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ULTRASOUND USED TO IMPROVE REPRODUCTIVE MANAGEMENT

by: W.E. Beal
Ph.D

An ultrasound machine is a powerful tool that allows a veterinarian or rancher to essentially “climb inside the cow” to look at the ovaries and uterus.

During an examination an ultrasound transducer is passed into the rectum of a cow and placed over the reproductive tract. The ultrasound machine displays a black and white image of the ovary or uterus. Ultrasound reveals far more detail than can be gained by traditional rectal palpation. The most practical uses of ultrasound in reproductive management of beef cows are for pregnancy diagnosis and fetal sex determination.

Early Pregnancy Diagnosis

Ultrasound pregnancy diagnosis has been reported to be 100 percent accurate by 20 days after breeding. In “real life” however, it is more practical to wait until day 25 to 30 of pregnancy to detect an embryo. By that time the embryo is a little larger and more easily spotted on the ultrasound screen. The efficiency (speed with accuracy) of detecting early pregnancy with ultrasound is markedly increased when the embryo can be detected more easily. Therefore, when scanning large numbers of cattle, it is more practical to scan cows that are at least 26 days pregnant.

Pregnancy detection with ultrasound offers several advantages over rectal palpation when used 20 to 100 days after breeding. In addition to allowing earlier detection of pregnancy, fetal aging during that period to predict calving date can be more precise if fetal body parts are measured on the ultrasound screen rather than estimated by hand. Reducing the handling of the pregnant tract by using ultrasound rather than palpation should also reduce the risk of inducing embryonic death when searching for early (< 45-day) pregnancies. After 100 days into pregnancy the fetus has usually descended too far into the cow to be reached with the ultrasound transducer via the rectum, therefore, many of the advantages of ultrasound over rectal palpation by hand are lost after that time.

Accurate early pregnancy diagnosis is valuable in an A.I. breeding program because it can be used to verify early breeding and enable movement of pregnant cows out of confinement, thereby decreasing feed costs. For example, in one large purebred herd on the Oklahoma/Kansas border 1,800 cows are gathered off wheat pastures and confined in pens on Oct. 1 to begin the breeding season.

In the breeding pens the cows are fed harvested feed and supplement. Between 25 and 35 days after A.I. breeding each cow is pregnancy checked with ultrasound, and pregnant cows are quickly moved out of the pens and back onto wheat pasture to reduce feed costs. This ranch paid for a new ultrasound machine with the savings on feed cost after one month.

Ultrasonography offers the unique opportunity of determining if an embryo is alive by viewing the heartbeat of the embryo during pregnancy diagnosis. We have studied embryo loss in beef cows on several ranches. We found that from 25 and 65 days after breeding 4 to 8 percent of the cows that were pregnant lost an embryo. Hence, although early pregnancy diagnosis with ultrasound is possible and has advantages, re-checking pregnancy at 90 days or later is advisable. At the ranch described above cows turned out on wheat pasture were still observed once a day to pick up any heats that occurred due to embryo loss, and they were re-checked by palpation before the calving season started.

If a cow is examined with ultrasound and observed to have a dead embryo in her uterus (no heartbeat) at 25 to 65 days after breeding, we have found that treatment with a drug (e.g., Lutalyse, Prostamate or Estrumate) to regress the corpus luteum and expel the dead embryo is followed by a heat two to seven days later.

Surprisingly, breeding at that heat has been more successful (50 percent preg rate) than we expected. Hence, detection of a dead embryo with ultrasound that might be missed by rectal palpation can be followed quickly by a return to pregnancy if the animal is treated and rebred.

Fetal Sex Determination

One of the most talked about uses of ultrasound technology is for determining the sex of a fetus at 60 to 80 days of pregnancy. Most often this information is used to merchandise cows or heifers more effectively. A cow sold with a heifer calf at side and known to be pregnant carrying another heifer would be a great deal for a buyer looking to build a cowherd. Conversely, pregnant commercial heifers carrying bulls would be a way to maximize return on the investment when every heifer has a steer calf at weaning next year. Either way, the buyer who knows more about the product he is purchasing usually feels more secure about his decision to purchase.

Male and female fetuses can be identified beginning 55 days after breeding by looking for the penis and scrotum on the males and the absence of those structures along with a vulva on the females. The accuracy of fetal sexing is high (> 99 percent) when the procedure is optimized by proper timing. Sex determination prior to 60 days is more difficult because the size of the genital structures is small. Therefore, determining the sex becomes easier as the fetus gets older.

However, the longer the cow is pregnant the greater the chance that the pregnant uterus will descend into the abdominal cavity which makes sexing difficult or impossible. These factors make the best “window” for fetal sexing occur between 60 and 90 days after breeding.

Cost of Ultrasound

The cost of ultrasound technology will depend on whether a ranch chooses to hire a technician or purchase an ultrasound machine for their own use.

Ultrasound units suitable for on-farm use cost between $5,000 and $12,000. Most farms don't have enough demand to justify that cost, nor do most ranchers have the desire to learn how to operate an ultrasound machine. Therefore, in most cases hiring a technician for occasional work is more sensible.

Hiring a veterinarian to pregnancy check with ultrasound instead of by rectal palpation usually increases the price of pregnancy checking by $1 to $8/head, depending on the number of animals being checked.

Like all management practices, the use of ultrasound is justifiable in some situations, but not others. Knowing and utilizing the advantages of ultrasound will make some progressive producers more successful.

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