Development of the retinal circulation in the pig.

Retinal angiogenesis was studied in 300 eyes of 150 porcine fetuses by means of semithin histologic sections and vascular corrosion casts. In the embryonic and early fetal period, the retina is avascular and nourished via diffusion from the choriocapillaris and the vascular tunic of the lens. The development of the inner vascular plexus of the retina occurs in three different stages. In the first stage (angioblast phase), during gestational weeks 6-7, mesenchymal precursor cells arising from the arterial and venous circle around the optic nerve invade the nerve fiber layer of the retina via the otic disc border. They form a network of angioblasts that gives rise to an immature capillary network in the second stage (angiogenesis phase). This vascular monolayer is located within the nerve fiber layer and reaches the ora serrata around gestational weeks 9-10. Initially, the immature retinal capillaries have an irregular appearance with wide lumina and relatively small intercapillary meshes. Subsequently, the lumina become smaller by involution and atrophy. In the third stage (maturation and remodeling phase) the immature blood vessels differentiate into retinal arterioles, capillaries and venules. From gestational week 11 onwards, the larger retinal arterioles are surrounded by a distinct periarteriolar capillary-free zone. The three stages start at the optic disc and extend centrifugally towards the retinal periphery. The development of the outer vascular plexus is essentially different from the angiogenesis of the inner vascular plexus. The outer retinal vessels that are located in the inner nuclear layer arise from previously developed capillaries and venules located in the inner vascular plexus. Moreover, the development of the outer vascular plexus starts at the macula and proceeds along with the maturation of the neural retina.

The hyaloid vascular system of the pig. A light and scanning electron microscopic study.

The hyaloid vascular system of the pig was studied from 4 weeks of gestation until 2 weeks after birth by means of semithin sections and vascular corrosion casts. The vascular tunic of the lens is supplied by the posterior lens branches of the hyaloid artery (at the posterior lens pole), by the intermediate lens branches of the proper hyaloid arteries (at the lens equator) and by the anterior lens branches of the radial iridial arteries (at the anterior lens pole). Venous drainage takes place via the venous lens branches which leave the lens anteriorly and drain into the radial iridial veins. Regression of the vascular tunic of the lens occurs during the second half of fetal life and is nearly completed in the first postnatal days. The involution first affects the proper hyaloid arteries and their intermediate lens branches. Subsequently, the posterior lens branches regress, whereas the anterior lens branches in the pupillary membrane disappear in the perinatal period only.

Immunohistochemical detection of estrogen receptors in the canine uterus and their relation to sex steroid hormone levels.

Cyclic changes in estrogen receptor expression in the uterine tissue of 60 female dogs were evaluated, using an immunohistochemical technique on formalin-fixed paraffin-embedded sections. The expression of estrogen receptors in the uterine horns, body and cervix was quantified by means of an immunohistochemical score. A negative correlation was found between staining scores in the uterine horns and serum progesterone levels. Generally, staining scores in the uterine horns were highest during proestrus, declined during estrus and were lowest during early metestrus. During anestrus high staining scores for estrogen receptors were observed, indicating sensitivity for estrogens in a sexual quiescence stage. Compared with the uterine horns, high staining scores were found in the uterine body and cervix during estrus and metestrus. No positive staining for estrogen receptors was detected in 1 pregnant uterus. Fluctuations in estrogen receptors were more pronounced in endometrial stroma cells than in epithelial cells of the uterine horns. The importance of stromal cells in the sexual cyclicity of the canine uterus should not be underestimated when studying uterine endocrinology and pathology.

Immunohistochemical detection of progesterone receptors in the canine uterus and their relation to sex steroid hormone levels.

