A Clinical Analysis of the Effect of Antibiotic Administration on the Neonatal Foal Microbiome



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ABSTRACT A study was conducted to investigate the effects of antibiotic administration on the neonatal foal microbiome, complete blood count (CBC), and fibrinogen (FIB) concentration. Eleven stock-type newborn foals were studied in the clinical setting. Foals were enrolled in the trial within 24 h of birth and administered treatments according to CBC, fibrinogen, and veterinary decision. Foals were treated with an antibiotic (amikacin and ceftiofur, amikacin and penicillin, or trimethoprim/sulfadiazine; n = 7), or not treated (n = 4). Foals that did not respond to the initial antibiotic treatment based on CBC, fibrinogen, and veterinary supervision were administered subsequent treatment (n = 3). The trial began January 2018 and ended September 2018, with each foal being enrolled from birth to at least 56-d of age. Fecal samples were collected from foals at d 0, 7, 14, 21, 28, and 56. When a foal experienced approximately 1 mo without treatment or at 56 d, whichever was earliest, a corresponding dam fecal sample was collected by the consulting veterinarian or trained staff. Blood was obtained on d 0, 7, 14, 21, 28, and 56 and analyzed using an automated hemocytometer (IDEXX ProCyte Dx Hematology Analyzer, IDEXX Laboratories, Westbrook, ME) to determine complete blood count variables. Blood serum was analyzed using an automated analyzer (IDEXX Catalyst Dx Chemistry Analyzer with an Equine 15 CLIP, IDEXX Laboratories), and fibrinogen was determined via IDEXX VetAutoread (IDEXX Laboratories). Fecal samples were submitted to a commercial laboratory (Molecular Research LP, in Shallowater, TX) for DNA sequencing and
microbiome analysis. There was no effect of treatment × day interactions for hematology parameters (red blood cell concentration, P = 0.86; white blood cell concentration, P = 0.69; neutrophils, P = 0.59; glucose, P = 0.43; and fibrinogen, P = 0.90). There was an effect of day observed on red blood cell concentration (P < 0.001), white blood cell concentration (P = 0.04), neutrophils (P = 0.03), and fibrinogen (P = 0.02). In addition, there was an effect of treatment (P = 0.02) on fibrinogen. Clostridia and bacteroidia were the most abundant bacteria found in fecal samples of the foal and dam pairs. There was no effect of treatment × day interaction on clostridia (P = 0.24) or bacteroidia (P = 0.35). However, there was a main effect for day (P < 0.001) noted for relative abundance of each bacterium. Although present in very small amounts (< 1%), fibrobacteria was the only class of bacteria to result in an effect of treatment × day interaction (P = 0.05). Bacterial flora became more diverse and similar to the matched dam sample after the completion of any antibiotic treatment. Further research is needed to determine the role specific antibiotics play in the neonatal foal and if antibiotic use has any affects that might carry into adult life. In addition, continued microbiome studies could lead to microbiome analysis being involved in diagnostics.



amikacin, bacteroidia, ceftiofur, clostridia, fibrobacteria, microbiome, penicillin


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