Summary Twenty adult (5 to 14 years old) sedentary stallions of several breeds (8 Andalusians, 7 Arabians and 5 Anglo‐Arabians) were endurance‐trained for 3 months. Duplicate biopsies from 2 different depths (20 mm, superficial sampling site; 60 mm, deep sampling site) of the gluteus medius muscle were collected before and after training and after 3 months of detraining. Few significant changes in muscle fibre type composition were recorded in response to training. The percentage of type I fibres in the deep sampling site of the muscle in Andalusian horses and of type IIB oxidative fibres in the superficial region in Anglo‐Arabians had increased significantly (P<0.05) after training. The mean type I and IIA cross‐sectional area was increased significantly (range P<0.05 to P<0.0l) after 3 months' training in the deep site of the muscle in Arabian and Andalusian horses, but not in Anglo‐Arabians. The changes seen in fibre sizes disappeared after the detraining period. The mean number of capillaries adjacent to type I fibres in the superficial sampling site of the muscle had increased significantly (P<0.05) in response to training in Andalusian and Arabian horses. However, a significant decrease in the mean number of capillaries in contact with each fibre type relative to the mean area of that fibre type was observed associated with training in the deep region of the muscle for type I and IIA fibres in Arabians (P<0.01) and for type I fibres in Andalusian horses (P<0.05). It is concluded that a 3 month period of endurance training has a different effect on muscle morphology in different breeds. This period of training rapidly increases the size of the fibres with the greatest oxidative capacity (type I and IIA), particularly in the deep region of the gluteus medius muscle, but its intensity and duration were not sufficient to bring about a noticeable change in muscle fibre type composition and capillary density.

Mucoperiosteal exostoses (MpEs) of the tympanic bulla (TB), also referred as middle-ear otoliths, have been occasionally described in dogs and cats in association with clinical signs of otitis media or as an incidental finding, but they have not been recorded in other species. In this report, we describe the radiographic, gross, and histopathologic features of MpEs in 8 African lions (Panthera leo). All animals (5 males and 3 females) were adults that had been kept in captivity and had their skeletons conserved as part of an anatomic academic collection. A radiographic study revealed mineralized structures in the TB consistent with MpEs in 7 of the 16 examined TB; a computed tomography study identified MpEs in 12 of the 16 TB. Six TB from 4 lions were sectioned, and several MpEs were demineralized for histopathologic analysis. Grossly, MpEs appeared variable in number and shape. Some were globular structures that were loosely attached to the mucosal surface of the TB; others were isolated to coalescent bone spicules extending from the mucoperiosteum. Position was also variable, but MpEs frequently developed in the hypotympanum, especially on the ventromedial aspect of the TB wall. Microscopically, MpEs were composed of osteonal bone growing from the periosteum and not by dystrophic calcification of necrotic tissue debris, as is hypothesized in dogs. KeywordsAfrican lion, computed tomography, mucoperiosteal exostoses, middle ear, Panthera leo, pathology, tympanic bullaThe middle ear structure is well known in domestic animals, but it has only been occasionally studied in lions.6 Threedimensional anatomic reconstructions show that the middle ear of the lion and cat are similarly arranged but have large differences in absolute and relative size. 6,12 In mammals, the middle ear is lined by respiratory epithelium that is contiguous with the nasopharynx via the auditory tube; however, portions of the middle ear are lined by squamous to cuboidal epithelium, especially the petrous portion of the temporal and tympanic membrane. 1,12 In a recent exhaustive study on the histology and histopathology of the cat middle ear, Sula et al 12 introduced the term auricular mucoperiosteum to name this unique mucosal membrane lining the middle ear, which is characterized by the direct apposition of epithelia and submucosa with periosteal connective tissues.Little is known about the pathology of the middle ear in the majority of animal species. Infectious (bacterial) otitis media has been more frequently described in dogs, cats, and cows.7,12,13 Sula et al 12 recently described the histologic characteristics of diseased ears in a series of 50 cats and concluded that middle ear diseases in cats are far more common than gross lesions or clinical literature suggests.

The histochemical characteristics of skeletal muscle were assessed using a range of samples from 7 appendicular muscles taken from adult mixed-breed dogs (1.5 to 3 years of age). Two slow-twitch fiber subtypes (IA and IB) and three II subtypes (IIA, IIB and IIC) were identified according to myofibrillar myosin adenosine triphosphatase reaction after acid and alkaline preincubation. Type IIB fibers were not found in all muscles, and were only biologically significant in m. semitendinosus. The metabolic potential of these fibers is fairly similar to that of IIA fibers, but significantly different to that of IIB fibers in other mammals, suggesting that they may be designed to play a different functional role during locomotion. All canine muscle fibers have moderate to high oxidative capacity, which may be related to the extraordinary athletic capability of the species.

-The walk and trot at hand and at driving of five Andalusian Purebred stallions were studied by a 2D semiautomatic analysis system. Linear, temporal and angular variables from the right fore and hind limbs were obtained by using a 2D kinematic analysis system. In order to identify significant differences between handled and driving gaits, a paired Student t-test was performed. The swing period and the stride lengths of both fore and hind limbs and the overreach distance were lower at driving. Stride durations and Retraction-Protraction angle values in the hind limbs at trot did not differ under different conditions but scapular values at walk and trot, fore fetlock variables at trot and some of the stifle and tarsus parameters at walk and trot were modified by the use of the vehicle. It may be assumed that at fixed speeds driving horses try to maintain the stride duration of their natural gaits.

In the present investigation the right intracranial portion of the trochlear nerves and dorsal oblique muscle of the right ocular globe were removed from six adult dogs and analyzed by light and electron microscopy. Unmyelinated fibers were observed in the analyzed nerves. The number, diameter, area, and density of myelinated fibers were determined, as were corresponding axon area and diameter and myelin sheath thickness. Frequency histograms of myelin sheath thickness and fiber size show a bimodal distribution with a similar proportion of large and small fibers. Muscle samples were taken from the central portion of the muscle belly, subsequently frozen, cut, and stained with m-ATPase at pH 4.6. Fibers were classified as Type 1 or Type 2 according to their reaction to the m-ATPase and detailed morphologic and morphometric studies were made. The muscles showed two clearly distinct layers, a central layer and a peripheral layer, chiefly composed of Type 2 fibers. The fibers in the central layer were larger in size than those in the peripheral layer.