Factors determining the fertilising ability of avian germ plasm

This thesis reports the results of an investigation into the factors affecting the fertilising ability of avian germ plasm. The study was limited to males of a Rhode Island Red control population and females of a commercial white egg-laying hybrid. The stock was replaced annually from the same source.The investigation was broadly organised according to three major objectives:1) Development of an objective in vitro test to predict fertilising ability.2) A study of some management and biological factors affecting fertilising ability of semen.3) Development of a diluent and conditions for extended storage of fowl semen at high temperatures of 20 and 40°C.A simple, objective, controlled colourimetric technique was developed for estimating the capacity of fowl spermatozoa to reduce a tetrazolium dye to a coloured compound, formazan, which could be measured spectrophotometrically. The reduction of this dye is dependent on number of spermatozoa, incubation temperature and time of incubation. The test is shown to give a quantitative measurement of the metabolic activity of spermatozoa, as judged by their rate of oxygen utilisation, and thus of the quality of semen. The rate of tetrazolium dye reduction was shown to be highly correlated with sperm motility, morphology, ATP content and fertilising ability. The method has many practical advantages over existing tests for the prediction of fertilising ability.A study of frequency of semen collection, over a period of 4 weeks, showed that the fertilising ability was not significantly different when semen was collected twice a day, once a day or thrice a week. Exchange of seminal plasma between samples of semen from males designated as highly or poorly fertile, or as young or old, did not influence the de novo fertilising ability of the original spermatozoal samples.The investigation of the age of male and female revealed that age of male influenced fertilising ability but not the age of females. However, interaction in fertilising ability between age of male and age of female was significant.A simple diluent and storage condition was developed for holding fowl semen at high temperatures of 20° and 40°C for 17 hr. A simple method for storing semen for 6 hr in a still condition on a bench top around 20°C, which should be suitable for field situations, is described.This thesis examines some features of fowl semen physiology concerned with identifying quality of spermatozoa, and some beneficial procedures for the better exploitation of artificial insemination of probable benefit to breeders of commercial poultry