0%-21.9%; corrected P < .001) within the first week of life. MAIN LIMITATIONS: All foals were of a single breed, and examinations and measurements were performed by multiple individuals. CONCLUSIONS: The internal umbilical remnants (umbilical vein/arteries, and urachus) rapidly regress over the first few weeks of life. The median internal umbilical remnant diameters reported here are smaller than previously reported values, emphasising the importance of accounting for age when diagnosing umbilical abnormalities. In a healthy Standardbred foal, normal structures are difficult to definitively identify via transcutaneous ultrasound by 5-6 weeks of age.