Onset of the breeding season in the Corriedale ewe

Any sheep husbandry programme aiming at an improvement of lamb production must rely on known information about ewe and ram reproductive physiology. Of primary importance in the case of the ewe is a knowledge of the breeding season and in particular its onset, since, as this has been demonstrated to vary between breeds and regions, it must be determined for each particular case. The Corriedale breed is known to have its onset earlier than Romneys and later than Merinos and because of its dual purpose nature is particularly suitable for early lamb production, besides that, Canterbury province because of its high density of Corriedale sheep, can play a major role on the above mentioned early lamb production. Information about Corriedale's onset of the breeding season is scarce throughout the world in comparison with the large amount of data about the Merino and other breeds. In order to get an earlier and concentrated lambing, synchronisation methods have been devised, but these necessitate an accurate knowledge of the breeding season and in particular of its onset. This applies, especially for the case by synchronisation by the ram introduction technique, which at the present is the only practicable method for general term us. The onset of the breeding season for Corriedale in Canterbury has not been precisely determined: the present experiment was planned to provide information on this aspect of the reproductive process. Several methods can be utilized for determination of the breeding season of ewes. The possibility of obtaining information from a number of flocks belonging to different properties and the large number of animals involved decided the utilization of the examination of reproductive organs of slaughtered ewes technique. By means of this method information of the presentation of heats and thus approximate date of ovulation cannot be obtained: on the other hand it permits the consideration of a large number of animals. Date of ovulation can be determined with a relative precision from examination of the ovaries. The presence of the ram can alter the onset of the breeding season (see Chapter II, page 7) thus for a determination of the natural onset all ewes to be slaughtered were kept away from rams. It was intended to continue the observations throughout the breeding season, but, due to problems in the availability of animals, this was not done and only the onset was able to be determined.