The aim of this immunohistochemical study is to describe the normal distribution of progesterone receptors in the various cell types of the canine uterine horns, body and cervix. The results can be used for research on uterine and endocrinological pathology, since the impact of progesterone on different uterine cell types is partly determined by the receptor availability. Nuclear staining for progesterone receptors was observed in epithelial cells of the surface epithelium, glandular ducts and basal glands of the endometrium, in endometrial stroma cells and in myometrial smooth muscle cells. This staining was positively correlated with the estradiol-17 beta:progesterone ratio, and reflects the positive effect of estradiol-17 beta and the negative influence of progesterone on the receptors. Staining scores were high during proestrus and decreased through estrus to early metestrus. In late metestrus, staining scores of the stromal and smooth muscle cells increased again. In anestrus, high scores of the surface-epithelial cells contrasted with minimal scores of the basal glands. This finding suggests a different hormonal regulation of the progesterone receptor expression in both epithelial cell groups. The higher staining intensities for progesterone receptors in stromal cells compared with epithelial cells might be explained by the fact that stromal cells mediate some effects of steroid hormones on the epithelial cells in the genital tract. Therefore, the role of stromal cells in regulation of the cyclic endometrial changes and in pathologic changes of uterine tissue should not be underestimated.

Flukicidal action of closantel against immature and mature Fasciola hepatica in experimentally infected rats and sheep.

The relative importance of peak level- and residual level-related flukicidal activity of closantel against immature and mature Fasciola hepatica was evaluated in a comparative efficacy trial using two animal species with a different plasma elimination pattern, that is, the rat and the sheep with an elimination half-life of less than one week and of two to three weeks, respectively. The rats were dosed orally with closantel at 20 mg kg-1 at two, four, six, eight and 10 weeks; the sheep at 10 mg kg-1 at eight, 10 and 12 weeks after artificial infection. Necropsy was performed either one week after treatment or 12 weeks after infection. Efficacy rates and the length of the recovered flukes were evaluated. It was demonstrated that the flukicidal effect of closantel is directly related to its peak plasma levels and less to its residual plasma concentrations. In the rat, a high efficacy (P less than 0.001) could be demonstrated against immature stages of four weeks or older. The two-week immature stages were less markedly affected. No significant differences in efficacy and size of the flukes were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection. In the sheep, the efficacy against six-week and eight-week-old immature stages varied between 70.3 and 76.8 per cent and between 92.8 and 96.5 per cent, respectively. As in the rats, no marked differences in efficacy were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinal vascular patterns in domestic animals.

In this paper a morphological study of the retinal vascular patterns in various species of domestic animals is reported. A classification of these patterns into four well-defined groups is described. In the domestic ruminants, pigs and carnivores the retina contains a compact plexus of blood vessels located in the major part of the light-sensitive portion of the retina (euangiotic or holangiotic pattern). In other domestic animals blood vessels are present only in a smaller part of the retina. In the rabbit, vessels are confined to a broad horizontal band coincident with the area of dispersion of the myelinated nerve fibres. The larger of these vessels are readily visible macroscopically (merangiotic pattern). In the horse and the guinea pig the retinal blood vessels are minute and restricted to the direct neighbourhood of the optic disc (paurangiotic pattern). The avian retina is completely avascular (anangiotic pattern), but a densely vascularised pecten oculi is attached to the linear optic nerve head and protrudes far into the inferior part of the vitreous body.

Anatomy of the ocular arteries in the horse.

Orbital and intrabulbar arteries were studied in 20 equine eyes by means of latex injections and methylmethacrylate casts. The orbital branches of the external ophthalmic artery arise far caudal to the posterior pole of the eyeball and present a variable topographic arrangement. The intrabulbar arteries are supplied by ciliary and choroidoretinal arteries. Dependent on their entrance into the eyeball, the ciliary arteries are subdivided into a posterior and an anterior group. The posterior ciliary arteries perforate the sclera post equatorially and consist of 4 major vessels that penetrate in the lateral, medial, dorsal and ventral meridian of the eyeball, respectively. The lateral and medial of these arteries follow a long intrabulbar trajectory after having supplied several short posterior ciliary arteries to the choroid. The anterior ciliary arteries consist of a dorsal and a ventral vessel which penetrate the eyeball in the pericorneal area. The choroidoretinal arteries form an arterial network around the optic nerve at the posterior pole of the eyeball. They give rise to all retinal arterioles and some peridiscal choroidal branches. The larger part of the choroid is supplied by branches of the posterior ciliary arteries. Additionally, the anterior choroid receives recurrent branches from an arterial circle that lies externally in the ciliary ring. The iris contains a major arterial circle formed by the lateral and medial long posterior ciliary arteries and both anterior ciliary arteries. A minor iridic arterial circle nor central retinal artery could be found in the equine eyes examined.

