Dairy Pipeline: November 2005
John F. Currin Extension Dairy Veterinarian (540) 231-5838 email: firstname.lastname@example.org
Pregnancy diagnosis is an important part of the reproductive program on most dairies. Finding open cows is the most important aspect of pregnancy diagnosis. Cows that are pregnant do not need further reproductive attention. It is the open cow that needs semen as soon as possible. Many veterinarians are starting to employ ultrasound in an effort to detect pregnancy at earlier dates than are possible by rectal palpation. Pregnancies as early as 25-30 days can be detected by ultrasound. The earliest time that pregnancy can be detected depends on a variety of factors such as ambient light and operator experience. If there is bright sunlight where ultrasound is being performed it can make detection of very early pregnancy more difficult. The primary advantage to early pregnancy diagnosis is the ability to find open cows quicker and get those cows enrolled back into the current farm system for getting semen into cows. The poorer the heat detection is on the farm the more important it is to consider early pregnancy diagnosis. The time interval between herd health visits also affects the advantages of early pregnancy diagnosis.
If your current cut-off for palpation is 35 days bred and a cow in your herd is 34 days bred (but open) when the veterinarian visits and the veterinarian comes every 4 weeks that cow will be 62 days bred when the veterinarian discovers that she is open at the next visit. If heat detection is a challenge on your farm as it is on many Virginia farms there is a good chance you may not find this cow in heat and therefore she will not have had another opportunity to get inseminated and become pregnant.
One important consideration in early pregnancy diagnosis is the increased likelihood of cows losing early pregnancies (See figure 1). The higher percentage of pregnancy loss is not a reflection of the abilities of the veterinarian doing pregnancy diagnosis or an indication of infectious disease but rather of natural death loss. Some farmers reconfirm pregnancies in cows already diagnosed pregnant. If you choose to use early pregnancy detection it is very important to recheck pregnancies particularly in those cows less than 40 days bred at pregnancy diagnosis. It is important for producers to understand that a higher percentage of cows will return to heat after being diagnosed pregnant than when pregnancy was diagnosed further along in the pregnancy.
Traditional pregnancy determination methods have served producers well for many years and continue to do so today. Early pregnancy diagnosis by ultrasound is another tool you may want to discuss with your veterinarian to see if it is right for your farm. Hopefully this article will give you insight into the advantages and limitations to early pregnancy diagnosis to discuss with your veterinarian.
Figure 1. Pregnancy losses from 28 days post AI to calving in lactating dairy cows. Pregnancy status was diagnosed using ultrasound at 28, 42, 56, 70, and 98 days post AI, and calving data were recorded at parturition. The conception rate at 28 days was 32%. Data adapted from Vasconcelos et al., 1