Currently, there are two chief methods to determine pregnancy diagnosis in cattle: rectal palpation and ultrasound. Both methods have their advantages and, depending on your production system, one may be more beneficial than the other.
Pregnancy diagnosis determined by rectal palpation is the most common method used in the beef industry. The first time a positive pregnancy can be felt is approximately 32 days bred; at this time the embryonic vesicle is the size of a pea.
A veterinarian will compare the size of his/her hand to the entire vesicle, or as it ages, the size of the fetal head. Once a calf has grown to be several months old, age is determined by the size of the head if it can be felt, the size of the placental attachments, and the size of the uterine artery.
After the first couple months of pregnancy, individual calf variation (genetics) will begin to play into the size of the calf, and age estimation begins to be less accurate.
Ultrasound is being used more commonly to aid in diagnosis of pregnancy. A positive pregnancy can be determined by 28 days after breeding. The ultrasonographer will capture an image of the fetal head on the screen and measure its size, allowing for accurate fetal aging.
However, after approximately 90 days bred, the advantage of ultrasound over rectal palpation diminishes, as fetal measurements become less accurate due to individual variation. The earlier a pregnancy is determined via ultrasound, the closer the exact breeding date can be determined. If the goal is to determine AI-bred cows from bull-bred cows, it must be done as early as possible.
|*||Best time to schedule preg check|
|o||Rectal palpation -- if using a 60-day breeding season, approximately 35-45 days after removal of the bull|
|*||In a 60-day breeding season, the oldest fetus will be ~100 days and the youngest will be ~45 days, ensuring an accurate estimation of fetal age|
|o||Ultrasound -- no more than 90 days after turning in bull, especially if determination between AI-bred and bull-bred is needed|
|*||Reasons to preg check|
|o||Less feed costs -- will not need to feed open cows through winter|
|o||Can divide cows into groups based on when they are scheduled to calve|
|o||If a problem occurred, the earlier it is caught, the better chance for determining the cause|
|*||If too many open cows are found, can likely determine between disease outbreak vs. infertile bull|