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  • Author: L. C. ULBERG x
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C. O. WOODY and L. C. ULBERG

Summary.

Attempts to obtain fertilization of sheep ova recovered from follicles and deposited in the oviducts of the same ewes were unsuccessful. The recovery and transfer of postovulatory one-cell ova was successful if the paired ewes were closely synchronized as to the end of oestrus. Fertilization apparently was completed soon after the end of oestrus in mated ewes and ova from non-mated ewes were apparently still capable of normal fertilization and development at this time. Ova from non-mated ewes usually do not have corona cells present when recovered from the oviduct. Both fertilized and unfertilized ova appear to be able to withstand stress associated with a single transfer, but a second transfer greatly reduces the chances of a successful pregnancy.

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C. O. WOODY and L. C. ULBERG

Summary.

No difference was found in the viability of unfertilized sheep ova transferred from donors maintained at 70 or 90° F to mated recipients maintained in constant 70° F. However, reciprocal transfers of fertilized ova indicated that the reproductive tract of ewes maintained at 90° F did not provide as favourable an environment for embryo development as did the tract of ewes maintained at 70° F. Control ewes maintained in constant 70° F had a significantly higher level of fertility than ewes maintained in a room with constant 90° F. Data obtained from ewes shifted from one air temperature to another indicated that most of the decrease in fertility due to the high air temperature had occurred by the end of oestrus in these ewes. Differences were noted in the fertility of two age groups of ewes, but this difference did not affect the ova before fertilization as indicated by transfer of ova between groups.

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J. H. BRITT and L. C. ULBERG

Oestrous synchronization in cattle has not received widespread acceptance because of a period of transitory infertility which occurs following progestagen withdrawal. This reduced fertility has been attributed to changes in the time required for sperm capacitation (Lauderdale & Erickson, 1970), changes in the amount and physicochemical characteristics of cervical mucus (Johnson & Ulberg, 1965; Hill, Lamond, Henricks, Dickey & Niswender, 1971), changes in body temperature (Johnson & Ulberg, 1965; Long, Nipper & Vincent, 1969), reduced fertilization rate (Wagner, Veenhuizen, Gregory & Tonkinson, 1968), and histochemical changes in the endometrium (Wordinger, Dickey & Hill, 1970). All of these physiological aberrations can be attributed to hormonal changes. This experiment was conducted to determine changes in peripheral blood plasma progesterone concentration during and subsequent to oestrous synchronization with melengestrol acetate (MGA—The Upjohn Company) and to compare

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P. J. BURFENING and L. C. ULBERG

Summary.

Following a preliminary experiment, split ejaculates of rabbit semen, incubated for 3 hr at 38° or 40° C, were examined and inseminated separately into the uterine horns of rabbits mated 4 hr previously to vasectomized males. Eggs were recovered and examined for evidence of fertilization 30 hr post coitum. Following return of the eggs to the oviduct their survival was estimated by counting the implantation sites at 9 days post coitum. There was no evidence of any effect of treatment temperature on fertilizing capacity of semen, but embryonic survival rate was higher (75%) in horns inseminated with semen incubated at 38 ° C than in those inseminated with semen incubated at 40° C (53%). Neither fertilization rate nor embryonic survival rate was significantly correlated with semen quality.

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C. W. ALLISTON, B. HOWARTH Jr. and L. C. ULBERG

Summary.

In-vitro culture of 1-cell fertilized rabbit ova for 6 hr at a temperature corresponding to elevated body temperature (40°C) resulted in increased post-implantation embryonic mortality following the transfer of such eggs to synchronous pseudopregnant females. This increased mortality was not observed when culture temperatures corresponded to normal body temperature (38° C) or in cultures that were begun after completion of the first cleavage.

It is concluded that the early rabbit embryo is directly affected by the increased maternal body temperature that accompanies thermal stress of the female. Such effects may not become apparent until the late stages of embryonic development.

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Barbara S. Durrant, E. J. Eisen and L. C. Ulberg

Summary. Single trait selection of mice for either large body size or large litter size resulted in an increased ovulation rate because of possible enhanced ovarian sensitivity to gonadotrophins. There was no difference in pre-implantation embryonic survival in either of the selected lines when compared to control mice. Selection for body weight did not alter post-implantation embryo survival, but fewer fetuses were lost after implantation in the litter size line compared to the control line. Index selection for large body size and small litter size did not change ovulation rate but increased pre- and post-implantation embryonic mortality. Selection for small body size and large litter size increased ovulation rate and decreased early embryonic death.

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R. W. MOORE, E. J. EISEN and L. C. ULBERG

Summary.

Intra- and inter-line transfers of blastocysts were performed between two lines of mice selected for high (H6) and low (L6) body weight at 6 weeks of age. A greater percentage of L6 blastocysts survived to term than did H6 blastocysts (7·8%, P < 0·01) and more L6 recipients littered than did the H6 recipients (19·7%, P < 0·01). A greater percentage of the mice born to the L6 recipients was found alive at birth (8·5%, P < 0·05), as was a greater percentage of the young carried in the uteri of the opposite line (8·3%, P < 0·05).

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D. S. ELLIOTT, J. E. LEGATES and L. C. ULBERG

Summary.

Low fertility in mice selected for small body size (L) at 6 weeks of age was due to fewer matings, more ovulation failures in females mating, a lower ovulation rate and a lower fertilization rate than in unselected mice (C2) maintained as a control. The L males apparently had less libido than C2 males. This may have contributed to fewer matings in the L line. Failure to mate or failure to ovulate, if mating, could not be explained by differences in age or in body weight. It is suggested that a thyroid deficiency was responsible.

Females of the line selected for large body size (H) at 6 weeks of age ovulated more ova than C2 females. Essentially no foetal death occurred, after implantation, except in the H line. A lower percentage of the foetuses was living at 18 days of gestation in females of this line than in the females of the C2 line.

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FULLER W. BAZER, A. J. CLAWSON, O. W. ROBISON and L. C. ULBERG

A review of the literature indicates that injection of gonadotrophic hormones or giving high-level-energy feeds will markedly increase the number of ovulations in polytocous animals. Higher ovulations rates are then followed by an increase in the precentage of embroys which die in utero. This increased embryonic death may be due either to inherent limitations within the individual embryo or to maternal limitations which affect the litter (Runner, 1951). In any event, the number of young at term reamins at a level characteristic for the species. Empbryonic death usually occurs before the time of attachment of the embryo to the endometrium (Boyd, 1965).

Attempts to increase the number of young born either by hormonal superovulation(Flower & Edwards, 1957; Adams, 1960; Hafez, 1964) or by the addition of embryos to the uterine horns (McLaren & Michine, 1959; Adams, 1960) have seldom been sucessful. In some