Biomedical subjects
Publications and source records attributed to S R van Amstel.
The thickness of the subsolar soft tissue layer (dermis and subcutaneous tissue) of the hind lateral and medial claws of 23 Holstein dairy cattle was measured by ultrasound imaging. The results showed that on average the subsolar soft tissue layer of the lateral hind claw was significantly thicker (4.29 mm) than that of the medial hind claw (3.92 mm).
Thin soles and resulting lameness are often associated with increased culling rates in large dairy operations. The moisture content of the sole horn may cause the horn to be softer, thus predisposing it to an increased rate of wear. For that reason, the first objective of this study was to determine the moisture content of the sole horn of thin-soled cows. The second objective was to document physical changes of the claw associated with thin soles. Twenty-six adult Holstein cows showing signs of thin soles, and 16 normal cows were used in the study. Selection criteria for thin-soled cows included a dorsal wall length of less than 7.5 cm and the following clinical signs: painful gait, arched back, and specific leg lameness. Sixteen normal adult cows with dorsal wall length in excess of 7.5 cm were randomly selected. For thin-soled cows, the moisture contents of sole horn were 37.1 +/- 0.7% for front claws and 40.5 +/- 0.7% for rear claws. These values were significantly different from each other. Moisture contents of sole horn from normal cows were 31.08 +/- 0.93% for front claws and 33.1 +/- 0.9% for rear claws, which were significantly different from each other and different from thin-soled cows. Rear claws had higher moisture contents than front claws. Mean sole horn thickness was 4.23 +/- 0.18 mm for the rear lateral claws and 5.15 +/- 0.18 mm for the rear medial claws. The average dorsal wall lengths were 66.8 +/- 3.94 mm for rear lateral claws and 69.1 +/- 7.25 mm for rear medial claws. Thirty percent of rear feet with thin soles had pathological claw horn lesions including sole/white line separation (72%) and sole ulcers (28%). Of the affected claws, 13% had more than one lesion. Seventy-seven percent of claw lesions occurred in the lateral claw.
In 1997, Wilmut et al. announced the birth of Dolly, the first ever clone of an adult animal. To date, adult sheep, goats, cattle, mice, pigs, cats and rabbits have been cloned using somatic cell nuclear transfer. The ultimate challenge of cloning procedures is to reprogram the somatic cell nucleus for development of the early embryo. The cell type of choice for reprogramming the somatic nucleus is an enucleated oocyte. Given that somatic cells are easily obtained from adult animals, cultured in the laboratory and then genetically modified, cloning procedures are ideal for introducing specific genetic modifications in farm animals. Genetic modification of farm animals provides a means of studying genes involved in a variety of biological systems and disease processes. Moreover, genetically modified farm animals have created a new form of 'pharming' whereby farm animals serve as bioreactors for production of pharmaceuticals or organ donors. A major limitation of cloning procedures is the extreme inefficiency for producing live offspring. Dolly was the only live offspring produced after 277 attempts. Similar inefficiencies for cloning adult animals of other species have been described by others. Many factors related to cloning procedures and culture environment contribute to the death of clones, both in the embryonic and fetal periods as well as during neonatal life. Extreme inefficiencies of this magnitude, along with the fact that death of the surrogate may occur, continue to raise great concerns with cloning humans.
Foot care and claw trimming require proper systems for restraint, sharp knives and trimming equipment, and an understanding of the biomechanics of weight bearing and hoof overgrowth in cattle. The objective of functional claw trimming is to correct hoof overgrowth, thereby re-establishing appropriate weight bearing within and between the claws of each foot. Traditional trimming methods fail to achieve these objectives. Corrective trimming procedures are applied to horn lesions affecting the claw capsule. Primary objectives of corrective trimming are to adjust weight bearing to provide rest for diseased claws and to remove loose horn and hard ridges that may cause further injury to the corium. The application of a foot block to the healthy claw is a valuable aid in foot care when corrective trimming alone is insufficient to provide needed relief from weight bearing. Finally, the use of topical treatments under a bandage is controversial. It is recommended that caustic treatments be avoided and that the use of a bandage be limited to conditions requiring hemostasis or when operators are committed to their removal within a period of 2 to 5 days depending on the level of environmental contamination.
The normal development of the horn capsule (epidermis), with its dermal support (corium), is described. Abnormalities of horn growth may be caused by changes in blood flow (laminitis), the biomechanics of weight bearing, heritable developmental conditions, and other changes of unknown cause.
Diuretics, in particular furosemide, are generally recommended as a supportive treatment in the advanced stages of heartwater in ruminants. However, after what appeared to be possible adverse effects accompanying its use in field cases of heartwater, the effects of this drug on certain blood and urine parameters were investigated in normal sheep at the same dose rates. Diuresis with concomitant natriuresis was significant after furosemide administration, as was the expected plasma volume decrease. Other significant changes included metabolic alkalosis, hypokalaemia and reduced blood ionised calcium. The difference in duration of the diuretic effect and the duration of the changes in blood parameters from c. 3 h and c. 6 h respectively make it difficult to determine a time interval between successive treatments with furosemide. It appears that the probable cause of death of sheep with heartwater is a drastic reduction in blood volume and decreased cardiac output that leads to general circulatory failure. A therapeutic approach that involves further loss of plasma volume due to diuresis appears contradictory. The added effects of potentiating respiratory alkalosis and the terminal drop in blood ionised calcium seen in heartwater-affected animals indicate that the use of furosemide in supportive treatment of this disease is not warranted.