The distribution of intratubular dentine in equine incisors: a scanning electron microscopic study.

The distribution of intratubular (peritubular) dentine was studied by scanning electron microscopy in 12 equine incisor teeth. High levels of intratubular dentine were found in the peripheral regions of the dentine. In these areas, a marked asymmetry occurred, as intratubular dentine was predominantly deposited onto the side of the dentinal tubular walls nearest to the dentino-enamel junction. The quantity and asymmetry of intratubular dentine were reduced towards the centre of the tooth. The significance of these variations in the amount and distribution of intratubular dentine between the different dentinal regions is discussed.

A study of the ultrastructure and staining characteristics of the 'dental star' of equine incisors.

The objective of this study was to examine the diameter, extent, orientation and contents of dentinal tubules in order to validate the hypothesis of pigment penetration into the dental star of equine incisival occlusal surfaces. The time of appearance and the configuration of the dental star on the incisival occlusal surface are macroscopically visible features that, along with other more reliable parameters, are used for the determination of horses' age. Although dental stars are an integral part of the equine incisor occlusive surface, the exact nature and microstructure of the dental star are poorly documented. Therefore, equine incisor dentine was examined macroscopically and by scanning electron microscopy to elucidate numerical density, diameter and 3-dimensional organisation of the dentinal tubules in the dental star. The dental star is surrounded by primary dentine and consists of a central core of tertiary dentine, an intermediate ring of pale secondary dentine and a peripheral rim of darker, yellowish-brown secondary dentine. The central core of tertiary dentine contains relatively few dentinal tubules (<8000/mm2) that have small diameters (mean +/- s.d. 1.67 +/- 034 microm) and are arranged in an irregular pattern. The surrounding pale ring of secondary dentine comprises manifestly more and wider tubules that lie almost parallel to the occlusal surface. The dark peripheral rim of the dental star contains high numbers of tubules (28,000-58,000/mm2) that have wide luminal diameters (mean +/- s.d. 3.09 +/- 0.31 microm) and open perpendicular to the occlusal surface. In contrast, the primary dentine surrounding the dental star is made up by a lower number of dentinal tubules (<25,000/mm2). The tubules of primary dentine, which are initially mean +/- s.d. 5.15 +/- 0.80 microm wide, are narrowed by circumferential deposits of peritubular dentine and are obliquely exposed at the occlusal surface. From these observations, it was concluded that the regional differences in numerical density, diameter and spatial orientation of the dentinal tubules may influence the penetration of food pigments into the equine occlusal surface and result in the particular staining of the dental star.

The effect of parenteral use of estradiol, progesterone, testosterone and trenbolone on growth and carcass composition in pigs.

One hundred sixty-two Belgian Landrace pigs were fed ad libitum from 20 to 100 kg in individual pens (Exp. 1 and 2) or in group pens (Exp. 3). Boars were implanted in the range of 54 to 61 kg live weight with either estradiol-17 beta + progesterone (Exp. 1) or estradiol-17 beta + trenbolone (Exp. 2 and 3); barrows were treated in the same weight interval with either estradiol-17 beta + trenbolone (Exp. 1) or estradiol-17 beta + testosterone (Exp. 2); gilts received either estradiol-17 beta + testosterone at 60 kg (Exp. 1) or estradiol-17 beta + trenbolone at 57 kg (Exp. 2) and at 51 kg (Exp. 3). Growth performances and carcass characteristics were recorded. Carcass composition was evaluated by chemical analysis of the carcass (Exp. 1) or of the loin (Exp. 2). Regardless of sex of the pig, all hormone treatments adversely affected growth rate of the pigs, except that of gilts of Exp. 1 which had an improved rate of growth (P less than .05). There was a concomitant reduction of the voluntary feed intake in the cases of growth depression. The feed:gain ratio in this period was only improved (P less than .01) in the barrows of Exp. 1. The most striking feature concerned the carcass composition, which became leaner in all treated animals except for the boars in Exp. 1, where the carcass composition was unaffected by treatment.

