By Sandy Johnson, Extension Beef Specialist, Colby
For any number of reasons from shortage of pasture to cattle marketing opportunities, knowledge of if and when a cow or heifer is pregnant is valuable. That information can be used to identify early bred yearlings for replacements and late bred or open females to remove from pasture in order to extend the grazing season. Heifers that are known to be pregnant to an AI sire bring premiums. A group of yearling heifers pregnant with heifer calves and consequently less expected calving difficulty may be worth more than those with male calves.
Calving distribution reflects past reproductive and nutritional management. Information from staging pregnancies should mirror the calving distribution with the advantage of knowing the outcome earlier in the production cycle. If you learn in August that few cows conceived early in the breeding season there is still time to plan and execute improved nutritional management during late gestation and early lactation so cows begin to cycle earlier the next season. The cull cow market historically declines in association with common weaning times of spring calving herds. Information on pregnancy status is valuable in culling decisions. The more cows that need to be culled, the bigger the impact of timely marketing. Understanding the options available for staging pregnancies and the pros and cons of each will help determine how these tools can best be applied in different production settings.
Rectal palpation is the most commonly available tool for pregnancy determination and staging. Palpation skills vary with experience and exposure to a range of pregnancy stages. Some are comfortable with distinguishing 35 to 40-day pregnancies and may get routine exposure to that stage of pregnancy at a dairy. In areas with a shortage of large animal veterinarians, obtaining the service may be difficult. As the pregnant uterus drops over the pelvic rim, the accuracy of staging decreases. The most detailed information from staging via palpation would come when pregnancies are under 100 days. Estimates on stage of pregnancy made past this point are less specific, often indicating a trimester and not months or days of pregnancy, yet still valuable.
More and more bovine practitioners can offer ultrasound with their services. As with many technologies, machine cost has come down and consequently use has expanded. While embryos can be identified as early as 25 to 28 days of age, more skill and time is required. When larger groups of females are scanned, 30 days makes a more practical lower limit. Ultrasound allows a fetal heart beat to be observed so there is no question of viability on that day. A twin pregnancy could also be detected. Fetal sexing requires additional experience with ultrasound to attain a professional level of accuracy. The earliest time to fetal sex is around 55 days but due to variation in development, a time period of 60 to 100 days is generally targeted. In some cases, gender can be identified up to 120 days, for example in a relatively small heifer with the fetus positioned just right.
Commercial blood tests are also available to determine pregnancy status. The tests detect one of a number of pregnancy specific proteins produced by the placenta. Thus, depending on which protein and test provider, earliest detection date varies from 28 to 30 days of gestation and proteins remain in the system from 73 to 90 days after calving. When first released, the tests were only conducted in commercial labs. Now a home version is available but the assay requires at least 21 minutes to get results. Efforts are underway on a chute-side version but nothing has reached the market yet. A disadvantage of the blood test is that the proteins remain in the system after fetal loss occurs, and so a positive test indicates the female is or was pregnant. Pregnancies can be roughly staged with blood pregnancy tests if they are repeated for two or more cycles.
Some embryonic and fetal loss occurs normally, most before day 30, but some cows pregnant at 30 days will not be pregnant at 60 days after mating. To some this might seem like the pregnancy check “caused” the loss. If low stress handling and good palpation skills are practiced, the loss is most likely due to something other than the testing process. This does mean pregnancy tests performed relatively early may need to be repeated. Even so, fetal loss from 1 to 2% from the second trimester to term is considered normal.
Costs will vary with numbers and providers but for yes/no information a blood test and ultrasound costs may be fairly close. Your local veterinarian can discuss the timing and options that best fit your production situation and goals. Stage of pregnancy can be very valuable information when making decisions related to drought management, adjusting winter feeding plans and trying to take advantage of market opportunities. Arguments have been made to wait until calving time to determine pregnancy status or when pregnancies are well into the second and third trimester as this has “worked” in the past. We have seen many things in our lives that are a departure from ‘normal’ this year. Your business will be in a better position to adapt to variation in weather and markets with detailed information on pregnancy status and stage.
