Original Research
Evaluation of Indicators of Weight-Carrying Ability of Light Riding Horses

https://doi.org/10.1016/j.jevs.2007.11.008Get rights and content

Abstract

To answer the question of whether horse height, cannon bone circumference, and loin width can be used as indicators of weight-carrying ability in light horses, eight mature horses underwent a submaximal mounted standard exercise test under four conditions: carrying 15, 20, 25, or 30% of their body weight. Heart rate was monitored, plasma lactate concentration was determined in jugular blood samples pre-exercise, immediately post-exercise, and 10 minutes post-exercise, with serum creatine kinase activity determined at the same times as plasma lactate concentrations, with additional samples collected at 24 hours and 48 hours post-exercise. Muscle soreness and muscle tightness scores were determined using a subjective scoring system 24 hours before and 24 hours after exercise. Heart rates remained significantly higher when the horses carried 25 and 30% of their body weight. Plasma lactate concentrations immediately and 10 minutes after exercise differed when horses carried 30% of their body weight compared with 15, 20, and 25% weight carriage. Horses tended to have a greater change in muscle soreness and muscle tightness when carrying 25% of their body weight, and a significant change in soreness and tightness scores was found in horses carrying 30% of their body weight. Loin width and cannon bone circumference were found to be negatively correlated to the changes in muscle soreness and tightness scores. In conclusion, the data suggest that horses with wider loin and thicker cannon bone circumference became less sore when carrying heavier weight loads.

Introduction

The optimum weight a horse can safely carry depends on a variety of physical traits. These may include the horse's size, conformation, body condition, age, duration of the work to be done, as well as speed at which the work is being performed. A few methods are used to help estimate how much weight a horse can safely carry; however, little research can be found to justify these methods.

Historically, the most common recommendation states that the total weight a horse can carry should not exceed 20% of the horse's body weight. This policy may have been based on the 1920 U.S. Calvary Manuals of Horse Management, where the recommended collective weight of rider and gear was not to exceed 20% of the total weight of the horses. Comparably, a more recent study of 360 endurance race horses, primarily of Arabian breeding, evaluated horse and rider weight relationships. They analyzed weight loads as horse body weight independent of rider weight, rider weight independent of weight of the horse, and a rider weight ratio calculated as rider weight divided by the weight of the horse. They concluded that conditioned horses were able to carry 20 to 30% of their body weight for 100 miles.1 In a follow-up study conducted by the same group of researchers, 193 endurance race horses were evaluated for weight loads as described in the previous study. They found that horses with increased body weight without a proportional increase in cannon bone circumference had increased incidence of biomechanical failure, for which the horse did not successfully complete the race.2

The amount of bone that a horse possesses also has been used as a method to help determine the amount of weight a horse can carry. There are a multitude of studies using the equine third metacarpal bone to evaluate skeletal biomechanics relationships, which include bone strength in relation to bone fracture, tension, stress, and elasticity.3, 4, 5 Ultrasound also is used as a tool for assessment of bone quality in horses6 and humans.7 Based on a study conducted by Bynum et al,8 a simple noninvasive method for evaluating the amount of bone is by measuring the circumference of the third metacarpal bone midway between the carpal−metacarpal joints, where the recommended circumference is estimated to be 20 cm per 454.5 kg horse body weight. Although this method does not evaluate the actual mineral content of the bone, which is the primary determinant of skeletal bone strength, it can be used as a quantitative measure of the amount of bone.

When evaluating weight-carrying ability of the riding horse, it is important to take into consideration the conformation of the horse. It was determined by a German scientist in 1941 that the horse carries approximately 60% of its body weight on its front legs and 40% on the hind legs; therefore, the center of gravity of a riderless horse would be located at a point just behind the withers near the heart girth.9 There are certain conformational qualities that make it easier for the horse to carry weight on its back. It is a widely held belief among top endurance competitors that loin width is a highly desirable quality in endurance prospects (personal correspondence). The loin of the horse is defined as the pivot point of the horse's back and is the area between the last rib and the croup (crest of the ilium). The width of the loin ends where the ribs start to curve downward. No studies have evaluated loin width as a possible indicator of weight-carrying capacity in the horse.

Plasma lactate concentrations and heart rate are reliable variables used to evaluate the workload of a horse.10 The activity of serum creatine kinase (CK) has been used as an indicator of muscle damage and the association of postexercise muscle soreness in humans.11 The objective of this study was to determine whether cannon bone circumference, loin width, and horse height could be used as indicators of the weight-carrying ability of the light riding horse.

Section snippets

Horses

Eight mature horses of light horse type were used, 1 mare and 7 geldings, age 6 to 18 years and weighing 391 to 625 kg. All horses were used as lesson horses but had been pasture rested for a period of 4 months before the study. During the study, horses were housed individually in 4 × 4 m stalls with daily turnout. All horses received a daily ration of timothy/alfalfa mixed hay (13.66% CP, DM; 8-10 kg/day) and a pelleted concentrate (14.18% crude protein, dry matter; 3 kg/day) divided between

Results

Table 1 shows the physical data for each horse. There were no changes in body weight during the study. Environmental temperature and relative humidity data for the exercise tests are shown in Table 2. A greater (P < .05) work rate was elicited when horses carried 25 and 30% of their body weight (Fig 1). Heart rates before exercise did not differ significantly among treatments (Table 3). Heart rates, respiration rates, and rectal temperatures differed (P < .05) when the horses carried 25% and

Discussion

To our knowledge this is the first study of this type. In this study, a subjective scoring system of assessment of muscle soreness and tightness was employed as a guide in the assessment of chosen variables of body weight, horse height, cannon bone circumference, and loin width on their usefulness as indicators of weight-carrying ability in light riding horses. The submaximal mounted standard exercise test of the current study was designed to simulate a 45-minute working session of an

Acknowledgments

This study was funded by The Research, Creative, and Other Scholarly Activities (RCOSA) grants.

References (21)

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