Comparative morphology of the pectinate ligaments of domestic mammals, as observed under the dissecting microscope and the scanning electron microscope.

The pectinate ligaments of ten horses, two donkeys, five oxen, five sheep, ten goats, five dogs, five cats, thirty pigs and two rabbits were studied under the stereomicroscope and the scanning electron microscope. In the horse and the donkey, the pectinate ligament was very prominent and was characterized by sturdy interconnected strands and relatively small intertrabecular spaces. The pectinate ligaments of ruminants were composed of shorter strands, separated by relatively larger spaces. Fusion between adjacent strands, resulting in the formation of fenestrated sheets, was regularly observed in these species, in particular in the superior and inferior ocular segments. In the dog and the cat, the pectinate ligament consisted of slender strands that were separated by large intertrabecular spaces. The strands of the pectinate ligaments of the pig and the rabbit were shorter and their diameters were intermediate between those of the herbivores and the carnivores. The clinical relevance of the normal variability in the structure of the pectinate ligament and proposals for a uniform anatomical nomenclature are discussed.

Morphometric analysis of the foramen magnum in Pekingese dogs.

The size and shape of the foramen magnum were studied in skulls from 75 adult and 5 juvenile Pekingese dogs. After maceration of the skulls, the height, width, and area of each foramen magnum were measured, and various skull indices were determined. The shape of the foramen varied from ovoid to rectangular and had a dorsal notch in all but 2 skulls. Prolapse of cerebellum or brain stem through the enlarged opening was prevented by a fibrous membrane covering the dorsal notch. Mean +/- SD area of the foramen was 138.1 +/- 26.1 mm2; its mean total height was 15.0 +/- 2.9 mm, and its mean maximal width was 13.3 +/- 1.1 mm. Statistically, variability in the area of the foramen was mainly correlated with total height of the foramen, including the dorsal notch. Total height of the foramen was not correlated with age or gender. The degree of dysplasia, notch index, and occipital index of each foramen magnum were determined. To allow a more accurate evaluation of the morphology of the foramen, the foramen magnum index, defined as the ratio between the maximal width and the total height of the foramen, was also computed. Mean +/- SD foramen magnum index was 91.8 +/- 17.1 in the adult Pekingese dogs. Foramen magnum index was not significantly correlated with age, but was significantly larger in male than in female dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Ageing horses by an examination of their incisor teeth: an (im)possible task?

It is generally considered that the age of a horse can be determined by examining its incisor teeth. However, the criteria used to determine age from dental configurations differ widely. The existence of this variety of rules and guidelines was the challenge for the present examination. Detailed descriptions of the incisor teeth of 212 horses of registered age were recorded and the results were compared with the age criteria of various authors. The time at which teeth were shed and the appearance of dental stars seemed to be more reliable features than the disappearance of the cups. The disappearance of the marks occurred four years later than usually stated. Other criteria, such as the presence of the seven-year notch and Galvayne's groove, were too variable and inconsistent to be reliable for the determination of age.

Comparative efficacy of closantel and triclabendazole against Fasciola hepatica in experimentally infected sheep.

