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Potential Fertility of Artificially Matured and Ovulated Ova in Cattle

University of Wisconsin

Abstract

Corpora lutea were produced in cattle representing various reproductive stages by injection of pituitary extracts.

Pituitary extracts classified on the basis of bioassay tests as "unfractionated", "parially purified follicle stimulating", and "follicle stimulating", were injected subcutaneously to produce maturation of follicles. In some cases corpora lutea formation was observed from these treatments alone. In other cases the above treatments were followed by a intravenous injection of one of the above extracts or of a "luteinizing" extract. Probably differences of greater significance existed between the efficacy of subcutaneous injection alone and subcutaneous followed by intravenous injection in the production of corpora lutea than between the different types of extracts that were used.

It is doubtful if estrus was produced by the gonadotrophin injections in any case with the exception of a group of 9 cows treated by subcutaneous followed by intravenous injection of follicle stimulating extract beginning 2–9 days after estrus. Four of these cows were in heat within 11–18 days after the preceding heat. Corpus luteum formation occurred also in three of these cows.

It was observed that the greater number of corpora lutea showed the presence of stigmata typical of ovulation. Ova were sought and recovered from the oviducts or from the uterine horns in many cases.

The potential fertility of eggs from artificially matured follicles in immature laboratory animals has now been shown by several workers. The estrual cycle length in cows is greater than in most laboratory animals and this might mean that the time required for normal maturation of the egg might be longer. Under hormonal treatment, however, follicles are matured and ovulated at approximately the same rate in cattle as in laboratory animals. Tests for potential fertility of artificially matured bovine ova were believed to be most critical when made on calves.

No evidence of fertilization was observed in six calves treated and inseminated and slaughtered at 23 to 36 days. In 16 other calves, two and possibly three showed evidence of fertilization. These were slaughtered at 1–4 days after treatment. A two-cell and a three-cell egg and another showing considerable fragmentation were recovered. Potential fertility was thus demonstrated although the percentage observed was quite low.

Of seven cows treated with unfractionated extracts beginning 2–5 days after estrus, none showed evidence of fertility 26–30 days later. Four other cows were treated similarly beginning 14–15 days after estrus. These were observed at 7–20 days; one showed a fragmenting 2-cell ovum and another four 2-cell and one 3-cell ova all fragmenting.

Two cows were treated with a partially purified follicle stimulating extract beginning 15 days after estrus. One of these, killed 55 days later, had a 55 mm. fetus; the other produced a term calf. Although this experiment did not demonstrate the potential fertility of artificially matured and ovulated ova, the treatment at least did not inhibit normal fertility.

Five cows were treated with a follicle stimulating followed by a luteinizing extract beginning 2–3 days after estrus. None showed evidence of fertilization when observed 3–23 days later. Seven other cows were similarly treated but beginning 16–18 days after estrus. Four of these showed evidence of fertilization 29–50 days later. One was diagnosed pregnant by palpation at 43 and again at 50 days. She was palpably not pregnant at 71 days but no abortion was noted. The other three cows were killed on the 46th, 32nd, and 29th days respectively. The number of corpora lutea showing stigmata was 6, 9, and 4. In the first cow three normal fetuses ranging from 26 to 32 mm. were present. A fourth atrophic fetus, 3 mm. in length, was detectable in its small amniotic vesicle. The second cow showed the presence of seven normal fetuses ranging from 10–13 mm. in length, and the third, four fetuses 9–11 mm., also normal.

Under the experimental conditions as provided in the last group of cows, 4 out of the 7 (57 percent) conceived. In three of the cows that conceived, 74 percent of the probable number of eggs were accounted for by normally developing fetuses.