History and tradition

Much has been written about the conformation of the horse during the past 200 years, but very little is based on research. This does not mean that the work is of less interest. It is thought provoking that many of the relationships between conformation and performance described by Bourgelat (1750) and Magne (1866) correspond well with the results from recent research. They stressed the importance of the hindquarter conformation. Horses with hind limbs placed well underneath themselves were found suitable for dressage work, whereas those with hind limbs camped out behind were likely to show good speed. Another early author, Hörman (1837), wrote that a long and forwardly sloping femur facilitates lifting of the hind limb and the horse’s ability to step under itself. Ehrengranat (1818) maintained that a sloping shoulder, long radius, short fore cannon and a flat croup are desirable for good movement. According to Schmidt (1928), a small hock angle means that, although the horse will be able to step under itself easily, it will not be able to carry weight on the hind quarters due to decreased strength in the hock. Thus, he regarded a normal hock angle as advantageous for the function of the hind limbs. Most authors of handbooks on conformation evaluation believe that a large hock angle leads to rigid and incorrect hind limb movements as well as an increased strain on the hind limb joints (Wrangel, 1911–1913; Forsell, 1927; Anon, 1940; Bengtsson, 1983). Much of these horsemen’s knowledge is still in practice but parts of it seem to have been forgotten in recent years.

In the practical situation, it often appears that the results from research based on both subjective evaluation and quantitative analysis has confirmed some and rejected other aspects of these old relationships. Some of the ‘forgotten’ relationships have also been rediscovered. Even though objective methods for conformation evaluation will probably play a more important role in the future, traditional subjective evaluation will always be important. It must be kept in mind that there are aspects of conformation that cannot be measured by objective methods.

Subjective evaluation

Traditional subjective evaluation of conformation is currently performed in many different ways. Almost every country has its own protocol. Furthermore, many breeds have their own specific regulations that instruct the judges how to judge according to the standards of the breed. A problem with traditional evaluation is that subjective evaluations of conformation vary greatly between judges, although some morphological characteristics are assessed more consistently than others (van Vleck & Albrechtsen, 1965; Grundler, 1980; Magnusson, 1985a; Van der Veen, 1996). It is obvious that the reliability of the evaluation is dependent on the skill and experience of the individual judge.

The importance of the traditional conformation evaluation also varies between breeds. In racehorses and Standardbred trotters, racing performance is the main parameter when selecting individuals for breeding. In riding horses intended for dressage and jumping, the selection is mainly based on conformation and performance tests carried out at 3–4 years of age. Since riding horses perform in competition much later in life than racehorses, it is desirable to have a method for prediction of breeding value in young stallions and mares that do not have any performance record. Because the selection of stallions in most countries is stepwise, and performance tests are only applied to those that reach minimum conformation standards, it is very important that conformation evaluation is based on correct criteria.

A step towards a more objective interpretation and analysis of subjectively obtained conformation scores is the so-called linear scoring system, in which trained members of the jury score the conformation of the horse relative to the mean of the population (Van der Veen, 1996). Thus, judging still remains subjective, but it is the interpretation and the analysis of the judges’ scores that becomes more objective. In the Netherlands this is done for the Warmblood (KWPN) as well as the Friesian (KFPS) horses at studbook admission (Fig. 11.1).

Quantitative analysis

Quantitative methods for measuring conformation can be used for an objective evaluation (Rossdale & Butterfield, 2006). Several studies have been carried out, especially on riding horses. The results do often show a great deal of conformity, but in most cases it is impossible to directly compare such parameters as angle measurements from different studies, due to differences in methods of measurement.

Quantitative conformational analysis, as a complement to the traditional evaluation, has been proven to increase the accuracy in the prediction of performance potential in young riding horses (Holmström & Philipsson, 1993). However, applying this knowledge in practice, i.e. in breeding evaluation programs, talent scouting, etc., has been very difficult. Much of the resistance to quantitative analysis is due to the deeply rooted tradition of subjective evaluations in the horse industry, combined with a lack of familiarity with the new methods. In addition, there are some shortcomings in the method itself. Obtaining quantitative measurements has, until recently, been a slow procedure – too slow to be incorporated into stallion tests and other similar events. New computerized methods have now been developed that will speed up the process and make it possible to measure many horses in a short time.

In recent years an objective method, developed in Sweden by Magnusson (1985a) for a study of Standardbred trotters, has been further developed and refined for use in the Thoroughbred racehorse industry in the USA (M Holmstrom and D Lambert, unpublished work, 2004). The method was originally based on reference points marked on the horse with small paper dots glued to the skin (Fig. 11.2), and when first used all measurements were registered ‘by hand’ from a picture projected on a wall using a simple measuring band and a protractor. Later the whole procedure was computerized and the measurements were obtained from a digital photo on a laptop computer. The measurements were registered by clicking with the mouse on the white markers. The computer then calculates all length and angle measurements (Fig. 11.3). In the most recent version joint angles and length and proportional measurements can be obtained from a picture with just one paper dot on the hip.

