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    The role of dietary calcium in the control of egg production : a thesis ... for the degree of Master of Agricultural Science at Massey University
    (Massey University, 1975) Gibbins, Alan Michael
    Dietary calcium restriotion is studied as a method of controlling egg production. Attempts have been made to delay the onset of egg production in the fowl by feeding pre-laying diets deficient in calcium. Calcium restriction had no apparent effect on sexual development and did not delay the time· of first oviposition. Low calcium diets were used at a later date to halt egg production firstly just after peak production and secondly towards the end of the first laying year. Egg production was depressed markedly but never completely ceased, and remained at a low level until calcium restrictions were lifted whereupon a rapid rise returned egg production to levels comparable to egg production rates of non calcium restricted control hens. Comparisons between egg production, egg weight, shell weight and a measure of shell quality (shell weight per unit surface area of egg) revealed trends towards improved shell production and shell quality following calcium restriction but little else. There was only a small number of significant differences. Egg production pauses induced by low dietary calcium were thought to be unsatisfactory as substitutes for force moulting. Calcium restriction caused declines in food consumption and body weight. While food consumption returned to levels equivalent to food consumption of non calcium restricted hens after calcium restriction, body weight in general did not. Calculations of the calcium loss from the body of calcium restricted hens via egg·shell production show that extremely severe depletion occurs unless egg prvduction is stopped or at least egg shell production is stopped. Such depletion of calcium has greatest effects on the skeleton and damage to the bones, particularly of the legs, may result. This is a condition which may predispose to a paralytic condition characteristic of extreme calcium deficiency.
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    Some economic and nutritional aspects of different grower and layer rations in egg production : a thesis presented in partial fulfilment of the requirements for the degree Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1970) Swan, Stephen Edgar James
    Preface: Chapter One of this thesis presents background information on the rearing of laying pullets and describes an experiment evaluating a series of rearing rations (with continuous variation of the levels of three major ingredients) in terms of overall profitability. Chapter Two looks particularly at the layer phase, and considers possibilities of reducing feed costs in this phase. An experiment evaluates a series of layer rations (with continuous variation of the levels of three major ingredients) in terms of overall profitability. The final chapter presents an appraisal of the methods available for economic analysis of livestock rations, and discusses the problems associated with their application in layer nutrition. A profit function is suggested as a means of economic evaluation.
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    An economic analysis of least-cost layer rations : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Farm Management at Massey University
    (Massey University, 1974) Ryan, Oliver Patrick
    Fifteen treatments, replicated once, each containing eighty four birds of three strains of White Leghorn layers (White Base a, White Base b, M. Line) were fed rations ad libitum of five different metabolisable energy levels (2315, 2535, 2756, 2976, 3197 k. cal. M.E. per kg.) and three different protein levels (16, 17, 18 gms. per hen per day, based on an energy intake of 305 k. cals. per hen per day) to obtain quantitative estimates of the physical input/output relationships of layer production. Three other treatments, plus a control, were fed to obtain data on the response of laying hens to restricted energy intake and improved protein quality. All rations were formulated to least cost using Linear Programming. Least Squares multiple regression was used to obtain linear response functions for feed intake, egg number, egg weight and liveweight gain (the variables included in a net revenue function for layers under New Zealand production conditions). Feed intake was expressed in terms of dietary energy concentration and initial liveweight. Statistical problems encountered dictated that predicted nutrient intakes were used as the independent variables in the estimation of the egg number and liveweight gain functions. Predicted energy intake and methionine intake accounted for differences in egg number, particularly for White Base b layers. Predicted energy intake, methionine intake and isoleucine intake accounted for differences in liveweight gain. There were no significant differences between average egg weights. There were significant strain differences in ad libitum feed consumption, egg number, average egg weight and liveweight gain. A net revenue function was estimated in terms of the endogenous variables (dietary nutrient concentrations) which were included in the layer response functions. This was analysed in terms of the endogenous variables for the then current egg and feed prices.