School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAcute prenatal androgen treatment in sheep( 1994)The steroid environment of the cell nucleus in differentiating mammals is a major determinant of subsequent cellular function. The exogenous manipulation of this environment has resulted in permanent changes in metabolism, behaviour, reproduction, endocrinology and growth. The experiments described in this thesis suggest that an acute exposure to exogenous androgen, established as an intramuscular depot in the gravid ewe, can effect these changes. The growth responses resulting from acute prenatal androgen treatment (APAT) are similar to those reported for chronic androgenization.The undesirable side effects of androgenization, e.g. reduced birthweight, deformed external female genitalia and masculine urination posture, can be avoided with APAT. The literature and the experimental data indicate that mammalian development is strongly influenced by tissue steroid status. Furthermore, the literature and the experimental data suggest that both the timing and duration of the modification of mammalian developmental steroid status (MDSS) affect the response of ovine tissues to androgens. Some of the observed responses appear refractory in nature. The periods of sensitivity to MDSS manipulation differ between tissues and between species. MDSS manipulation via APAT is capable of effecting changes to tissues not normally considered sexually dimorphic, including the ovine pancreas, liver, brain, kidney, bone and wool follicle.
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ItemCytogenetic sex determination of embryos( 1990)The purpose of the research presented in this thesis was to establish a rapid method to allow the cytogenetic determination of sex in sheep embryos. A simplified air-drying technique to allow cytogenetic sex determination initially established in mouse embryos. These techniques were then applied to sheep embryos. The techniques involved treating embryos with three types of fixatives :- fixing solution, softening solution and drying solution. Methanol : glacial acetic acid
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ItemIntake and utilization of a barley supplement treated with virginiamycin by gestating and lactating ewes( 1991)A pen feeding study was conducted to evaluate the influence of virginiamycin (40 g virginiamycin/tonne barley ) on the production of pregnant and lactating ewes fed barley supplement. Twelve single and sixteen twin-bearing ewes were randomly allocated to one . of 3 groups to receive either lupins, barley or barley plus virginiamycin (BVM), fed for 3 weeks before and 3 weeks after lambing. During late pregnancy, feed intakes in ewes carrying twins were not altered by treatments. Mean liveweights at parturition of the barley-supplemented 'ewes. were below than those of the other groups (p=0.14). Feed conversion efficiency was significantly improved (p=0.05) in the lupin and BVM groups as compared to the barley supplemented ewes. The condition score of the ewes was not improved by supplementation and type of supplement had no effects on body condition score loss. Mean retention time of Cr-hay in the GI tract was increased (p<0.05) by supplementation with virginiamycin treated grain. However the dry matter digestibility on the BVM diet was not improved (p<0.05) as compared to the lupin supplemented ewes. The performance of ewes carrying singles was generally unaffected by treatment (p>0.1). The. exception occurred during lactation, where the barley-supplemented ewes lost more weight than the other groups (p<0.05). Differences in the mean birth weight of twin lambs were significant (p=0.05) while those of lambs born as singles was not significant. Twin lambs from ewes fed barley showed significantly higher mortality (p<0.01) than lambs born to ewes in lupin and BVM groups. However , no single born lambs in any group died from birth to 42 days of age. No significant differences were found between total milk yields of ewes nursing either twin or single lambs. The yield of milk fat from ewes nursing twins in lupin group was significantly higher (p<0.05) at day 20 of lactation than the other groups. The results suggest that lupin grain was not superior to barley grain plus virginiamycin as a supplement for gestating and lactating ewes carrying twin lambs fed hay as a basal diet. However, on the basis of cost, barley plus virginiamycin would generally be prefered.