Four groups of eight Hampshire × Duroc crossbred gilts were laparotomized at 5 months of age to remove either one ovary (Group O), one uterine horn (Group H), one ovary and the adjacent horn (Group O+H), or sham laparotomy (Group C). The gilts were bred at 10 months of age. The purpose was to compare effects of uterine crowding and altered numbers of corpora lutea (CL) to embryo ratios on CL progesterone, excretion of steroid metabolites in urine and embryo survival at 27 to 35 days of gestation. Urinary metabolites of progesterone (pregnanes) and estrogen, and CL progesterone were quantified by gas-liquid chromatography. Percentages pregnant among mated gilts were nonsignificant between groups. Compensatory hypertrophy of the remaining ovary in Groups O and O+H averaged 85%, 67% and 90%, respectively, for weight of CL and ovary, and number of CL as compared to both ovaries of Groups C and H. Group H with one-half as many embryos (P< .01) but comparable to other groups in weight and number of CL and luteal progesterone had no dead embryos which was significantly (P< .05) less than Group O+H. Increased embryo death in Group O+H was attributed to limited uterine space since each remaining horn contained 9 to 13 embryos. The within groups correlation between dead embryos and total embryos in each horn was 0.40 (P< .01). Average excretion of urinary pregnanes was highest (P< .05) in Group H but estrone excretion was similar to the other groups on Days 26 to 27 of pregnancy. Excretion of pregnanes but not estrone per viable embryo was nearly 3 times greater in Group H as compared to the other groups (P< .01). The latter result shows that the number of fetal-placental units was more closely related to estrone metabolism than to progesterone metabolism. There was no evidence that increased availability of CL progesterone or its increased metabolism per viable embryo as in Group H influenced ova loss (CL-total embryos).
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Monk et al. (1974) studied this question.