An outbreak of digital dermatitis in a dairy herd in the Gauteng province of South Africa is described in which 72% of the lactating herd was affected. Many of the affected cows showed a severe lameness and a drop in milk production. Other complications included heel horn erosion, under-running of heel horn and boxy claws. The diagnosis was made on the typical clinical appearance of the condition and the presence of spirochaetes on histopathological sections from biopsy material. The condition responded to spraying affected feet with an oxytetracycline mixture after cleaning with water using a high pressure hose. The prevalence was reduced to 28% after one month of therapy. A repeat outbreak occurred on the same farm 7 months later during which time 37% of the lactating herd was affected. Of the cows affected, 48% represented new cases, whereas the rest were reinfections.
Renal dysplasia is reported in two adult horses in chronic renal failure. Renal dysplasia, complicated by severe interstitial pyelonephritis, was diagnosed on renal biopsy and confirmed on post mortem examination.
Three cases of horses with nutritional secondary hyperparathyroidism (NSH) are described. The horses showed typical thickening of the maxillae and mandibular bones with or without lameness. Laboratory findings included elevated concentrations of parathyroid hormone (carboxy-terminal and mid-molecule fractions), alkaline phosphatase and an increase in the fractional excretion rate of serum inorganic phosphorus.
The results of a study conducted to determine the clinical changes in 4 experimentally-induced cases of endotoxaemia in the horse are reported on. Endotoxaemia was induced by injecting commercially available E. coli 055:B5 lipopolysaccharide intravenously at a dose of 1 microgram kg-1. The parameters that were monitored include general behaviour, rectal temperature, heart rate, respiratory rate and quality, pulse quality, mucous membrane colour, capillary refill time, appearance of the faeces and the presence of laminitis. Increases in rectal temperature, respiratory and heart rate, capillary refill time, the development of a bounding peripheral pulse, dyspnoea and congestion of mucous membranes, decrease in faecal consistency and behavioural changes were recorded.
The results of a study conducted to determine the clinico-pathological changes in 4 experimentally-induced cases of endotoxaemia in the horse are reported on. Endotoxaemia was induced by injecting commercially available E. coli 055:B5 lipopolysaccharide intravenously at a dose of 1 microgram kg-1. The haematocrit, red cell count, total and differential white cell counts, thrombocyte count, prothrombin time, partial thromboplastin time, fibrinogen level, level of fibrin degradation products, arterial acid-base status, serum lactate and blood glucose were determined repeatedly. Changes that occurred, include increases in the haematocrit and red cell count, a leucopaenia followed by a leucocytosis caused mainly by changes in the number of neutrophils, the development of disseminated intravascular coagulation, minor changes in the arterial acid base parameters, hyperglycaemia followed by hypoglycaemia and an increase in serum lactate.
Studies to evaluate cardiac and pulmonary function were undertaken in 4 calves suffering from experimentally-induced heartwater. There was a marked variation in the course of the disease. Three of the calves recovered spontaneously after developing clinical signs. These included a rectal temperature in excess of 40 degrees C, anorexia and listlessness but no neurological signs. The remaining calf died 2 days after developing a fever and neurological signs. In the 3 calves that recovered, a mild hypoxemia developed during the acute stage of the disease. Arterial CO2 tension remained within normal limits, but there was a tendency towards an alkalosis. Increases in pulmonary dead space and fluctuations in venous admixture were observed. The calf that died showed similar mild changes in blood gas parameters, despite the presence of a marked reduction in minute volume, and a lung oedema was demonstrated on post-mortem examination. No marked changes in systolic and diastolic blood pressures and in right cardiac intraventricular pressures were observed. Terminally, however, there were marked decreases in stroke volume and cardiac output. These changes were associated with a sharp increase in heart rate. No primary cardiac pathology was observed on clinical and post-mortem examinations.
The presence of endotoxin was examined in 5 sheep with experimentally-induced heartwater. Two peaks in endotoxin levels were recorded in 4 out of the 5 sheep during the acute stage of the disease. The 1st peak coincided with or occurred shortly after the febrile reaction (over 40 degrees C). The 2nd peak occurred 3-5 days after the 1st, and in 2 sheep this 2nd elevation in endotoxin levels was associated with severe clinical signs (rapid and laboured breathing, cyanosis and recumbency), and 1 of the 2 sheep died on the day of the 2nd elevation. Both endotoxin peaks were of short duration and levels had decreased in the 24-h follow-up samples.
Experimentally-induced cases of sweating sickness in calves were used in an effort to correlate the blood chemistry with some of the known pathological changes. Results showed that the "sweating" associated with necrotic dermatitis did not alter blood electrolyte levels. Laboratory evidence of a disseminated intravascular coagulopathy was found which correlated with the microthrombi described in cases of sweating sickness. A high blood cortisol level was found in one of the animals that died from the disease and could possibly be used as a prognostic indicator in clinical cases. Recommendations are made with regard to the supportive treatment based on the clinical pathological findings.
Bacterial isolations from tracheal and bronchial washes obtained with the aid of a fibreoptic endoscope were carried out over a 7 month period in a feedlot on calves suffering from acute pneumonic pasteurellosis. Pasteurella haemolytica and Pseudomonas aeruginosa represented the majority of isolates. Antibiotic sensitivities of the Pasteurella isolates are reported on.
Variable results were obtained when the starch digestion test was carried out on a suspected case of malassimilation in a horse. In order to re-evaluate this test, 15 starch digestion tests were carried out using 4 horses. Results showed a marked variation in the increase in plasma glucose levels between individual horses and especially between poor and good condition horses when the dose of starch was based on body mass. Results also suggest that a fixed dose of starch may give more consistent results.
A nematode of the genus Anatrichosoma caused extensive necrosis and sloughing of the footpads of a domestic cat. No male worms were found but a description of the female is given. This is the first report of Anatrichosoma sp. in the Republic of S.A. as well as the first report of it in a cat.