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    An investigation into the mechanisms involved in the depression of ovulation rates in ewes grazing oestrogenic lucerne : a thesis peresented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1978) McLeod, Bernard Joseph
    The reproductive performance of 123 Romney and Border Leicester x Romney ewes was compared after they grazed oestrogenic lucerne or non-oestrogenic ryegrass/clover pasture. To synchronize oestrus prior to the experimental treatment, progestagen-impregnated intravaginal sponges were inserted in all ewes for 14 days. In Experiment I, which involved 42 Romney and Border Leicester x Romney ewes, the animals grazed treatment pastures for one complete oestrous cycle. Blood samples were taken at intervals throughout the cycle and luteinizing hormone concentrations were determined. Ovulation rates and the numbers of follicles present on the surface of the ovaries were recorded at laparotomy, three days post-oestrus. In Experiment II, which involved 81 Romney ewes, oestrogenic lucerne or non-oestrogenic ryegrass/clover pasture was grazed for a complete oestrous cycle, or treatments were interchanged in mid-cycle. All ewes were slaughtered three days post-oestrus and their reproductive tracts were recovered and individually identified. Ovulation rates and the numbers of follicles on the surface of the ovaries were recorded. After sectioning the ovaries, all follicles of a diameter greater than 2.0mm were recorded. Sections of tissue from the vagina, cervix, uterus and fallopian tubes of each ewe were mounted, stained with haematoxylin and eosin, and the height of their epithelial cells measured. The ingestion of oestrogenic lucerne for one complete oestrous cycle depressed ovulation rates by 29 percent (0.67 ovulations per ewe) in Experiment I and by 22 percent (0.40 ovulations per ewe) in Experiment II. The ingestion of oestrogenic lucerne for part of the oestrous cycle, depressed ovulation rates only if it was consumed for the latter half of the cycle. Oestrogenic lucerne did not significantly influence the secretion of luteinizing hormone over the pre-ovulatory period, or at any other stage of the oestrous cycle. There were no significant differences in the total numbers of ovarian follicles present, in the numbers of follicles on the surface of the ovaries, or in the numbers of large follicles (with a diameter of greater than 3.5mm) present, between the treatment groups. The ingestion of oestrogenic lucerne did not increase significantly, the height of epithelial cells in genital tract tissue, when compared with that in ewes grazing non-oestrogenic ryegrass/clover pasture. Similarly, there was no significant difference in uterine weights. This is in contrast to published data where lucerne is fed to speyed ewes.
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    The genetic basis of growth, oestrous behaviour and fertility in Romney Marsh ewes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University
    (Massey University, 1967) Ch'ang, Tang Seng
    The rate of reproduction or fertility of the ewe in a breeding flock determines not only the number of surplus animals available for sale as a source of income but in addition, affects the scope of selection for improvement in all productive characters. The ewe's fertility therefore is a character whose economic significance is more nearly matched by its biological ramifications than other attributes of the sheep. The extensive usage of the Romney Marsh breed in New Zealand both in breeding flocks and as the basic ewe breed for meat production only adds importance to the need for higher fertility among the ewes of this breed. Although it is known that under New Zealand conditions, Romney ewes can be mated as hoggets (between four and 14 months in age) for lamb production (Apps 1953; Lewis 1959), the common practice is to delay first mating until they are on average about 18 months old. This system of flock management has a two-fold effect on improvement of fertility by mass selection. First, selection for fertility can not take place until after the first lambing and second, being a corollary of the first, the annual rate of genetic gain in fertility is reduced by the increase in generation interval. Therefore, so long as the current system of flock management remains in practice, there is an obvious need to investigate hogget characters which may be used as criteria of potential fertility at the time of selection for replacements when the ewes are less than 18 months old.