The effect of closantel (10 mg/kg orally) and triclabendazole (10 mg/kg orally) on the reappearance of a patent infection of Fasciola hepatica was studied in experimentally infected sheep. The treatments resulted in the interruption of faecal egg output for 11 weeks with triclabendazole and 13 weeks with closantel. Necropsy of untreated control animals revealed a mean burden of 360 flukes with a mean (+/- se) surface area of 171 +/- 64.3 mm2, whereas the fluke burdens in the closantel and triclabendazole-treated animals 14 weeks after treatment were 61 (83 per cent reduction) and 21 (94 per cent reduction), respectively. The surface areas of the flukes in the triclabendazole-group were comparable with the untreated controls (141 +/- 51.8 mm2), but the flukes in the closantel group were markedly smaller (43.1 +/- 26.9 mm2). It is concluded that closantel has, in epidemiological terms, a potency comparable with that of triclabendazole, despite its slightly lower efficacy against the very immature stages.

Preferential sites for arterial blood sampling in cattle.

The aim of this study was to compare the feasibility and reliability of different methods for obtaining samples of arterial blood from calves and adult dairy cows. The intermediate branch of the caudal auricular artery was easy to use in animals of all ages. The common carotid artery was also suitable, but only in standing animals. In recumbent animals, the brachial artery and the common palmar digital artery were suitable in calves up to six months old, and the saphenous artery was suitable in both young and adult cattle. The facial, axillary and median caudal arteries were either difficult to use or unreliable.

Histological study of the innervation of the suspensory ligament of the forelimb of the horse.

The innervation pattern of the interosseus muscle of the forelimb was studied in two ponies and two horses. The nerves of the suspensory ligament were studied histologically after neurectomy of the ulnar and median nerve branches proximal to the carpal joint. The results demonstrated that the interosseus muscle is innervated by the deep branch of the lateral palmar nerve which emerges at the level of the midcarpal region and contains fibres from the ulnar and the median nerve. These findings provide evidence that an ulnar nerve block proximal to the accessory bone would fail to anaesthetise the entire suspensory ligament.

Ageing Arab horses by their dentition.

The dentition of 170 Arab horses of known ages was examined and compared with the dental characteristics of trotter horses and Belgian draft horses of the same ages. The results indicated that inaccuracies in the determination of the age of horses by their dentition may result, at least partly, from differences between the breeds of horse involved because there were some major differences between the three breeds examined. These differences increased as the horses' true age increased. In general, the rate of dental wear was slower in the Arab horses than in trotter horses and Belgian draft horses.

Ageing draft and trotter horses by their dentition.

The accuracy of ageing horses by their dentition was assessed by comparing the dental features with the known dates of birth of 212 trotter horses and 189 Belgian draft horses. The horses ranged in age from two to 25 years. In both breeds it was observed that the shedding of the incisors and the appearance of the dental stars were the most reliable features for age determination. In young animals, the dental configuration was similar in both breeds. With increasing age the incisor teeth of draft horses were more liable to abrasion than those of trotter horses. The sequential changes in appearance of the permanent incisors occurred earlier in draft horses than in trotters.

Dental wear in horses in relation to the microhardness of enamel and dentine.

The microhardness of enamel, primary dentine and secondary dentine was determined in the incisor teeth of 39 horses of three different breeds, trotter horses, Belgian draft horses and Arab horses. Using a microhardness tester fitted with a Knoop diamond indenter, the overall Knoop Hardness Number was determined for each tissue, and the influence of breed and age on the hardness were evaluated. Enamel and secondary dentine were significantly harder in Arab horses than in trotters and Belgian draft horses, but there were no significant differences between draft horses and trotter horses in the hardness of their enamel and dentine.

Anaesthesia for fluorescein angiography of the ocular fundus in the miniature pig.

A safe and reproducible procedure is described for anaesthesia and ophthalmic fluorescein angiography in the miniature pig. Twenty examinations were performed in five adult miniature pigs. A detailed description is given of the anaesthetic procedure, in particular of the techniques for endotracheal intubation and for intra-arterial and intravenous cannulation. All cardiovascular parameters recorded during the experiments remained within acceptable anaesthetic limits. The fluorescein angiographic technique, which is routinely used in human ophthalmology, was adapted for the pig. This procedure for in vivo examination of the porcine eye is interesting and useful for experimental ophthalmic research.