Biomedical subjects
G F Bath
Publications and source records attributed to G F Bath.
The effect of a natural maedi-visna virus infection on the productivity of South African sheep.
A cohort study was conducted in order to measure the effect of the chronic indurative lymphocytic mastitis caused by the South African strain of maedi visna virus (MVV) on the pre-weaning growth of lambs born either of naturally infected or uninfected ewes kept under similar conditions. Fifty naturally infected ewes as well as another 40 from a maedi-visna-free source to be used as control animals, were purchased and kept in separate flocks which were managed in a similar way. All the ewes were of the same breed and 3-4 years old. During the adaptation period, and through the mating, pregnancy and lactation periods they were periodically monitored for the presence of MVV serum antibodies. The lambs were weighed at birth and thereafter every 2 weeks until the age of 90 days, when they were weaned. The ewes were then slaughtered, and their udders examined histologically and the number of lymphocytic follicles were counted and assessed. Although the calculated values indicated a correlation between the number of follicles in the udder and the reduction in the growth rate of the lambs, this was not statistically significant. Similarly, despite higher counts of lymphoid follicles in the udders of sero-positive ewes as compared to those that were sero-negative and the lower ewe productivity indexes in infected ewes, no statistically significant differences were found in the indexes of ewes in different follicle categories.
Physical structure and chemical composition of abomasal phytobezoars of goats and sheep.
The diameters of fibres from phytobezoars varied between 2 and 30 microns, with an average 58% measuring less than < 15 microns, 36% between 15 and 23 microns, and 6% greater than 23 microns. These diameters were very similar to those of the pappus hairs surrounding the seeds of the Karoo bushes Chrysocoma ciliata, Eriocephalus ericoides and Gnidia polycephala (means of 6.06 microns, 16.67 microns and 22.73 microns respectively). The microscopic structure and ultrastructure of these pappus hairs moreover closely resembled the fibres of bezoars but were quite distinct from that of hair or wool. Of particular interest was the presence of annular thickenings as well as terminal hooks on both bezoar fibres and pappus hairs, both of which structures are believed to be involved in the formation of bezoars. This close similarity between the fibres in bezoars and those of pappus hairs in the 3 plant species studied, leads to the conclusion that the bezoars consisted largely of pappus hairs of these and possibly other species. The chemical composition of bezoars found in goats and sheep, resembled that of pappus hairs and stems of the Karoo bushes Eriocephalus ericoides and Gnidia polycephala more closely than that of mohair. Ash, nitrogen, phosphorus and zinc concentrations in both bezoars and plant material were similar, but very different to that of mohair; however, the calcium, magnesium, potassium and manganese levels of bezoars were more similar to mohair than plant matter. This may have been due to a leaching effect.
Experimental reproduction of phytobezoars.
In a series of in virtro experiments (n = 64) using the mature flowers or seeds and pappus hairs of Karoo bushes Chrysocoma ciliata, Dimorphotheca cuneata, Eriocephalus ericoides, Gazania krebsiana and Gnidia polycephala, small phytobezoars were formed from material of E. ericoides, G. krebsiana and G. polycephala either alone or in combinations. The ratio of fibre to liquid used was found to be optimal around 1: 7 and milling of material enhanced bezoar formation. Time and pH did not appear to significantly affect the formation of bezoars. Other factors were either standardised or not studied. In a small in vivo trial, 4 groups of one sheep and one goat each were fed 10% of either C. ciliata, E. ericoides, G. polycephala seeds and pappus hairs, or a mixture of all 3, added to a basal diet of milled lucerne fed for up to 31 d. Small phytobezoars were formed in the goats but not the sheep receiving C. ciliata, and G. polycephala material. It was concluded that phytobezoars could form in goats or sheep eating large quantities of mature flowers or seeds of several Karoo bushes.
[The threat of wide dissemination of anthelmintic resistance by veld ram performance testing units].
A veld ram performance testing unit consists of an association of stud or commercial ram breeders, who compare the performance of selected rams under field conditions on common pastures. The best performers are subsequently auctioned at public sales. To date, at least 10 Merino veld ram clubs have been established in various centres in South Africa. A strain of Haemonchus contortus, which was isolated from the pastures of one of these performance testing units, was found to be resistant to ivermectin, oxfendazole and rafoxanide. Closantel, levamisole and disophenol were more than 99% effective. The wide dispersal of the rams after testing, constitutes a potential danger for dissemination of helminths with resistant genes. Precautionary methods should include careful routine monitoring of drug susceptibility on the communal pastures, on the farms of individual members and thorough deworming of rams before they leave the testing unit. The prevention and control of resistance in such testing units are discussed, but it is emphasised that this is difficult, particularly if the worm strains on the communal grazing have become resistant to some of the anthelmintic groups.
A field strain of Trichostrongylus colubriformis resistant to levamisole and morantel in South Africa.
A strain of Trichostrongylus colubriformis from Nottingham Road, in Natal, was found to be solidly resistant to levamisole and morantel at the recommended dose levels. Untreated control sheep in fact harboured fewer worms at slaughter than either of the 2 treated groups. In contrast, the benzimidazoles and ivermectin were more than 99.9% effective against this worm strain. The possible implications of escalating resistance to anthelmintics in the gastrointestinal nematodes of sheep are discussed.
