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    The effects of method of pre-lamb shearing of ewes on production and physiological indicators of cold stress : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1990) Kamil, Kurnia Asumatrani
    This experiment was undertaken to compare the effects of two methods of pre-lamb shearing on physiological and production characteristics of ewes and their lambs with the objective of determining which method gives the greater advantages. In July, approximately 20-63 days before lambing, sixty Romney ewes were divided at random into two equal groups, one group was shorn with a conventional comb and the other using a cover comb. The former left wool 1-3 mm in length and the latter 6-13 mm of wool on the animal after shearing. The ewes were run together on a rye grass white clover pasture for a 67 day period after shearing. Climatic conditions were considered mild with average minimum temperature of 5.2 °C, and average maximum temperature of 13.4 °C, average wind speeds of 8.5 km/h, relative humidity 80.1 %, sunshine 4.7 h and 1.2 mm of rainfall over the 67 days period after shearing. Food intake, measured indirectly using controlled-release capsules containing chromium sesquioxide placed in the rumen, did not differ between the groups over a 21 day period after shearing. This was reflected in a lack of effect of treatment on the live weight of the ewes, birth weight of the lambs, growth rates of the lambs or wool growth of the ewes over the 67 day period. Ewes shorn by the conventional comb, however, were more severely stressed than the ewes shorn with the cover comb as indicated by the higher concentrations of non-esterified fatty acid (NEFA) and 3-hydroxybutyrate in the plasma of the former group on days 1 and 3 after shearing. Rectal temperature was a less sensitive measure than the concentrations of the metabolites and the difference between the groups in rectal temperature after shearing was not statistically significant. It was concluded that shearing with a cover comb reduces the cold stress on the ewe in comparison with the conventional method of shearing. Furthermore, it was suggested that under more severe climatic conditions than those experienced in the present experiment, that shearing with the cover comb might be expected to result in increased production.
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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.