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Subject: search.filters.subject.Sheep anatomy

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    A study of changes in the thickness and chemical composition of the skin of sheep during growth and after shearing : being a thesis presented in partial fulfillment of the requirements for the degree of M. Agr. Sc., Massey Agricultural College, University of New Zealand
    (Massey University, 1954) Wodzicka, Maria Manika
    This study reports on the development of a stochastic dynamic model to simulate a pastoral sheep enterprise. The event driven model was constructed using the iconic simulation package, ExtendTM. Events corresponded to the shifting of animals from one paddock to another. Each paddock was represented as a single entity with inherent attributes such as grazing area, sward characteristics and pasture production potential. The rotation sequence for grazing was determined by always allocating the flock of ewes, flock replacements or lambs to the paddock with the greatest pasture mass. Herbage mass was divided into three fractions: leaf, stem and dead. Pasture growth and senescence rates for individual paddocks were calculated from pasture leaf mass. A Micherlich-type function was used to relate leaf mass to total pasture growth. Senescence was assumed to increase linearly with herbage mass. Deterministic or stochastic pasture growth rate data can be generated by the model. Pasture responses to nitrogen were estimated dynamically and moderated for the farm by entering a user-defined response for a standard 50 kg/ha nitrogen application. Animal performance was calculated using average attributes for ewes, ewe hoggets and rams, but lambs were simulated individually. Lamb performance is affected by its date of birth and sex, and this information was generated by a sub-model for mixed-age ewe and ewe hogget reproduction. The potential herbage intake of the sheep was defined by their rumen fill and physiological energy demand, and herbage availability which was defined by pre-grazing green herbage mass and green herbage allowance for rotational grazing and leaf mass for continuous grazing. The grazing time spent in each paddock was derived from a linear interpolation of user-defined herbage allowances for each month of the year. The proportion of leaf, stem and dead material in the diet was calculated according to the proportion of these fractions in the sward and herbage availability. If animals were supplemented they consumed all of the material offered. This caused pasture substitution by decreasing the physiological energy demand and utilising rumen space otherwise taken up by grazed pasture. The partitioning of nutrients by animals was estimated from the ratio between energy intake and energy demand in an animal growth sub-model. This was driven by the DNA, protein and fat content of individual lambs and the average for animals in other sheep classes. Lambs were drafted for sale and graded according to user-defined threshold drafting weights. Carcass weight and fatness (GR) were generated from the live weight and sex of individuals lambs. A genetic optimisation algorithm was developed to optimise the systems control variables incorporated in the model. These were pasture allowance, supplement fed, nitrogen applied and lamb drafting weight. The model was evaluated against three New Zealand "farmlet" grazing experiments. This validation suggested re-parameterisation of the physiological intake limit is needed and that the British equation used to relate intake to leaf mass availability is overly sensible to the pasture conditions found in New Zealand. The model was also used to test the effects of pasture measurement errors on the profitability of a grazing system. Significant differences in profitability occurred when a CV of 40% in measurement of pasture mass was assumed (Gross margin = $NZ 495 /ha vs. $NZ 542 /ha and $NZ 570 /ha for 20 and 0% CV in measurement estimations and normal variability in pasture accumulation rates and Gross margin = $NZ 587 /ha, $NZ 576/ha and $NZ 519/ha, respectively for 40,20 and 0% CV in measurement estimates and no pasture accumulation rate variability). It was concluded that low gains in system performance can be expected by improving the accuracy of measuring pre-grazing herbage mass beyond the level (13-16% CV) provided by the correct use of current measurement techniques.
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    A study of the shoulder architecture of the sheep involving a comparison between the Romney and Cheviot breed types : being a thesis presented in partial fulfillment of the requirements for the degree of M. Agr. Sc. from the University of New Zealand, 1952
    (Massey University, 1952) Von Borstel, Frank
    In the wild state, the body form of ungulates is determined by two factors:- (1) the animal's necessity to cover ground in search of food and to escape its enemies and (2) its need to convert efficiently the food it obtains into energy for its maintenance and for the performance of the first factor. Another set of environmental responses, those incidental to the perpetuation of the race, appear to have but little influence on the bodily form of the ungulate (Howell, 1944). Hence, in the main, the musculature, skeleton, internal organs and the distribution of fat deposits in such species as the wild cattle or the wild sheep in their evolutionary response to environment would be governed by locomotive demands and the form from which a new adaptation evolved. As pointed out by Simpson (1949):- "in the evolution of a species..... the surviving organisms must meet the minimum requirements of life in an available environment and changes can only occur on the basis of what already exists." This latter factor is sometimes overlooked or not given enough emphasis in animal improvement investigations, but it is all important and probably the main reason why most adaptations are not absolutely perfect and why the selection applied by the domestic animal breeder for meat improvement cannot produce such rapid results as would be hoped.
