Producers using artificial insemination on cows or heifers often might need to transport the cattle to summer grazing following AI service. Researchers at
Sarah Fields, a graduate research assistant, and SDSU beef reproduction and management specialist George Perry, PhD, say shipping cows between days 5 and 42 post-breeding can be detrimental to embryo survival and cause around a 10 percent decrease in pregnancy rates.
The researchers say critical time points such as blastocyst formation, hatching, maternal recognition of pregnancy and adhesion to the uterus take place during this early time of pregnancy. Stress or disturbance during any of these critical times can lead to increased embryonic mortality and decreased pregnancy rates.
Producers, they conclude, should plan on transporting cattle before the breeding season or immediately after insemination. Shipping within the first four days after insemination is best, they note. The embryo is still in the oviduct during this time and generally not subjected to uterine changes.
By 45 days after breeding, the embryo is well established and fully attached with the placenta, and thus less susceptible to the changes resulting from stress. Shipping at this point is less risky but not entirely safe. Research has shown that shipping cattle 45 to 60 days after insemination can result in 6 percent of embryos being lost.
At any time, Fields and Perry advise producers to use care to reduce the stress involved when animals are shipped. Do not overcrowd trailers and handle cattle as gently and calmly as possible.
Time course of early bovine embryo development
First cell division 2
8-cell stage 3
Migration to uterus 5-6
Maternal recognition of pregnancy 15-17
Attachment to the uterus 19
Adhesion to uterus 21-22
Definitive attachment of the embryo to the uterus 42
Time points for shipping pregnant cattle
When to ship 1 – 4 or after 45 to 60
When not to ship 6 – 42