Producers using artificial insemination on cows or heifers often might need to transport the cattle to summer grazing following AI service. Researchers at South Dakota StateUniversity urge care, however, noting that moving bred females at the wrong time can negatively affect reproduction.

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.

Table 1

Time course of early bovine embryo development

Event                                                                             Day

Estrus                                                                            0

Ovulation                                                                       1

Fertilization                                                                      1

First cell division                                                            2

8-cell stage                                                                    3

Migration to uterus                                                         5-6

Blastocyst                                                                      7-8

Hatching                                                                        9-11

Maternal recognition of pregnancy                           15-17

Attachment to the uterus                                             19

Adhesion to uterus                                                       21-22

Placentation                                                                   25

Definitive attachment of the embryo to the uterus  42

Birth                                                                               285


Table 2

Time points for shipping pregnant cattle



When to ship                             1 – 4 or after 45 to 60

When not to ship                      6 – 42


Source: South Dakota  StateUniversity