Prevalence of Elevated Temperatures Among Horses Presented for Importation to the United States

Long-distance transport of horses can result in stress and predispose horses to infections, particularly of the respiratory tract. Monitoring of body temperature is one means of detecting disease associated with long-distance travel. In this retrospective study, the prevalence of elevated temperature among horses arriving at United States air–ocean import centers was determined. The prevalence of elevated temperature in horses varied by import center as well as age and breed categories. The majority of elevated temperatures occurred at or within 12 h of arrival, typically as a single occurrence and usually as a low-grade elevation in body temperature (i.e., > 101.5°F but < 102.5°F). Determination of the specific causes of elevated temperatures, particularly the distinction between a stress response versus fever caused by infection, among this population of horses would require collection of additional data. Authors’ addresses: Department of Clinical Sciences, Colorado State University, College of Veterinary Medicine and Biomedical Sciences, 300 West Drake Road, Fort Collins, CO 80523 (Traub-Dargatz); and 2150 Centre Avenue, Building B, Fort Collins, CO 80526 (Bischoff); e-mail: [email protected].

1. Introduction

The importation of horses (the term horse will be used here to describe all equids, including horses, ponies, donkeys, and mules) into the United States is regulated by the United States Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services (USDA-APHIS-VS). Quarantine regulations are developed to reduce the risk of spread of infectious diseases and based on the status of the origin country for specified equine diseases. Other than those horses arriving for special events such as the World Equestrian Games, horses arriving by air or ocean are quarantined at one of three animal import centers: the New York Animal Import Center (NYAIC) in Newburgh, NY, the Miami Animal Import Center (MAIC) in Miami, FL, or the Los Angeles Animal Import Center (LA-AIC) in Los Angeles, CA. 

On arrival to the United States, horses are examined by USDA-APHIS-VS personnel to check documentation and evaluate health status, which includes collecting rectal temperature and blood samples for official testing. Horses must remain in USDA quarantine for the period determined by USDA, which is based on the disease status of the origin country. Typically, these quarantine periods are referred to as 3-, 7-, and 60-day quarantine periods. Details regarding import requirements can be found at the National Center for Import and Export website.¹ Historically, at least < 3 days were required to obtain regulatory test results; more recently, with expedited shipping of samples and reduced turnaround times at the laboratory, test results can be available in < 3 days. Although the tests may be available in < 3 days, all horses presented for import to the United States by air or ocean must remain in quarantine for a minimum of 42 h for observation. To be released from quarantine, horses must have negative results on the official tests, been held in quarantine for the specified period of time, and three non-elevated temperatures (< 101.5°F) recorded for the 24-h period immediately before release. During quarantine, horses are observed for clinical signs of disease and given a physical examination, including recording of rectal temperature, that is generally performed every 12 h.

Above-normal body temperature can be the result of a true fever (most often caused by an infection), inflammation, hyperthermia because of heat stress, drug reactions, allergies, tumors, or other causes; other causes, such as age, breed, previous experience with air travel, disposition, and location in the cargo area, might explain an increased risk for occurrence of elevated body temperature.²

To determine the prevalence of elevated body temperature among imported horses while in quarantine, the records for 4,720 horses were analyzed for this study. In addition, analysis of existing data was performed to determine factors associated with risk of an elevation in body temperature.

2. Materials and Methods

Individual records for horses imported over 1 calendar yr were retrieved from each center. The process for retrieval of data varied between centers depending on the type and availability of source documents (e.g., electronic or paper) in each center.

The study period for NYAIC and MAIC was calendar year 2008 and for LA-AIC, was calendar 2009. NYAIC and MAIC data for calendar year 2008 included at least four temperatures taken from each horse before release from quarantine. Data for calendar year 2009 were selected for LA-AIC, because before that time, the records included only entry and released body temperature recordings. Starting in January 2009, the LA-AIC records included at least four temperatures taken before release from quarantine.

NYAIC and MAIC are operated by USDA-APHIS-VS. LA-AIC import quarantine is a privately operated facility (Jet Pets, Inc.) with oversight by USDA-APHIS-VS; official records are maintained in the Los Angeles USDA-APHIS-VS office. Use of the term LA-AIC in this report refers to both Jet Pets, Inc. and the USDA-APHIS-VS Los Angeles office’s personnel that oversees import and quarantine of horses through Los Angeles.

Data about horses quarantined at NYAIC were collected from hard-copy records. Data about horses quarantined at MAIC were collected primarily from the Animal Quarantine and Examination System (AQES) electronic database; hard-copy records were reviewed for horses that had elevated temperatures to determine the treatment performed on these horses. Data (gender, age, breed, country of origin, date of arrival, and date of release) about horses quarantined at LA-AIC were available from a USDA-APHIS-VS electronic database (Import Tracking System); temperature and treatment information were retrieved from hard-copy records.

Variables available for analysis were body temperature on arrival and at intervals while in quarantine, age, breed, gender, purpose/use, country of origin, port of embarkation (departure airport for flight), port of entry (arrival airport for the flight), and dates of arrival and release. Certain variables were collapsed into a limited number of categories for analysis.

Horses that had a temperature >101.5°F any time from arrival to release from quarantine were categorized as having had an elevated temperature. Univariable logistic models were constructed to evaluate the effect of each risk factor on prevalence of elevated temperatures within each center. A p value of <0.05 was considered significant.

Within each center, multivariable logistic models were constructed with risk factors as independent factors. Backward elimination was used to eliminate factors with a p value > 0.05. Interactions between the factors were examined and if significant, were included in the final models.

A univariable logistic model was used to initially compare the prevalence of elevated temperatures between centers, with p values of < 0.05 considered significant. A multivariable model was constructed with import center, breed, age, and gender categories; region of origin, interaction with center, and other factors were included. The initial results of the multivariable model were used to determine the significance of the interactions. Separate models were to be constructed for each center if there was an interaction by center.

An initial three-center, multivariable logistic model with center, breed, age, gender, region of origin, four interactions between center, and other factors showed that all interactions with center were significant, meaning that the effect of all of these factors varies by center. Separate models were, therefore, constructed for each center.

3. Results

NYAIC

The NYAIC received horses through one of three airports (port of entry): JFK in Jamaica, NY, Newark in Newark, NJ, and Stewart at Newburgh/New Windsor, NY. [...]