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Biomedical subjects

E C Webb

Publications and source records attributed to E C Webb.

At least 19 recordsLinked to original sources

Electrocardiographic surrogates of structural myocardial alterations in the Dorper sheep heart.

In this study we evaluated the validity of well-known human electrocardiographic markers of myocardial pathology in Dorper sheep. These markers include: the duration of the QRS complex of premature ventricular complexes (PVCs), the presence of notching of the QRS complex of PVCs and change of the ST-segment of PVCs. It was shown that these three electrocardiographic phenomena correlate with myocardial pathology in the hearts of Dorper sheep. We also describe a new electrocardiographic indicator of myocardial pathology, namely an increase in the frequency of cardiac memory T waves as a new electrocardiographic surrogate for myocardial pathology in the hearts of Dorper sheep.

Animals↗

An economic analysis of communal goat production.

The economic impact of different extension messages used was calculated using enterprise budgeting (gross margin analysis). Input data were gleaned from the literature, from participatory appraisals, as well as a field study, spanning 12 months, of small-scale communal goat farming systems in Jericho in the Odi District of North West Province. The number of offspring weaned per annum, as a proportion of does owned, was selected as the desired output for analysis. This study has shown that small-scale communal goat farmers are not adopting or implementing extension messages to improve production capacity. In South Africa the majority of goats are slaughtered in the informal sector. If the informal sector is to be persuaded to market goats commercially through formal channels, then knowledge of the economics of goat farming on communal lands should be provided. The economic aspects of extension messages are probably an important factor in determining acceptance and sustainability yet appear to be seldom investigated. The probable reason for lack of adoption of standard extension messages, which promote improved nutrition, parasite control, vaccination and treatment of goats, was economic. In other words, the so-called 'poor management practices' used by communal farmers appeared to be economically more profitable than the 'good management practices' suggested to increase production. The price of communal goats was not related to their mass. A higher level of inputs would probably have resulted in a heavier kid, however it was established that this would not have influenced the price received as a majority of the goats were slaughtered for ritual purposes where age, colour and sex were more important to the purchaser than body mass. It is standard practice in commercial farming systems to evaluate the economic benefits of all management practices before they are implemented. Production animal veterinarians use veterinary economics to compare different scenarios to control diseases or select management practices in commercial herds. It is suggested that the inputs and outputs of small-scale farming systems should be carefully analysed and that veterinary economics should also be used to evaluate the probable impact of extension messages formulated by veterinarians and animal health technicians.

Animal Husbandry↗

Ventricular dyssynchrony as a cause of structural disease in the heart of Dorper sheep.

Ventricular dyssynchrony is a disturbance of the normal, organized electromechanical coupling of the two ventricles. This condition has many causes, such as left bundle branch block, ventricular preexcitation, right ventricular pacing and right ventricular premature ventricular complexes (PVCs). Ventricular dyssynchrony has many adverse haemodynamic effects on the left ventricle and we wanted to know whether these adverse haemodynamic effects might have any structural consequences on the left ventricles of such hearts. Six healthy Dorper wethers were subjected to numerous right ventricular PVCs to induce ventricular dyssynchrony in order to determine whether any structural consequences will occur in the left ventricles of these hearts. Myocarditis in the musculature of the left ventricles of all six these hearts was seen.

Animals↗

The heart remembers: observations of cardiac memory in the Dorper sheep heart.

Memory is a property common to a diverse range of tissues. Cardiac memory has been demonstrated in the human, dog, rat and rabbit. This is a peculiar phenomenon, reflected in the T wave of the electrocardiogram. The heart is able to remember periods of alterations in the sequence of ventricular activation and once there is a return to a normal sequence of ventricular activation the T waves may manifest memory. Cardiac memory is noted when the T wave during normal ventricular activation retains the vector of the previous abnormal QRS complex, caused by a period of altered ventricular activation. Possible mechanisms of memory in the heart are alterations of the transient outward potassium current (I10) in ventricular myocytes and new protein synthesis inside myocytes. These two mechanisms operate in short- and long-term cardiac memory respectively. Currently, it is unknown whether memory may have adverse structural consequences in the heart. We were able to demonstrate memory in the hearts of Dorper wethers and this is the first report of cardiac memory in Dorper sheep.

Animals↗

Ventriculo-atrial conduction in the ovine heart, caused by premature ventricular complexes.

In humans, and certain animals, the atrioventricular conduction system is capable of bidirectional conduction. Depolarization impulses, originating in the ventricle itself, may thus be conducted in a retrograde direction towards the atria. Two common causes for this phenomenon of ventriculo-atrial (retrograde) conduction are premature ventricular complexes and ventricular pacing. The surface electrocardiogram can be used for the detection of such retrogradely conducted beats. The purpose of this study was to investigate the possibility of ventriculo-atrial conduction in Dorper sheep. Premature ventricular complexes in eight healthy Dorper wethers were induced and it was possible to document retrogradely conducted beats on the surface electrocardiogram in all of them. It is concluded that the Dorper sheep heart is capable of ventriculo-atrial conduction.

Animals↗

Copper, manganese, cobalt and selenium concentrations in liver samples from African buffalo (Syncerus caffer) in the Kruger National Park.

Animals may act as bio-indicators for the pollution of soil, air and water. In order to monitor changes over time, a baseline status should be established for a particular species in a particular area. The concentration of minerals in soil is a poor indicator of mineral uptake by plants and thus their availability to animals. The chemical composition of body tissue, particularly the liver, is a better reflection of the dietary status of domestic and wild animals. Normal values for copper, manganese and cobalt in the liver have been established for cattle but not for African buffalo. As part of the bovine tuberculosis (BTB) monitoring programme in the Kruger National Park (KNP) in South Africa, 660 buffalo were culled. Livers (n = 311) were randomly sampled in buffered formalin for mineral analysis. The highest concentrations of copper were measured in the northern and central parts of the KNP, which is downwind of mining and refining activities. Manganese, cobalt and selenium levels in liver samples indicated neither excess nor deficiency; however, there were some significant area, age and gender differences. The results will be useful as a baseline reference when monitoring variations in the level and extent of mineral pollution on natural pastures close to mines and refineries.

Animals↗