Graduate Thesis Or Dissertation

Ova tranfers in sheep and rabbits : studies on material influences and irradiation damage

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  • The first study utilized ova transfer in sheep and involved hormonal treatments for synchronization of estrus and superovulation in an investigation of crossbred maternal influences on inbred and linecross lambs. Synchronization of estrus in ewes was achieved effectively with either oral progestogen, 6 α-methyl-17α-hydroxy-progesterone acetate (60 mg./ewe/day), or intramuscular injections of progesterone (10 mg./ewe/day), Satisfactory superovulation was not obtained with pregnant mare serum preparations and alterations in oviduct morphology were noted following oral progestogen therapy. After progesterone injections, superovulation with a mean of 13.4 ovulations per ewe was obtained using pituitary extracts. Successful treatments began day after final progesterone injection with primary injection of 25 mg. followed in two days with 15 mg. of pituitary extract. An intravenous injection of 25 mg. pituitary leutinizing hormone followed at onset of estrus. Twelve Suffolk ewes of three inbred lines were bred to produce fertilized ova from each of three lines and from each possible linecross. Surgical transfers of ova from Suffolk donors were made to nine recipients which were similar in size and consisted genetically of Columbia, Dorset and Cheviot crosses. Based on corpora lutea numbers, in vivo ova recovery rates increased from 39 percent for the first year to 53 percent for the second year. Cleavage rates were 54 and 52 percent for the two years. The inbred line II lamb which developed in a crossbred maternal environment weighed 12.3 percent more at birth than its non-transfer line II counterpart. The transferred linecross III x II lamb weighed 30.6 percent more at birth than its non-transfer counterpart. The linecross took most advantage of prenatal nutrition. Adjusted 120-day weights, condition and conformation scores were similar for transfer and non-transfer lambs at weaning. Under similar postnatal environment, genotype for size is expressed in lambs at weaning. In the second study effects of in vitro x-irradiation of fertilized mammalian ova on their subsequent in vivo development were investigated by means of rabbit ova transfer. Non-irradiated and irradiated two-cell ova were transferred to non-irradiated and irradiated uteri of recipients to discriminate between embryonic and uterine injury. Irradiation was applied to two-cell ova in vitro at levels of 0, 15.4, 61.2, 91.8, and 122.5 rads using a 100 kVp x-ray machine (1 ma., HVL 1 mm. Al., distance 37.4 cm., dose 14.5 r./min.), Ova were transferred into oviducts of prepared recipients. Uteri of recipients were exposed to the same radiation levels as the ova and in addition to 250.2, 265.3, and 530.5 rads. Combination of ova/uterus irradiation showed additive effects of x-ray damage. One step increases of either ova or uterus above 61.2/250.3 rads caused 100 percent embryo mortality Two-cell ova which were given 122.5 rads of irradiation failed to develop into fetuses and uteri which were given 530.5 rads failed to contain implantations. Irradiation with 91.8 rads killed all but the most hardy ova and produced an all or none effect, while 61.2 rads caused abnormal, dead, and resorbed fetuses as well as living offspring. Two such newborn developed latent sequelae in the form of spreading limbs. Deformities became obvious at one month and progressed until death at four months. Histological examinations of eight-day embryos which received 61.2 rads or no irradiation as two-cell ova revealed delayed development in irradiated embryos. Mean spring from increase in weight for the first 50 days of surviving off-spring from irradiated ova was 6 gms./day more than that of controls.
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