Extension Notebook: Use of real-time ultrasonography for diagnosis and reproductive management of pigs

Ultrasound is widely used in the medical and veterinary fields for assessment of internal tissues and organs. In the commercial pig industry, ultrasound is now the preferred technology for routine pregnancy diagnosis four weeks after breeding.

Application of ultrasound has been helpful to pig producers to plan the management for sows that will farrow a litter 12 1/2 weeks later. It has also been important for identifying those females diagnosed as not pregnant so that decisions can be made for continued detection of estrus and rebreeding or to designate animals for sale.

The B or brightness mode units produce a two-dimensional image on a screen in black and white, but in reality includes a full gray scale range. The machine operates using a transducer with specialized crystals that vibrate when an electric current is applied. The vibrations emit high-frequency ultrasound waves at about 5 million cycles (MHz) per second that are far above the frequency range of human hearing (20 kHz). When contact is made with animal tissues, the ultrasound waves penetrate the body and varying amounts reflect or echo back to the transducer.

The machine technology is known as pulse-echo and emits waves 1% of the time and captures the echo 99% of the time in nanoseconds. Dense tissues such as bone reflect most waves and appear as white, while less dense appears as gray, and least dense reflects few waves and appears black. The image is produced in real-time, meaning that the image is refreshed multiple times per second.

The machines were first developed for commercial use about 30 years ago, and over time have improved portability, imaging and battery life. The machines can range in size from handheld, laptop and console. Some advancements have allowed wireless transfer between transducer and screen.

Pregnancy diagnosis is performed around 28 days after breeding females. At this stage it is very easy to perform for sows in pens or crates. The procedure is painless but does require some physical effort by the technician. There are transducer extension rods as well that can aid in transducer application to the skin.

A small amount of lubricant is applied to the transducer and then the transducer is applied to the skin of the lower abdomen of the sow, just ahead of the rear leg (see Image 1).

At this stage of pregnancy, the fluid in the placental membranes increases considerably, and can be visualized within the uterus with just a few seconds of contact (Image 2).

For nonpregnant animals at this stage, there is no visible fluid. But accuracy is never 100% and errors can occur. Training and experience can help prepare users for recognizing problems. In cases of uncertainty, decisions can be made to test again a week later.

Because not all of the females in a testing group may have been bred on the same day, it is important to make sure testing is not done too early. Just one week earlier, the visible fluid is halved and can increase uncertainty, errors and time to decide. Testing too late can also present challenges as the more dense fetal tissues increase within the fluid.

It is important for technicians to recognize poor image quality as this can greatly increase scanning time and errors. In operations with available labor, producers check for return to estrus three weeks after breeding. This is often the first sign that sows failed to conceive and can be rebred at this heat. But only about half of the nonpregnant sows return to estrus at this stage and the rest elude detection.

With the high costs of feed, energy, space and labor, it is important to control costs using information to make management decisions. Farms can troubleshoot pregnancy failures by using return to estrus, confirmation of pregnant and nonpregnant animals at four weeks using ultrasound and investigating sources of error in pregnant sows that fail to farrow a litter.

Robert V. Knox is a swine Extension specialist, University of Illinois Champaign-Urbana.