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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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    A study of transcervical artificial insemination in sheep
    (Massey University, 1995) Usboko, Yohanes
    The study describes two trials on artificial insemination in Romney ewes. Trial 1 was conducted to examine the anatomical site in the reproductive tract of the inseminating needle after transcervical insemination, and to evaluate the effect of the needle in causing cervical tissue damage based on the microscopic assessment of cervical slides. Trial 2 was undertaken to compare the effect of intrauterine, cervical or transcervical methods of insemination with fresh semen on fertility. Two hundred and five mixed-aged ewes (3-8 years old) were hormonally treated with CIDR-G for 12 days and these were removed after this period. Forty-eight hours later, to monitor the onset of oestrus, they were joined with 10 harnessed vasectomised rams. Oestrous detection was undertaken twice daily, at 1.00 am and 1.00 pm. Most ewes were synchronised in oestrus over 2 days after CIDR withdrawal but there was an extended period of 'second' oestrus when the inseminations were conducted. In Trial 1, transcervical insemination with Indian ink was performed in 29 ewes at the second oestrus, and then they were euthanased with Sodium Pentobarbitone. Position of the inseminating needle in situ was determined at dissection. The genital tract was removed and the uterus opened to determine whether Indian ink had penetrated. The cervix was then split into three similar sized portions, fixed in Bouins solution, and sections histologically processed and stained for slides. The slides were microscopically examined by two evaluators to determine damage scores. In trial 2, semen samples (concentration at least 3 x 109 spermatozoa ml-1, motility minimal 4) were collected per artificial vagina from 5 Romney rams, pooled and freshly diluted with UHT-milk to 8 x 108 spermatozoa ml-1. One hundred and seventy-five cyclic ewes were randomly assigned to either of three AI techniques (intrauterine, cervical and transcervical), and were inseminated with freshly diluted semen at a mean interval of 6.1 0.26 h after second oestrus was detected. In slaughtered ewes, penetration of the modified needle through the lumen of the cervix and even into the uterus occurred more that with the unmodified needle (90% vs 68%; 0.05
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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.
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    Some aspects of dystocia in sheep with particular reference to Romney stud ewes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University
    (Massey University, 1975) McSporran, Keith David
    Three studies were undertaken to investigate dystocia in Romney stud ewes. In the initial study an analysis was made of 4,400 individual performance records collected over a period of nine years from a Romney stud flock. On the basis of the records, dystocia in the flock was attributed to a physical disproportion between the lamb and the maternal pelvis, and its incidence was shown to be highly correlated with the mean birth weight of single lambs (r=0.84). Dystocia appeared to be unrelated to the effects of parity, weight at mating, or litter size of ewes. A high repeatability of the condition was demonstrated. Differences between sires with respect to dystocia in their progeny at birth were demonstrated in some years and were shown to be related to lamb weight, such that those sire groups with higher average lamb weight experienced the greatest incidence of dystocia. The decline in the incidence of dystocia, apparent from the records, was attributed to a reduction in mean birth weight of lambs and a possible increase in pelvic dimensions of the ewes, brought about by selective breeding. Secondly, a tocometric study of 18 Romney ewes was made using intra-amniotic open ended catheters and intra-abdominal balloons implanted at laparotomy. Dystocia occurred in 12 ewes and, with the exception of one ewe that developed uterine inertia, was associated with abnormalities in presentation, position or posture (maldisposition) of the lamb at birth. By comparison, the presentation, position and posture (disposition) of the lambs born to the eutocous ewes was normal. A significant difference in birth weight of lambs was demonstrated between ewes that gave birth to lambs in normal disposition as opposed to those that gave birth to maldisposed lambs, and between ewes that experienced eutocia and dystocia. Uterine activity during late pregnancy, characterised by alternate periods of activity and quiescence, was not related to the disposition of the lamb at birth. During first stage labour uterine activity was higher in those ewes that experienced dystocia. However, this was considered to be a reflection of the higher lamb birth weight in this group as birth weight was correlated with uterine activity during the final three hours of first stage labour. Low abdominal bearing down effort was thought to contribute to the lack of progress during parturition in three ewes with posteriorly presented foetuses. Except for one case of uterine inertia, low uterine pressures or abdominal bearing down effort was not implicated as a primary cause of dystocia in these ewes. In the final study a method of radiographic pelvimetry was developed which was used to study the relationship between pelvic size and lamb size at birth in ewes with histories of eutocia and dystocia. In addition, three different age groups of ewes were radiographed to provide information on changes in pelvic dimensions with age. Large differences in respect to the relationship between estimated area of the pelvic inlet and the size of the lamb were demonstrated between ewes with histories of eutocia and dystocia. The relatively large pelvic area of the eutocous ewes was considered to be largely responsible for differences in the recorded incidence of dystocia between the groups. Estimates of correlations between internal and external pelvic measurements taken from the radiographs were thought to be too low to be of practical use in selection for larger internal pelvic area. Furthermore the relationship between internal and external pelvic measurements was found to alter with age in some cases, indicating that the effect of age on these relationships would have to be examined further if selection by means of external pelvic measurements were to be attempted. As a result of these investigations, the hypothesis was advanced that dystocia in Romney stud ewes is commonly caused either by the relatively small size of the pelvic inlet of the ewe, or the relatively large size of the lamb, or both. There were indications from the first and third studies that the flock incidence of dystocia can be reduced by genetic selection.