GILLETTE, Wyo. (AP)--Larry Smith watches quietly as Dr. Marshall Kohr gives Smith's replacement heifers a good once-over.

The 230 heifers are just a portion of the 1,200 cattle Smith manages for his father-in-law, Jim Daly of Daly Livestock. Smith wants to make sure the pregnant cattle are in good shape for the upcoming calving season.

Kohr is literally up to his elbows in bovine uterus and performs a service that would, without a doubt, qualify for the new Discovery Channel series, "Dirty Jobs."

Kohr can make quick work of the physicals by using a hydraulic catch chute. It allows him to check an average of one heifer per minute.

With the help of Smith's son, hired hands and a veterinary technician, the big, leather-clad girls are herded into more manageable groups.

Cows that will calve early, late or not at all are separated from those that are on schedule to calve in late spring.

But Kohr isn't just palpating the heifers, he's peering into the small screen of an ultrasound unit tucked inside a feces-covered cardboard box. It's a far cry from the pristine hospital environment a pregnant human would encounter.

The technology that lets doctors date, sex type and check human fetuses for abnormalities is also of great use to veterinarians for use on animals of all shapes and sizes.

This is only the second year Smith has asked Kohr to use the equipment to check his cattle, but he believes the extra time and money are worth the benefits.

"I have cut down on really late cows," Smith said. "I pay for the machine, but it's worth it."

In addition to culling late cows, Smith can also take an open cow, or those without a calf, to market. Cows or heifers that have a narrow birthing canal and are more prone to birth complications can also be cut from the herd to help ease calving.

When checking cattle for pregnancy, Kohr inserts the probe into the uterus to check for a placenta, fetal parts or membranes, all of which are only present during pregnancy.

After 11 years, he has it down to a science. All 230 of Smith's replacements were evaluated in less than four hours.

Kohr can accurately date the duration of the pregnancy and determine the size of the fetus. The information helps the herd manager when it's time to separate the cattle into groups according to stage of pregnancy. It also lets him know when a heifer may need assistance during its first calving experience.

In the livestock world, ultrasound first gained popularity for use with horses, Kohr said. He gave credit to the Colorado State University Reproductive Center for spurring the use in mares in the early 1980s. But the technology has been used in beef and dairy research systems for many years. It has recently been made available to commercial livestock agriculture.

Some veterinarians will no longer rely on hand palpating alone, Kohr said. But the procedure costs twice as much with the machine. He encourages his clients to use ultrasound only if their operation would benefit.

"It depends on what their needs are," he said. "For some its definitely worth it. Sometimes you don't really need it because the need just isn't there."

Animal Medical Center charges $3 per head to perform the ultrasounds.

Determining the sex of a calf before it's born is important in purebred operations, but also can be used in commercial herds.

The information allows ranchers to find buyers for their calves based on the sex before they leave the womb. This gives them the duration of the gestation period--283 days for cows--to find the highest bidder.

When used on the outside of the body, the ultrasound technology also helps researchers make breeding selections based on the amount of intramuscular fat, better known as marbling. Marbling creates prime and choice cuts of meat that produce the tasty, juicy steaks consumers prefer. This helps producers know whether the cattle they breed will produce quality beef.

Iowa State University used ultrasound as a selection tool to help it produce the 2004 top-ranked Angus cow in the nation. They used the ultrasound technology to select cattle that now lead the Angus breed in intramuscular fat.

But as advanced as the ultrasound technology is, it still isn't necessarily something new veterinarians learn in school.

"There is a learning curve involved," Kohr said. "It's an acquired skill."

Kohr invites the newer veterinarians from Animal Medical Center along to get more experience with the machine.

"It's only natural that we're all going to be doing this sooner or later," he said. "All the young vets are going to be going for it."