Conformation and growth

Conformation evaluation in young growing horses calls for an understanding of the effect of age, i.e. the effect of growth on the conformation. The accuracy of quantitative methods applied to foals and yearlings, with the aim of predicting future performance and soundness, are dependent on age adjustments according to reliable growth curves for each individual measurement. Growth curves for some body measurement such as height at the withers are mainly breed specific while many other growth curves are specific for the method used for measuring a trait. Thus, growth graphs obtained by one quantitative method cannot be used together with a different quantitative method.

Conformation, performance and soundness

Searching for talented young sport horses involves evaluation of many different qualities. Temperament, movement and jumping ability are of course the most important in riding horses, but the significance of conformation must not be neglected. Furthermore, dressage riders seek ‘good looking’ horses, with conformation that facilitates good movements, soundness and, above all, the ability to show a high level of collection. The competition results of Grand Prix horses are certainly dependent on the skill of their riders and trainers, but their conformation and movement must have the basic qualities that create the necessary conditions for successful training of the horse. Resistance from the horse is often interpreted as poor temperament but might just as well be due to pain or lack of ability to carry weight on the hind limbs caused by inappropriate conformation and/or movement. Potential world class Grand Prix dressage horses are difficult to find because many promising young horses with excellent gaits fail to learn passage, piaffe and other collected movements, resulting in years of wasted training. The ability to collect and work in balance is also very important in a jumping horse.

Conformation is also important in the selection of most other performance horses including Thoroughbred racehorses and Standardbreds. However, a successful use of conformation as an indicator of performance requires good knowledge of the relationships between conformation and performance, as well as a reliable method for its evaluation. In most cases a subjective evaluation is not sufficient. Many important variables are almost impossible to judge correctly without objective measurements.

This chapter will focus on objective measurements and subjective conformational characteristics that are important for the function of sport horses and racehorses. For those who have a specific interest in the characteristics of a specific breed, that information can be obtained from the respective breeding organization.

Deviations of limb and toe axis

One important part of the subjective evaluation is to describe deviations of limb and toe axes, if any. The most common deviations are described in Figure 11.4. Deviations from the straight (normal) limb and toe axes have traditionally been considered as a considerable weakness. However, not all deviations from what has been the desired conformation should be judged as abnormal. About 80% of all Warmblood riding horses and Standardbred trotters had outwardly rotated hind limbs (Magnusson, 1985a; Holmström et al., 1990). The frequency of this ‘faulty conformation’ is so high that it must be regarded as normal. Boldt (1978) maintains in his dressage handbook that outwardly rotated hind limbs facilitate exercises such as half-pass and shoulder-in. In this context, it is important to distinguish between hind limb rotation and toe-out conformation as well as between rotated hind limbs and hind limbs that are narrow at the hocks (cow hocked). Confusion between these characteristics should be avoided, especially as the rotated hind limb conformation should be considered normal. To judge this aspect of conformation, the observer should stand behind the point of the hock rather than behind the tail of the horse. The latter position makes it impossible to see if the rotated hind limb is also narrow at the hocks.

Bench kneed conformation in the forelimbs together with a toe-in conformation is a very common type of deviation in riding horses, while outwardly rotated forelimbs are seldom seen in adult riding horses (Holmström et al., 1990). According to Magnusson and Thafvelin (1985a) the converse is the case in Standardbred trotters. This difference may partly be explained by the fact that trotters are narrower through the chest than the riding horses, even after adjustment for different height at the withers. Several other authors have also found that bench knee and toe-in conformation seems to be related to weight and width of the breast (Santschi et al., 2006; Firth et al., 1998). Santschi et al. (2006) studied the development of front limb deviations in foals and concluded that calf knee conformation in foals tends to self correct and eventually and it was also found that the incidence of bench knee increased between the age of 1 week and 18 months. Anderson et al. (2004) compared conformation to injury in Thoroughbreds and found that calf knees were somewhat protective agains injuries. Today most clinicians feel that mild carpal valgus is protective and is actually normal during growth.

As in the hind limbs, there is often confusion between outwardly rotated forelimbs and a toe-out conformation. Even though bench knee conformation in a riding horse does not have any documented negative effects on the long-term performance, bench kneed horses have been reported to have a higher frequency of splints on the medial side of the third metacarpal bone (Adams, 1974; Davidson, 1970; Nordin, 1980).

The frequency of toe-in and/or bench knee conformation, as well as of most other deviations, was the same among the elite dressage horses and show jumpers as in a group of riding school horses (Table 11.1). This indicates that mild-to-moderate deviations from the ‘normal’ limb conformation do not impair either soundness or performance in riding horses. However, it is important to emphasize that, even though mild and moderate deviations can be accepted, severe deviations of any type should be considered as a major weakness. Several authors have claimed that there is an increased stress to the distal parts of the limbs in horses with toe-out and toe-in conformation (Churchill, 1962; Rooney, 1968; Beeman, 1973; Magnusson, 1985c). This can often be noticed as synovial distensions of the fetlock and the coffin joints, as well as swelling of the distal metacarpal growth plate.

