Antimicrobial therapy in neonatal foals

There are several differences in treatment of neonatal foals with antimicrobials, compared to mature horses. Firstly, the dose of many antimicrobials is different in the foal. For orally administered drugs, this may also affect their efficacy, due to different enteral absorption. Secondly, neonatal foals are not yet hindgut fermentors and this allows antimicrobials with a high propensity to cause colitis in mature horses to be used. Thirdly, toxicities are different and some antimicrobials used in mature horses, such as enrofloxacin, are not suitable for use in foals. Foal-specific information is therefore needed for their safe and effective treatment with antimicrobials.     

Suspected primary lactose intolerance in neonatal foals

The intestine of neonatal mammals must be able to secrete lactase enzyme to hydrolyse lactose in its mother's milk. Failure to secrete lactase results in failure to digest lactose. This results in osmotic diarrhoea, weight loss, failure to thrive, lethargy, colic and abdominal distension. Lactose intolerance may occur secondarily to intestinal bacterial infection. Primary lactose intolerance is recognised in human infants. Here we report 2 cases of suspected primary lactose intolerance in foals. The foals responded well to oral administration of exogenous lactase enzyme.     

Systemic antimicrobial therapy in foals

Antimicrobial agents are commonly used in neonatal foals for the treatment or prevention of sepsis. However, due to concerns about the development of antimicrobial resistance and increasing pressure on veterinarians to rationalise antimicrobial use, we should be trying to reduce the unnecessary use of antimicrobials. This article reviews many of the important considerations when selecting an antimicrobial for use in neonatal foals. Firstly, we consider general differences in neonatal pharmacology and physiology. Secondly, we review common antimicrobial drugs and their indications. Finally, we review antimicrobial stewardship.     

Colic and diaphragmatic hernias in neonatal foals

Colic in neonatal foals is common and unusual causes of colic are not rare. The case reported in this issue by Tapio et al. (2012 ) is a good example of an unusual cause of neonatal colic which presents both a diagnostic challenge and unusual consequences. Gastrointestinal disease, especially colic, ranks as one of the most common reasons why foals require veterinary attention during their first week of life, beyond the initial post natal examination. Foals with colic present a special diagnostic challenge, especially to the practitioner who might not have extensive experience in neonatal medicine. With the often rapid progression of neonatal diseases it is important to make a rapid and accurate assessment.     

Cochet-Bonnet aesthesiometer-determined corneal sensitivity in neonatal foals and adult horses

Corneal touch threshold (CTT) was measured in sick neonatal foals, healthy foals, and healthy adult horses with a Cochet-Bonnet aesthesiometer. The mean overall CTT for the adult horses, sick foals, and healthy foals was 4.82 +/- 0.87 cm, 3.21 +/- 0.24 cm, and 5.01 +/- 0.61 cm, respectively. The central cornea of adult horses was more sensitive than the limbal cornea. Corneal sensitivity was significantly reduced in sick neonatal foals compared to adults. The mean Schirmer I tear test values were significantly lower in foals than adults, and were 14.2 +/- 1.0 mm, 12.8 +/- 2.4 mm, and 18.3 +/- 2.1 mm wetting in sick neonatal foals, normal neonatal foals, and adult horses, respectively. Reduced corneal sensation and lower tear production may be associated with ulcerative keratitis and slow corneal healing in some foals.     

Oral and intravenous immunoglobulin therapy in neonatal foals

Newborn foals, deprived of colostrum and its rich supply of immunoglobulin G (IgG), were supplemented both orally and intravenously with purified equine immunoglobulin G (Lyphomune^®). Data were obtained from 18 foals given oral administration of IgG at Colorado State University and 26 foals given IgG intravenously at the Jockey Club de Sao Paulo in Brazil.Oral administration of 10-gm doses of Lyphomune^® in 18 colostrum-deprived Arabian foals, at various intervals within the first 24 hours after birth, resulted in increased serum concentrations of IgG. Administration of one 10-gm dose of Lyphomune^® immediately following birth provided a mean serum IgG level of 125 mg/dl after two hours. The recommended dosage of two 10-gm doses per 15 kg of body weight produced mean IgG serum concentrations of approximately 400 mg/dl by 14 hours. It was determined that an early bolus of IgG was most effective, although administration at any period during the first 24 hours would increase IgG levels significantly and in direct relationship to grams of Lyphomune^® administered.After the 24-hour study period, colostrum from each respective mare was provided by bottle feeding (200 ml) to 10 of the foals that were then allowed to nurse their dams normally. Significant increases in circulating IgG were observed in nine of these ten animals at four and eight hours after colostrum administration. No interfering effect was noted when colostrum and Lyphomune^® were given to the same foal.Intravenous administration of 10-gm doses of Lyphomune^® in Thoroughbred foals, immediately after birth, resulted in serum concentrations of IgG of 200–300 mg/dl six hours later. A second intravenous dose, at six hours after the initial dose, resulted in an additional average increase of 184 mg/dl. Four of six foals administered 10 gm of Lyphomune^® for each 15 kg of body weight reached serum concentrations greater than 400 mg/dl. It was demonstrated that Lyphomune^® was able to increase circulating levels of IgG, by either oral or intravenous administration, to levels considered protective in the newborn foal.     

