Equine hospital data as a source for study of prevalence and heritability of osteochondrosis and palmar/plantar osseous fragments of Swedish Warmblood horses.

REASONS FOR PERFORMING STUDY: Disturbances in skeletal development, primarily osteochondrosis (OC) and palmar/plantar osseous fragments (POF), have been commonly reported as problems in young horses. However, there are few reports of such findings for epidemiological analyses or breeding purposes. OBJECTIVES: To evaluate equine hospital data as a possible source of information for genetic evaluations by estimating prevalence and heritability of OC in the stifle, hock and fetlock joints and of POF in the fetlock. METHODS: Data on Swedish Warmblood (SWB) horses were obtained from a large equine hospital in south Sweden. Prevalences were based on radiographic examinations of 879 screened horses, mainly evaluated as part of a prepurchase examination and 3639 horses with a reported history of orthopaedic problems. For the heritability study the 2 data sources were pooled and 3199 examined horses with pedigree information were considered for the linear animal model analyses. RESULTS: The overall prevalence of OC was 13% (stifle 9%, hock 6% and dorsal osseous fragments in fetlock [DOF] 10%) and POF 10%. The overall heritability of OC was 0.05 on the visible binomial scale. The corresponding heritabilities for OC in the stifle were 0.03, hock 0.08, DOF 0.10 and POF 0.13. These values correspond to heritabilities of 0.09-0.38 on the underlying quantitative scale. CONCLUSIONS AND POTENTIAL RELEVANCE: Obtained prevalences and heritabilities were in accordance with other studies, supporting the hypothesis that data regularly obtained from equine hospitals may be a valuable source in studies of inherited disorders such as OC and POF. There is a need for more standardised documentation of diagnoses and consistent recording of identity of examined horses using passports or breed databases. Compilation of results from major clinics is desired in order to cover most progenies of stallions used in a region or nation.

Mapping quantitative trait loci for principal components of bone measurements and osteochondrosis scores in a wild boar x large white intercross.

Data on osteochondrosis and femur dimensions from 195 F2 pigs from a wild boar x Large White intercross were analysed with the aim of detecting quantitative trait loci (QTLs) for normal and disturbed bone formation. The information from numerous recorded traits was summarized by principal component analysis and analysed by least-squares interval mapping. An increase in the proportion of wild boar alleles across the genome increased length versus width of femur and reduced the prevalence of osteochondrosis. The presence of QTLs with an impact on femur dimensions was indicated on chromosomes 2, 4, 16 and 17 and on osteochondrosis on chromosomes 5, 13 and 15. A substantial effect of the chromosome 5 QTL calls for further studies within commercial populations to evaluate whether marker-assisted selection could be used to reduce the prevalence of osteochondrosis.

Development of the genital peritoneal folds in sheep.

Development of the genital peritoneum in the sheep was studied in embryos/fetuses that were 27-69 days old. The plica mesonephrica was the first visible fold of the urogenital organs of the embryos and was the origin of the proximal mesorchium or mesovarium. The plica suspensoria gonadalis fixed the gonad to the mesonephros and held the cranial genital ligament and the cranial part of the gubernaculum. The distal and the cranial part of the gernaculum. The distal mesorchium or mesovarium evolved from this fold. The inguinal fold fixed the caudal part of the gubernaculum. The suspensory fold of the gonad and plica inguinalis formed a system of serosal folds called the Plica gonadoinguinalis. The fold of the genital ducts had two parts, divided by the crossing with the gubernaculum. The mesepididymis or mesosalpinx evolved from the cranial part of the fold, while the caudal part was the origin of the mesoductus deferens or mesometrium. The caudal part of the right and left folds contributed to defining another system of peritoneal folds, the Plica genitalis. A rearrangement of some accepted terms in the nomenclature is proposed, as are some new terms. An analysis of the meaning of some terms, especially those applied to systems of peritoneal folds, is given to aid in their interpretation.

Osteochondrosis in wild boar-Swedish Yorkshire crossbred pigs (F2 generation).

Osteochondrotic lesions occur in very high frequency in growing pigs of all commercial breeds and are claimed to be associated with high growth rate, and not to occur, or to be milder, in slow-growing pigs. The present study monitored the magnitude and distribution of osteochondrotic lesions in a crossbred pig population of wild boar and Swedish Yorkshire ancestry. In this population, having a low growth rate, the distribution and extent of osteochondrotic lesions was similar to that of purebred Swedish Yorkshire pigs, and only weak relationships between the studied growth parameters and osteochondrosis could be found.

Locomotion and gait analysis.

Gait analysis can play an important role in exercise physiology, racetrack ergonomics, lameness prophylaxis, and assessment of performance potential in racehorses. This article concentrates on the methods used for gait analysis and considers some basic data on the different gaits of the horse.

Sacroiliac lesions as a cause of chronic poor performance in competitive horses.

The histories and clinical signs in 11 horses with longstanding poor performance attributed to chronic sacroiliac damage are described. The main clinical feature was a lack of impulsion from one or both hindlimbs causing a restriction in the hind gait or lowgrade lameness. A temporary improvement was often achieved using anti-inflammatory medication, but eventually all the horses were killed because of unsatisfactory progress at exercise. Post mortem examination revealed that changes were confined to the sacroiliac joints. The macroscopic and histological findings varied considerably and in only two cases could the changes be classified histologically as arthrosis. In the other nine horses there was increased joint surface area or irregular outline associated with extensions of the joint on the caudomedial aspect. These changes were interpreted as indicating a chronic instability of the joint leading to restriction of hindlimb impulsion. The underlying cause of the problem was not ascertained but the significance and possible pathogenesis of the lesions are discussed.

