A minimum of two different stud colonies should be maintained. A period of 72 hours of celibacy is recommended to obtain peak male breeding efficiency. Female embryo donors should be used between the ages of 3 and 24 weeks, if possible. The best responses to superovulatory stimulation are obtained from females less than 4 weeks of age. Females from different genetic background strains and transgenic lines may yield a wide range of embryo production.
Monogamous breeding is recommended for embryo donor colonies.
Copulation plugs should be checked between 7 and 8 a.m. the morning following breeding. The presence of a plug does not necessarily indicate the deposition of normal sperm within the female tract. It also must be noted that plug-negative females may, in fact, become pregnant. Pregnancy of females carrying very small litters may not be visually apparent. After the compaction phase of development, during the morula stage on ED 2.5, two factors affect the ultimate yield of blastocyst embryos.