In the 1970s, bovine embryo transfer (ET) shifted from research in a laboratory environment to commercialization of this technology for beef producers. With the quarantine requirements and expense of importing Continental breeds of cattle from Europe, embryo transfer became the logical means to reproduce greater numbers of these animals at a lower cost. The ET industry grew very rapidly and soon would become what it is today, a common practice utilized by select ranchers and breeders. Research over the years has primarily focused on methods to increase the number of ovulations and fertilized ova from the donor female, but the total number of transferable embryos has not changed markedly in the last 20 years. More recent advances have been in the area of in vitro production of embryos that allow for greater numbers of embryos to be produced and easier accessibility to incorporate technologies such as sexed sperm, sperm injection, or transgenics. This paper will focus on the second part of the equation, the recipient, and decisions that will enable both the customers and practitioners to most efficiently utilize embryos from superovulation, in vitro production, or nuclear transfer, so that the maximum number of pregnancies can be produced.

Progesterone concentrations in systemic blood were determined by radioimmunoassay in crossbred cattle used as recipients in an embryo transfer programme. An embryo was transferred surgically to the uterine horn of 528 females which were in oestrus within one half-day of the donor. Jugular blood was obtained at the time embryos were transferred (3-7 days after oestrus) and again from most females between Days 9 and 14. Pregnancy was determined by rectal palpation 45-65 days after oestrus. There were no significant differences between serum progesterone levels of females which remained pregnant and those which did not. Out of 177 pregnant recipients, none had serum progesterone levels less than 0.5 ng/ml on Days 10, 11, or 12 but in 8, values were less than 1.0 ng/ml. Blood samples were also taken on Days 20, 21, or 22 from 113 of these recipients. The mean +/- s.e.m. concentration of progesterone in the pregnant females (5.14 +/- 0.34 ng/ml) was significantly higher (P less than 0.001) than in the non-pregnant females (1.17 +/- 0.25 ng/ml). The correlation coefficients between progesterone levels on Days 3, 4, 5 or 6 and 10-12 ranged from 0.18 to 0.37 (all P less than 0.02). Progesterone levels were not related to length of the previous cycle, the time of day an animal was first noticed in oestrus or the side of the corpus luteum. However, cows with a short oestrus had higher progesterone levels on Days 3-7 (P less than 0.01) than those in oestrus for a longer time.

Kafi, M., McGowan, M.R., 1997. Factors associated with variation in the superovulatory response of cattle. Anim. Reprod. Sci. Variability in the superovulatory response of cattle is still one of the major limiting factors in extensive usage of embryo transfer technology. A variety of approaches including recent attempts to eliminate the suppressive effect of the dominant follicle have been used to reduce the unpredictability of the superovulatory response of cattle. The development of techniques such as transrectal ultrasonography, have enabled a re-evaluation of ovarian dynamics during superovulation of cattle. In addition, advances in reproductive hormone assays have increased knowledge of the mechanisms controlling follicular development, ovulation and corpus luteum function. This review focuses on the current understanding of factors affecting the superovulatory response of cattle. Also, abnormalities of ovulation and endocrine disorders that may occur during superovulation are reviewed.

Pregnancy rates were compared between fertile and infertile donors in an embryo transfer program. Non-surgical embryo transfer techniques were utilized for examination of uterine contents and collection of ova. Recovered embryos were transferred surgically into suitable recipients. Three groups of donors were included in this investigation: a) fertile; b) infertile, due to known causes (diagnosed); c) infertile, due to unknown causes (undiagnosed). There were 11.3, 6.6 and 8.0 corpora lutea; 6.8, 1.2 and 1.0 fertilized ova; 3.6, 0.8 and 0.4 pregnancies per superovulation for the fertile, diagnosed and undiagnosed groups, respectively. In 23 months, unsuperovulated, fertile, diagnosed and undiagnosed donors yielded 17, 15 and 9 fertilized ova which resulted in 15, 13, and 3 pregnancies, respectively. Donors treated for uterine infections, adhesions or cystic ovaries prior to superovulation responded with 10.1, 7.6 and 4.1 corpora lutea; 1.9, 4.0 and 0.3 fertilized ova; 1.1, 3.3 and 0.2 pregnancies per superovulation, respectively. Relatively few viable embryos were recovered from donors with chronic cystic ovaries or from infertile cows of unknown etiology. Infertile donors, when compared to fertile donors, were unproductive when used for embryo transfer.

To determine the effect of heterospermic insemination on fertility in Exp. I, albino does were artificially inseminated homospermically with semen from two albino and two homozygous colored bucks and heterospermically with all 11 possible combinations of their semen. Mean pregnancy rates from 206 inseminations were 49, 63, 57 and 42% for insemination doses with one, two, three and four males contributing. There was a quadratic effect (P<.01) of the number of males on pregnancy rate. For does allowed to kindle, the number of offspring per doe inseminated was 2.1, 3.2, 3.5 and 2.0 from mixtures containing spermatozoa from one, two, three and four males; similarly, the percentage of cleaved embryos recovered from sacrificed does was 32.7, 47.7, 37.6 and 32.8. Deviations (P<.05) were observed from the expected 1:1 ratio of offspring from all four mixtures of semen from one albino and one colored buck. In experiment II, 150 does were inseminated with doses containing semen from one, three or five males. The pregnancy rates were 74, 80 and 78% for inseminations with semen from one, three and five males, and the number of offspring per doe inseminated was 4.2, 5.3 and 4.4, respectively, with a quadratic effect (P<.10) of the number of males contributing to the seminal mixture on the number of offspring per doe.

Two nonsurgical techniques for embryo recovery were employed and used in Days 6 and 7 of the estrous cycle. A significant difference between techniques was observed in both days of collection, with the closed system being more efficient in Day 6 and the opened one more efficient in Day 7. The bacteriological contamination of flushing medium (11% for the closed system and 21% for the opened technique) was of saprophytic bacteria and did not affect the percentage of pregnancies in either system.

A total of 511 embryos was recovered non-surgically from nearly 100 superovulated or untreated donors. Superovulation with FSH-LH resulted in more corpora lutea, recovered ova, and pregnancies (P<.01) than superovulation with PMSG. No differences were observed in numbers of ovulations, embryos recovered, or pregnancies per donor when prostaglandin F2α was given to donors 2 versus 3 days following gonadotrophin treatment.

In 1971, 1972 and 1973 cattle were inseminated with frozen semen from three individual bulls (homospermic) and seminal mixtures from these bulls (heterospermic). Post-thaw spermatozoan motility in heterospermic treatments was not superior to homospermic treatments. The number of motile spermatozoa after thawing ranged from 7.4 to 12.1 × 106 per inseminate but less than 2% of the variability in first-service pregnancy rate was due to spermatozoal numbers. No signiFicant increase in fertility was obtained when insemination with mixtures of semen from two bulls was compared to homospermic insemination. The first-service pregnancy rate of 70.6% for 323 services with the seminal mixtures from three bulls was significantly higher (P < .05) than the 62.7% for 327 homospermic inseminations or 62.2% for 323 services with the seminal mixtures from two bulls. The overall mean pregnancy rate (first and second services combined) for the triple-seminal mixtures was higher than the single and double-seminal mixtures for each group of cattle inseminated. Heterospermic inseminations with frozen semen resulted in a deviation from the expected equal number of progeny per sire.