Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354107
Title: Maternal factors affecting early pregnancy in sheep
Author: Ashworth, Cheryl J.
ISNI:       0000 0001 3430 6639
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1985
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Abstract:
Embryonic mortality imposes a severe limitation to reproductive efficiency in the domestic species. In sheep, 20% to 30% of conceptions are not represented by lambs at birth. Attempts to improve embryonic survival by alterations to nutritional regimes and by control of other environmental factors have achieved only limited success. It has been suggested that some embryos may die because of an inappropriate uterine environment. The experiments described in this thesis investigated physiological mechanisms occurring during early pregnancy in the ewe. Knowledge of such factors may elucidate some causes of embryonic wastage and highlight potential means of improving embryonic survival. This thesis examined two aspects of maternal function during early pregnancy; luteal function, and the relationship between the developing embryo and the uterus. An association between the progesterone profile after mating and embryonic survival was observed. Pregnancies during which all embryos survived had higher progesterone concentrations from the day after mating, relative to pregnancies associated with embryonic mortality. This experiment also revealed complex inter-relationships between several factors known to affect embryonic loss. Reduced fertility late in the breeding season could be explained entirely by differences in progesterone concentration. The progesterone profile was highly variable both between ewes, and within ewes during successive pregnancies. The repeatability estimates for pre-luteal and luteal-phase progesterone concentrations suggested that the response to selection for a particular progesterone profile would be low. Luteal-phase progesterone secretion was pharmacologically suppressed in order to mimic the changes in progesterone concentration which may occur following environmental stress. Treatments which lowered progesterone levels also reduced embryonic survival. The composition of uterine fluids was investigated in cyclic and pregnant ewes, and in ovariectomised ewes receiving exogenous steroids. Concentrations of several enzymes varied throughout the oestrous cycle. These changes were considered to reflect ovarian steroid concentrations. Differences in the levels of uterine proteins were observed between pregnant and non-pregnant ewes, and between the gravid and non-gravid horn of unilaterally pregnant ewes. Variations in the schedule of steroid administration to ovariectomised ewes affected the relative concentrations of several uterine components. The potential mechanisms by which such differences may arise were discussed. The experiments described in this thesis have revealed associations between maternal factors and embryonic survival. Potential means of improving embryonic survival arising from these observations were described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.354107  DOI: Not available
Keywords: Human anatomy & human histology
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