Treadmill for equine locomotion analysis.

A treadmill for equine locomotion analysis is described and its potential considered for locomotive research and clinical investigation. The treadmill comprised an endless belt driven by a hydraulic motor at various speeds up to 14 m/sec and the direction of belt movement was reversible. The carrying side of the belt ran over a steel-concrete table which acted as a flat support. The belt itself consisted of a steel base on to which was glued a rubber belt and the surface was covered with a layer of coir matting which permitted some forward sliding of the landing hooves simulating the conditions on an ordinary track. The treadway could be inclined up to 10 degree in the longitudinal and 7.5 degrees in the transverse direction. To minimise the risk of injuries a special emergency stop system was installed. Horses adapted well to exercising on the treadmill, even without any previous experience. A good correlation was found between the gait repetitiveness on the racetrack and that displayed on the treadmill. One horse recorded both on the racetrack and on the treadmill showed significantly shorter strides on the treadmill but this did not invalidate the treadmill as a useful research tool in the study of equine locomotion.

Effect of induced back pain on gait and performance of trotting horses.

Back pain was induced in Standardbred horses by multiple intramuscular injections of a concentrated lactic acid solution into the left longissimus dorsi muscle. The investigation was divided into 2 parts. In Stage 1, 2 trotters were exercised on a treadmill and filmed by high speed cinematography before and after the induction of back pain. No signs of hindlimb lameness were evident and no quantitative changes in the components of the gait resulted, but a noticeable reduction was seen in performance capacity. Stage 2 involved a more intensive clinical and cinematic analysis of 3 horses. In these animals some changes were detected in the stride pattern, but no obvious gait disturbance was produced. The principal effect was stiffness in the thoracolumbar spine and an inability to perform at fast paces.

Natural rigaidity of the horse's backbone.

The functional anatomy of the thoracolumbar (TL) spine is considered in relation to the horse's ability to perform at speed and to jump. The morphological features quite clearly show the relative inflexibility of the equine back and this was confirmed by some experimental studies. Fresh post mortem specimens from 5 Thoroughbreds were used to estimate the limits of dorsoventral movement of the TL spine from mid-thoracic to the cranial lumbar (T10-L2). The individual spinous processes could be moved a mean 1.1-6.0 mm on maximum ventroflexion and 0.8-3.8 mm on dorsiflexion. The overall flexibility of the back was found to be 53.1 mm. Caudal to the mid-point of the back (T13) there was virtually no lateral or rotatory movement of the spine possible. The pathogenesis of some of the common causes of back trouble are discussed including the so-called vertebral subluxation and its treatment by chiropractic manipulation. From an anatomical viewpoint, this condition appears to be a misnomer and may simply be attributable to muscular imbalance leading to aspastic scoliosis.

The application of high-speed cinematography for the quantitative analysis of equine locomotion.

Locomotive disorders constitute a serious problem in horse racing which will only be rectified by a better understanding of the causative factors associated with disturbances of gait. This study describes a system for the quantitative analysis of the locomotion of horses at speed. The method is based on high-speed cinematography with a semi-automatic system of analysis of the films. The recordings are made with a 16 mm high-speed camera run at 500 frames per second (fps) and the films are analysed by special film-reading equipment and a mini-computer. The time and linear gait variables are presented in tabular form and the angles and trajectories of the joints and body segments are presented graphically.

Equine locomotion; 1. The analysis of linear and temporal stride characteristics of trotting standardbreds.

The movements of the individual limbs of 30 clinically sound Standardbred trotters were studied using high-speed cinematography. At a speed of 12 metres per second (m/sec; 1:23.6 min/km) the mean stride length was 545 cm and the mean duration of the stride was 455 milliseconds (msecs). The stance phase in the forelimbs was 100 msecs and 177 msecs in the hindlimbs. This difference was due to a longer restraint period in the hindlimbs and resulted in slightly shorter swing phases for the hindlimbs. The variations in any particular horse for stride length and for the duration of stride, stance, swing and propulsion were very small (variation coefficient: approximately 2 per cent). For the restraint stage, however, the variation coefficient was around 5 per cent. The variations noted between different horses were generally 2 to 3 times greater than those recorded for the same horse. There was a close correlation between stride and swing phase duration, suggesting that the swing phase was the main contributor to the stride-time variations of different horses trotting at the same speed. The restraint and propulsion stages did not seem to play an important role in this respect for this group of animals.

Equine locomotion: 2. The analysis of coordination between limbs of trotting standardbreds.

A high-speed cinematographic analysis of interlimb time and linear gait characteristics was carried out at racing speed (12.0 m/sec; 1:23.6 min/km) in 30 clinically sound Standard-bred trotters. In respect of the whole group of horses the racing trot was found to be a very regular and symmetric gait. The variation coefficient between different horses ranged from 8 to 21 per cent depending on the particular characteristic being investigated. The variations recorded in individual animals were about 60 per cent less than those found for the whole group. The most stable characteristics were the duration and length of the step. Some horses exhibited striking gait asymmetries and the possible causes are considered. It is also observed that some trotters adopt a transition of gait that cannot be classified as a trot.

Equine locomotion: 3. The reproducibility of gait in standardbred trotters.

The reproducibility of certain gait characteristics was investigated in Standardbred trotters at a speed of 12.0 m/sec. Twenty-two horses were recorded twice on the same day and 4 of them on a third occasion 3 years later. The short-term reproducibility was shown to be very good. In the long-term study it was found that the stride length and duration of swing and stride had increased. This was interpreted as an effect of training.