CHROMOSOMAL ANALYSIS OF 159 BOVINE EMBRYOS COLLECTED 12 to 18 DAYS AFTER ESTRUS

Abstract

One hundred and fifty-nine embryos were analysed in conjunction with embryo transfer studies. Chromosome preparations were made from small biopsy fragments of trophoblast, from large portions of trophoblast and the inner cell mass, or from the entire embryo. Results obtained from fragments were similar to those obtained from large portions of trophoblast and inner cell mass. No structural chromosomal abnormalities were observed. Single triploid, diploid-triploid and diploid-hexaploid and 66 diploid-tetraploid embryos were found. The 41.5% incidence of diploid-tetraploid embryos was relatively high, and appeared to be associated with a donor factor. The transfer of 49 biopsied and analysed embryos to recipients resulted in 15 pregnancies, seven with diploid-tetraploid embryos having up to 25% of polyploid cells. The diploid-triploid and diploid-hexaploid embryos were among the transfers that did not result in pregnancy. The low incidence of embryos with chromosomal abnormalities, excluding the diploid-tetraploid embryos, may have been due to the embryos being analysed at 12 to 18 days of age rather than at an earlier age before death or degeneration could have occurred.

Karyotypes of 3- or 4-day-old pig embryos after short in-vitro culture

“…For the pig, the initial claim that chromosome abnormalities are very common among 10-day-old pig blastocysts (McFeely, 1967) has not been substantiated by sub¬ sequent research. In cattle, no abnormalities besides mosaicism with a polyploid cell line have been recorded (Hare et al, 1980; see also 'Discussion'). Aneuploid sheep embryos have been found at a frequency of 4-7% (Long & Williams, 1980).…”

“…The chromosomes of preimplantation embryos from chromosomally normal parents have been studied for 10-day-old pig blastocysts (McFeely, 1967;Dolch & Chrisman, 1981;Long & Williams, 1982), 12-18-day-old cow blastocysts (Hare et al, 1980) and 2-4-cell stages of sheep embryos (Long & Williams, 1980). For the pig, the initial claim that chromosome abnormalities are very common among 10-day-old pig blastocysts (McFeely, 1967) has not been substantiated by sub¬ sequent research.…”

Effect of Administration with Low-dose FSH to Recipient Cows on Embryonic Survival after Bilateral Nonsurgical Embryo Transfer.

“…In general, early embryonic loss could result from chromosomal abnormalities. However, the proportions of these abnormalities appeared to be much less than the early embryonic loss rate [36,37], even in the case of in vitro-produced embryos [38]. It is further concluded that chromosomal abnormalities do not explain the high rate of early embryonic loss.…”

Factors affecting embryo survival and strategies to reduce embryonic mortality in cattle

“…Recent studies using fluorescence in situ hybridization with chromosomespecific probes for analysis of chromosomes in in vivodeveloped bovine embryos revealed that mixoploidy, i.e., the presence of a mixture of diploid and polyploid cells, increased from 5% on Day 2 to up to 31% on Day 5 (Viuff et al 2001), while 25% of cattle embryos at Days 7-8 were mixoploid, but with generally less than 10% polyploid cells (Viuff et al 1999). If, as suggested by Hare et al (1980), up to 25% polyploid cells in the trophoblast of Day 12-18 embryos is compatible with pregnancy, mixoploidy would account for only a minor percentage of embryo losses in cattle. The "true" polyploid embryos, when all the cells are polyploid, would be eliminated before they cleave beyond the eight-cell stage .…”