Pregnancy Determination in Cattle
Pregnancy determination is recommended to maximize breeding efficiency. In beef herds, the breeding season (natural service or AI) is ideally fixed at a length of 60–70 days. This gives the average cow two or three services to conceive. Cows that are not pregnant or were bred late should be identified; if kept in the herd, they will calve later in the season. Maintenance costs are significant, although they vary widely by farm and by year.
Pregnancy determination of beef cows should be done shortly after the breeding season is over (eg, 45–60 days); if the breeding season starts June 1 and ends early in August, it can be done during late September while the cows still have plenty of flesh from summer pasture. It is then possible to profitably market nonpregnant cows before expensive winter feeding starts. When excessive returns are noted or bull performance issues are suspected, early pregnancy determination by ultrasound 50 days after the start of the breeding season can be invaluable. A target of 65% of cows should be pregnant to the first cycle in beef herds, and so by 50 days this can be measured as pregnancy determination success 30 days after breeding. Supplementary AI or new bull power can be implemented with poor success, alongside further investigation.
Dairy cows should be examined to determine their pregnancy status and if found open can be synchronized into estrus with prostaglandin F2α, or timed AI. In cows that are open or that have not been detected in heat, the decision on which hormones to use to induce estrus is based on evaluating the ovaries for CL, follicles, and ovarian cysts. The most common method to determine pregnancy and evaluate ovaries is transrectal palpation and, increasingly, the use of ultrasonography. Ultrasonography may have the following advantages: 1) Nonpregnant cows can be found earlier (28–32 days after breeding), and diagnostic information on the status of the ovaries and uterus can be obtained. 2) The viability of the embryo or fetus can be assessed, eg, by visualization of a fetal heart beat. 3) Twins are more readily detected. 4) Sex of the fetus can be determined. 5) Age of the conceptus can be estimated more accurately. 6) The producer can be shown the conceptus, which could be reassuring in herd cases of embryonic losses.
Other herd health examinations should be considered while the cows are being checked for pregnancy. These include an accurate evaluation of body condition, the reproductive tract, teats and udder, feet and legs, teeth, and early neoplastic eye lesions. Vaccinations, internal and external parasite control, and processing of beef calves also can be done at this time.