Preliminary evaluation of hemostasis in neonatal foals using a viscoelastic coagulation and platelet function analyzer

Objectives – To compare coagulation and platelet function parameters measured using a viscoelastic analyzer in 3 groups: foals presenting to a neonatal intensive care unit with presumed sepsis, normal foals, and adult horses. Design – Preliminary prospective trial. Setting – Veterinary teaching hospital. Animals – Ten clinically healthy foals, 13 clinically healthy adult horses, and 17 foals sequentially admitted for suspected sepsis. Intervention – A single citrated (3.8%) blood sample collected at admission was submitted for coagulation evaluation using a viscoelastic analyzer. Measurements and Main Results – Time to initial clot formation (ACT), clot rate (CR), platelet function, and time to peak parameters were collected from the signature generated with the associated software. Peak clot strength was collected manually from signature tracings. Signalment, presenting complaint, blood culture results, clinical progression, and outcome were collected from the medical record. Kruskal‐Wallis testing was used to determine differences in coagulation parameters between groups, as well as to identify any associations between coagulation variables, foal variables, and outcome. Normal foals were more likely to have increased platelet function (P=0.04) compared with normal adult horses. Prolonged ACT (P=0.004) and decreased CR (P=0.03) were associated with foals with positive blood culture. There was a trend toward prolonged ACT and increased likelihood of death (P=0.06). Conclusions – Healthy foals differ in values measured by the viscoelastic coagulation and platelet function analyzer compared with healthy adult horses. ACT and CR abnormalities were more likely to be observed in foals with positive blood cultures. The viscoelastic coagulation and platelet function analyzer may be useful in identifying early hemostasic and platelet dysfunction in critically ill foals, particularly those that are septic.     

Controversies in therapy of infections caused by Rhodococcus equi in foals

Pneumonia caused by Rhodococcus equi is one of the most important causes of disease and death in foals. R. equi can also be cultured from a large variety of extrapulmonary sites of infection. In the absence of an effective vaccine, ultrasonographic screening for early detection of pulmonary lesions has become routine practice at many farms endemic for pneumonia caused by R. equi. Consequently, the most frequently recognised form of R. equi infection at such farms is a subclinical form in which foals develop sonographic evidence of peripheral pulmonary consolidation or abscessation without necessarily manifesting clinical signs. Evidence exists that not all foals with ultrasonographic lesions will progress to develop clinical signs, and treating a large proportion of foals based on subclinical ultrasonographic findings has been linked to emergence of macrolide‐ and rifampin‐resistant R. equi at a horse farm. Selectively treating only those foals with larger lesion scores and monitoring foals with daily physical inspections and weekly thoracic ultrasonography offers an approach that could decrease antimicrobial drug use without significantly increasing mortality. Current evidence continues to support the combination of rifampin with a macrolide (azithromycin, clarithromycin or erythromycin) for treating clinical infections caused by R. equi despite recently described pharmacological interactions between these drugs. When infection with a macrolide‐resistant isolate is confirmed, limited effective alternatives exist.     

