Cattle producers and veterinarians long have relied on one single method for determining pregnancy in their cows, but recent changes in technology have expanded the options considerably.
Pregnancy diagnosis by rectal palpation has been performed for decades in cattle. This of course involves an experienced person introducing their hand and arm into the rectum of the cow or heifer and physically feeling the fetus. A skillful palpator can diagnose pregnancy as early as 40 days of gestation and later. It is usually possible to determine the gestation length (or fetal age), although the variation in size of individual fetuses makes it somewhat more difficult as the fetus gets larger. In general, though, a veterinarian can do a decent job of determining the age of a fetus less than 4 months along. Rectal palpation is quick, requires no specialized equipment, gives instant results, and is the most economical of all methods. In addition, rectal palpation can help diagnose pathologic problems within the pelvis and abdomen.
Ultrasound examination of the uterus has been employed for the past 15 years or so by veterinarians. Advances and availability in equipment has resulted in most veterinary clinics being able to offer this service. In this method, an ultrasound probe is inserted into the rectum for examination of the uterus. Ultrasound has the advantage of being able to determine sex of the fetus; however, there is a fairly narrow window in which this can be accomplished (between 55 and 70 days, in general). Ultrasound also has the advantage of being able to detect pregnancy earlier than palpation—as early as 28 days of gestation. Determining the age of the fetus is more accurately performed with ultrasound versus palpation, allowing cattle producers to differentiate between AI and bull bred pregnancies, and to group females by future calving dates. Ultrasound requires expensive equipment and considerable skill, and is more expensive than palpation. Certain operations, seedstock operations, for example, may find value in the ultrasound’s ability to obtain accurate ages and sexes of the calves about to be born.
The most recent advance in pregnancy diagnosis involves use of blood tests. Pregnant cattle have relatively high levels of certain pregnancy specific proteins, or PSPs, in their bloodstream. Blood tests have been developed to detect this protein, and one is now offered at the SDSU ADRDL. For this test, the PSP becomes elevated in cattle serum at approximately 28 days of gestation, and lasts until calving. One disadvantage to these methods is that PSP levels also remain high for an extended period (60 days) after calving, so a waiting period after calving must be employed in order to eliminate false positives due to this situation. Blood testing is a yes or no answer and cannot be used to determine age or sex of a fetus, nor can it detect problems with the ovaries or other organs that may be preventing pregnancy. Another disadvantage to this method is that currently the blood must be sent to a laboratory for analysis, meaning several days will pass from the time the cow is in the chute to the time when her condition is diagnosed. For this reason, pregnancy blood testing likely is of more value to dairy producers than it is to beef producers, for whom it will not be convenient to identify and sort off open cows after the test results come back. Costs of these tests vary but, for example, the lab fee for pregnancy blood testing is $4 per sample.
In many states, but not South Dakota, pregnancy diagnosis is considered the practice of veterinary medicine and cannot be legally performed by laypeople, except for owners of the cattle or their employees. However, even in states such as South Dakota, these procedures are best carried out by veterinarians. Their experience and knowledge of anatomy and pathology means that they are in the best position to not only diagnose pregnancy, but also to accurately determine physical problems within the animal.