According to Adams (1974), calf knee (back at the knee) conformation may predispose to lameness, whereas buck knee (over at the knee) conformation is less serious. This is probably true for Standardbreds as well as Thoroughbred racehorses that overextend the carpal joint considerably during the midstance phase. Steel et al. (2006) reported that carpal lameness occurred in 28% of a group of Standardbred horses and was present in 56% with forelimb lameness. Of the variables studied, poor forelimb conformation and more intense speed training were predisposing factors. Back et al. (1996) proved in Warmbloods that there is a relationship between a calf knee conformation at square stance and carpal hyperextension at trot.

Head, neck and body

Many of the criteria that are used to describe the head, neck and body are very difficult or impossible to analyze objectively. Such criteria are type, the setting of the neck, the shape of the withers, the ‘harmony’ of the horse, etc. They have to be evaluated subjectively. Other characteristics, such as length of the neck and body or height at the withers, can be objectively measured or subjectively scored (Van der Veen, 1996).

It is obvious that there are significant relationships between head, neck and body characteristics and performance, which are reflected in the difference between, for example, a slow, heavy draught horse and a fast, elegant racehorse. Thus, differences between breeds have, to a large extent, originated from different demands upon the horses. However, within a certain breed it is much more difficult to correctly describe and evaluate the relatively subtle differences, and this difficulty has been associated with a rather large variation between judges (van Vleck & Albrechtsen, 1965; Grundler, 1980; Magnusson, 1985a). Long experience, a deep understanding of the influence of conformation on performance and, when appropriate, inclusion of objective measurements can minimize these discrepancies. Figure 11.5 shows two horses, one with a low set neck and the other with a well set neck.

In handbooks on evaluation of the conformation of sport horses, some characteristics are described more consistently. A long and well-set neck are considered important for most kinds of performances (Wrangel, 1911–1913; Forsell, 1927; Anon, 1940; Boldt, 1978; Bengtsson, 1983) and a long well-developed withers is said to be important for horses that are working under saddle (Van der Veen, 1996). In a large, cohort study of a Warmblood population, in which linear scoring results collected at studbook admission were related to later performance in dressage and show jumping, it appeared that when horses were genetically selected on height at the withers, neck length was shorter. Longer necks were genetically related to a conformation more suited for dressage performance but had less impact on jumping performance (Ducro et al., 2009a).

In contrast, results from objective studies show that elite show jumpers have significantly longer necks than elite dressage horses and ‘normal’ horses (Holmström, unpublished data) (Table 11.2). Other studies showed significantly shorter necks in elite dressage horses than in other riding horses but there was no significant correlation between the length of the neck and gaits under saddle in 4-year-old riding horses (Holmström et al., 1990; Holmström & Philipsson, 1993). Available objectively obtained results indicate that a long neck might be an advantage for jumping horses, probably because it makes it easier for the horse to maintain balance over the fence. In dressage horses, the setting of the neck is probably more important than its length (Van der Veen, 1996). It is generally agreed among riders and trainers of riding horses that a low set neck makes it very difficult to work the horse in a proper frame. However, there are no data supporting this statement, mainly because of the difficulties of objectively measuring the setting of the neck.

In Thoroughbred racehorses the length of the neck is part of the overall subjective conformation evaluation of young stock. The general opinion is that sprinters should have shorter necks than stayers but objective analysis of 780 grade 1 and group 1 winners in the USA and Europe showed that on both dirt and turf the sprinters, i.e. distances up to 7 furlongs, had slightly longer necks compared to the rest of the grade 1 and group 1 winners (M Holmstrom, unpublished work, 2009). The differences were small but statistically significant.

The setting of the head to the neck is also of importance (Van der Veen, 1996). A wide throat latch has always been considered important in racehorses, Standardbred trotters and Quarter Horses because it is said to facilitate breathing. In dressage horses, a wide distance between the wing of the atlas (first cervical vertebra) and the posterior ridge of the mandible has been considered important by riders. In a study of differences between elite dressage horses, elite jumping horses and ‘normal’ horses it was found that both the dressage horses and the jumpers had significantly greater width in this area than other horses (Holmström, unpublished data). A possible explanation is that a small distance might cause problems, most likely a mechanical resistance, at higher levels of collection when the horse is required to perform a maximal flexion at the poll.

Height at the withers has been linked to jumping performance in several studies (Neisser, 1976; Langlois et al., 1978). Müller and Schwark (1979) found that show jumpers were taller at the withers than dressage horses. Even though there is a positive correlation between height at the withers and jumping performance up to a certain limit (around 172 cm), it must be remembered that there is a great variation among elite show jumpers. The range of the height at the withers was between 158 cm and 178 cm in a study of the World Cup finalists in 1997 (Holmström, unpublished data). According to Ducro et al. (2009a) height at the withers was genetically related to dressage ranking but not to jumping ranking.

It is generally agreed that height at the withers is not related to stride length in different gaits (von Wagener, 1934; Krüger, 1957; Dušek et al., 1970; Dušek, 1974). However, Holmström and Philipsson (1993)

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