The effect of omeprazole paste on intragastric pH in clinically ill neonatal foals

REASON FOR PERFORMING STUDY: Administration of omeprazole paste per os to healthy neonatal foals has been shown to effectively increase intragastric pH, but has not been evaluated in sick neonatal foals. OBJECTIVES: To determine the effect of orally administered omeprazole paste on intragastric pH in clinically ill neonatal foals requiring nasogastric intubation. METHODS: Intragastric pH was measured continuously for 24 h using an indwelling electrode and continuous data recording system in hospitalised neonatal foals age < or =2 days. Intragastric pH was measured for 12 h prior to (pretreatment period) and 12 h following (post treatment period) treatment with omeprazole paste (4 mg/kg bwt per os). All foals displayed periods of acidity (pH <4) prior to treatment. Statistical analysis compared pre- and post treatment mean and median intragastric pH, and percentage of time below pH 4. RESULTS: Eight foals were evaluated age 1-3 days, a gestational age of at least 320 days or reported to be full term. The mean (3.19 +/- 1.50 vs. 6.20 +/- 0.93) and median (4.6 +/- 1.7 vs. 6.86 +/- 0.89) pH were significantly higher and the percentage of time below pH 4 (32.25 vs. 1.1%) was significantly lower in the post treatment compared to the pretreatment period. CONCLUSION: Omeprazole paste effectively increases intragastric pH in clinically ill neonatal foals after one dose at 4 mg/kg bwt orally.     

Neutrophilic myeloperoxidase index and mean light absorbance in neonatal septic and nonseptic foals

Background: Two neutrophilic indices reported by the ADVIA 120 Hematology Analyzer, neutrophilic myeloperoxidase index (MPXI), and mean light absorbance (neutrophil X mean [NXM]) have been proposed as indicators of systemic inflammatory disease in horses and of neutrophil activation in coronary ischemic syndromes in people. Objective: The aim of this study was to evaluate NXM and MPXI in healthy, sick nonseptic, and sick septic foals to determine whether conditions likely associated with neutrophil activation result in decreases in these variables. Methods: In this retrospective study, CBC data from 61 neonatal foals presented to the Equine Teaching Hospital of Barcelona were evaluated for correlations between MPXI, NXM, percentage of large unstained cells, neutrophil count, and percentage of band neutrophils. Results obtained in septic (n=32), sick nonseptic (n=22), and healthy foals (n=7) were compared. In addition, results recorded in septic/neutropenic (n=12), septic/non‐neutropenic (n=20), nonseptic/neutropenic (n=8), nonseptic/non‐neutropenic (n=14), and healthy foals (n=7) were also compared. Results: A weak negative correlation was found between MPXI and neutrophil count and between NXM and percentage of band neutrophils. Septic/neutropenic foals had significantly higher MPXI values (median 17.9, minimum–maximum 4.7–42.5) than did septic/non‐neutropenic (1.5, ?24.4 to 22.3), nonseptic/neutropenic (6.6, 0.6–17.9), and nonseptic/non‐neutropenic foals (8.8, ?10.1 to 16.8) but did not differ significantly from controls (12.8, ?8.5 to 20.4). Conclusions: Significant differences in NXM or MPXI were not found when disease groups were compared with controls; however, septic/neutropenic foals had significantly higher median MPXI than other groups of sick foals. Further prospective studies are needed to clarify if this finding is related to decreased neutrophil function or activation in septic/neutropenic foals.     

Determination of cardiac output in neonatal foals by ultrasound velocity dilution and its comparison to the lithium dilution method

Objective – To compare cardiac output (CO) measured by use of lithium dilution (LiDCO) and ultrasound velocity dilution (UDCO) in conditions of high, intermediate, and low CO in anesthetized foals.
Design – Original prospective study.
Setting – University teaching hospital.
Animals – Six foals 1–3 days of age (38–45 kg).
Interventions – Neonatal foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, and CO. The CO was measured by use of LiDCO and UDCO techniques. Measurements were obtained from each foal at baseline and during low, intermediate, and high CO states. Measurements were converted to cardiac index (cardiac index=CO/body weight) values for statistical analysis. Agreement between the 2 methods was determined using Bland and Altman analysis and concordance correlation coefficients.
Measurements and Main Results – LiDCO determinations of CO ranged between 4.0 and 14.0 L/min resulting in cardiac index ranging between 75.5 and 310 mL/kg/min. There was no significant effect of blood pressure variation on bias or relative bias ( P =0.62 and 0.93, respectively). The mean bias and relative bias of UDCO (±SD) compared with LiDCO were −20.1±39.2 mL/kg/min and −7.7±23.4%, respectively. Concordance correlation coefficient between LiDCO and UDCO was 0.833.
Conclusions – When compared with LiDCO, the UDCO technique has acceptable clinical utility for measuring CO in healthy anesthetized newborn foals.