Photosensitivity in South Africa. V. A comparative study of the pathology of the ovine hepatogenous photosensitivity diseases, facial eczema and geeldikkop (Tribulosis ovis), with special reference to their pathogenesis.
The subject of this study was the pathological and scanning electron microscopical changes in the biliary systems of sheep suffering from facial eczema or geeldikkop (Tribulosis ovis), or made photosensitive by ligation of the common bile duct. While an obliterative cholangitis is responsible for the retention of phylloerythrin in facial eczema, the occlusion of bile ducts with crystalloid material (microliths) appear to perform a similar function in geeldikkop. The similarities and differences between the 2 diseases are discussed in the light of their pathogenetic mechanisms.
Photosensitivity in South Africa. II. The experimental production of the ovine hepatogenous photosensitivity disease geeldikkop (Tribulosis ovis) by the simultaneous ingestion of Tribulus terrestris plants and cultures of Pithomyces chartarum containing the mycotoxin sporidesmin.
The mycoflora of toxic pastures were surveyed during a number of outbreaks of ovine hepatogenous photosensitivity in South Africa. Pure cultures of several isolates were dosed to sheep, but only those of Pithomyces chartarum and Myrothecium verrucaria proved to be toxic. Photosensitization was induced in sheep by dosing them with cultures of a P. chartarum isolate (GA10) obtained from Tribulus terrestris plants collected during an outbreak of geeldikkop in the Karoo. Thus for the first time a mechanism whereby T. terrestris plants can contribute to the causation of ovine hepatogenous photosensitivity was demonstrated. When cultures of GA10 equivalent to approximately 0,75--4,0 mg/kg sporidesmin were dosed at Onderstepoort Veterinary Research Institute to Highveld and Karoo sheep on a diet of lucerne, facial eczema was produced. Dosing the same cultures at levels equivalent to c. 1,0 mg/kg of sporidesmin in the Karoo resulted in lesions characteristic of both facial eczema and geeldikkop. Typical hepatic lesions of geeldikkop could be elicited by dosing GA10 at levels equivalent to c. 0,25--0,7 mg/kg of sporidesmin to Karoo sheep grazing on predominantly T. terrestris pastures in the Karoo. In the latter experiment geeldikkop was induced in the sheep on T. terrestris pastures, while those receiving identical doses on veld with little T. terrestris developed facial eczema. Geeldikkop, therefore, can be brought about by the ingestion of T. terrestris plants together with toxic cultures of P. chartarum. The plant appears not only to act as a vehicle for ingestion of spores, but also to interact with sporidesmin to induce lesions typical of geeldikkop, whereas sporidesmin alone results in facial eczema. Indications are that it can enhance the ability of sporidesmin to cause photosensitivity or, possibly, vice versa. The histopathological findings of these experiments are described in detail.
Enzootic icterus--a form of chronic copper poisoning.
The findings of a recent investigation into the epizootiology, course, symptomatology, gross pathology, chemical pathology and prevention of Enzootic Icterus are presented and the findings of previous investigations on these and other aspects are reevaluated. Enzootic Icterus and chronic copper poisoning are shown to be identical in all fundamental features. Both diseases are characterised by sudden onset, high mortality, icterus, anaemia, haemoglobinaemia, methaemoglobinaemia, haemoglobinuria and deeply pigmented kidneys. There are no described microscopic features on which the diseases can be differentiated. Very high levels of copper in the blood, liver and kidneys are found in both diseases. In the present work 36 liver specimens had a mean copper concentration of 701 microgram/g. Of 31 kidney specimens no values under 10 microgram/g were found while the mean was 107 microgram/g. Prevention of Enzootic Icterus by salts of molybdenum given orally confirms the identity. No close relationship with Geeldikkop is found other than the probability that the two diseases may act synergistically. Interpretation of existing knowledge of mineral levels of natural grazing in the enzootic region shows that the levels can account for the presence of chronic copper poisoning, although more investigation is required.
A specific form of abomasal phytobezoar in goats and sheep.
A specific form of phytobezoar in goats and sheep is described with regard to epizootology, symptomatology, gross pathology, and gross morphology of the bezoars. The probable mode of formation and control measures are also discussed.
Cretinism in Angora goats.
An outbreak of goitre and hypothyroidism in newborn Angora kids is described. the does had been grazing on lucerne from the time of mating and received a free-choice lick, which included iodine. Investigations revealed that the condition was iodine-responsive, and was probably caused by a goitrogen like thiocyanate.
Abomasal phytobezoariasis of goats and sheep.
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Geeldikkop: preservation of toxic material.
Wilted Tribulus terrestris plants were harvested from a camp in which geeldikkop had just previously broken out. The plants were treated in various ways in an attempt to preserve their toxicity. The only successful method of preservation found was rapid freezing of harvested material. Three kg of plants were kept frozen for six weeks and then dosed via rumen fistula to a sheep which subsequently developed characteristic symptoms and lesions of geeldikkop.
Congenital diaphragmatic hiatus in a dog.
The symptoms and post mortem findings of a case of diaphragmatic hiatus in a dog are described. At necropsy the caudate and right lateral lobes of the liver, the pyloric portion of the stomach, most of the small intestine and large intestines, the spleen, pancreas and omentum were found in the thoracic cavity.