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    Structural observations on the normal and denervated carotid body and carotid sinus in the sheep (Ovis aries) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Anatomy at Massey University
    (Massey University, 1974) Maung, Sha-Ban
    Structural and ultrastructural observations on the normal and denervated carotid body and carotid sinus of 50 lambs and 7 adult sheep (Ovis aries) were made employing various anatomical, histological, fluorescent, microscopical and ultrastructural techniques. Chronic denervation experiments were performed by (i) unilateral sectioning of the carotid sinus nerve with or without sectioning of the glossopharyngeal nerve and pharyngeal branches of the vagus nerve, and (ii) unilateral sectioning of the sympathetic filament (external carotid nerve) to the carotid trifurcation, or unilateral cranial cervical ganglionectomy. The gross anatomical studies demonstrated that there is variation in the mode of branching of the common carotid artery and the pattern of the venous drainage of the entire carotid region. The position, blood supply and venous drainage of the carotid body were also found to be variable. The major arterial source of supply for almost all the structures associated with the carotid trifurcation is the occipital artery. The dual innervation of the carotid body and the carotid sinus from the glossopharyngeal nerve (via the carotid sinus nerve) and the cranial cervical ganglion (via the external carotid nerve) is described. From the histological studies it was found that there is widespread distribution of carotid body tissue at the carotid trifurcation. Two major cell types were seen in the carotid body, the chief or type I cells and the sustentacular or type II cells. The former included "light" and "dark" cells but it was not possible to identify these cells with certainty under the electron microscope. The carotid body and carotid sinus receive predominantly glossopharyngeal fibres which were traced close to the type I cells in the carotid body, and in the carotid sinus to the deeper tunica adventitia. The large diameter nerve fibres which degenerated after sectioning of the carotid sinus nerve, were seen to terminate in close association with the type I cells. The carotid body cells or the carotid sinus wall did not exhibit any marked morphological changes after sectioning of the carotid sinus nerve or after sympathectomy; however, a marked dilatation of the blood vessels was seen in both the carotid body and carotid sinus. The carotid sinus is a swelling, dilatation or diverticulum at the origin of the occipital artery or the occipitoascending pharyngeal arterial trunk. The extent of the elastic tissue varies according to the position of the carotid body. The carotid sinus is predominantly of the elastic type. The terminal nerve fibres end as diffuse endings. The large diameter myelinated nerve fibres which degenerated after sectioning of the carotid sinus nerve are suggested to be of glossopharyngeal origin, whereas the fine nonmyelinated fibres which could be traced to the medioadventitial border or superficial media are suggested to be of sympathetic origin. Both the normal and sympathetically denervated carotid body cells exhibited intense fluorescence, the intensity of the fluorescence remaining the same up to 8 weeks after sympathectomy. It is suggested that normal carotid body cells contain catecholamines consisting mainly of noradrenaline and dopamine which are not affected by chronic sympathetic denervation. Fluorescent nerve fibres were seen on the outermost layer of the adventitia of the normal carotid sinus, along the carotid body artery, and in the adventitia and the medio-adventitial border of the common carotid and external carotid arteries. They were not present in the denervated specimens. It is suggested that the carotid sinus, carotid body artery and the common carotid and external carotid arteries receive sympathetic adrenergic innervation. Ultrastructuaral studies confirmed the presence of type I and type II cells in the carotid body. The predominant type I cells are characterized by the presence of numerous dark-cored osmiophilic vesicles and mitochondria. The type II cells are irregular shaped cells with a characteristic nucleus, extensive cytoplasmic processes, fewer mitochondria and indistinct endoplasmic reticulum. Blood vessels are numerous in the carotid body. The nerve endings are of two types - large and small, the former being particularly associated with type I cells. Sometimes fine nonmyelinated small axons were seen in the small grooves of the type I cells. Most of the large diameter myelinated nerve fibres and the large type of nerve endings degenerated after sectioning of the carotid sinus nerve. The degeneration was almost complete at 2-8 weeks after nerve transection. After sympathectomy small diameter nonmyelinated nerve fibres which were usually related to the blood vessels, degenerated. It is suggested that the large diameter myelinated nerve fibres and large nerve endings belong to the glossopharyngeal system, and the small diameter nonmyelinated nerve fibres, which are usually related to the blood vessels, are from the sympathetic system. The ovine carotid sinus presented a very similar fibre architecture to that found in the laboratory animals, and the endothelial cells possessed complex endothelial folds. Those nerve terminals which possessed indistinct perineural sheaths and few electron dense-cored vesicles degenerated after sectioning of the carotid sinus nerve, and these nerve terminals are suggested to be derived from the glossopharyngeal nerve. As the nonmyelinated sheathed nerve terminals at the medioadventitial border of the carotid sinus degenerated after sectioning of the external carotid nerve or cranial cervical ganglionectomy, they are suggested to be from the sympathetic system.