Currently, daily boar exposure is the earliest and best means to identify open sows and gilts. Daily boar exposure usually begins around 17 or 18 days after breeding thus allowing rebreeding or culling of the open females. A dependable means to diagnose pregnancy before or at 19 to 20 days after breeding could theoretically decrease labor, since only females deemed open would be exposed to boars.

Since pregnancy may end prematurely or boar exposure does not catch all open sows and gilts in heat, producers usually monitor their animals later in pregnancy. Two types of pregnancy detection commonly used are A-mode ultrasound and Doppler. A-mode machines emit a beep in response to fluid, whereas Doppler units detect movement indicative of pregnancy (usually due to the pulsing blood flowing through the uterine artery). Both types are useful to producers but each has limitations.

The A-mode ultrasound is very accurate beginning around day 35 of gestation. However a false positive diagnosis may result if the probe is incorrectly positioned. If the transducer is oriented toward the rear where it in turn directs the sound waves through the bladder a beep will sound that suggests pregnancy. The user may then make a wrong call as the animal may or may not be pregnant. In addition, these devices are 'yes' or 'no', there is little room for judgment. On the other hand, Doppler ultrasound is used as it reduces the risk of false positives. Although the risk of false positives is reduced, problems occur when the animal is moving around, eating, drinking, or grunting. All types of body movement mask the sound of the pulsing blood.

Research is currently being conducted at North Carolina State University in the Colleges of Agriculture and Life Sciences and Veterinary Medicine to evaluate the usefulness and accuracy of real-time ultrasound for enhanced pregnancy detection. Real-time ultrasound uses the same principles of emitting and receiving sound waves by means of a transducer; however, unlike A-mode, real-time displays the information as a two-dimensional image.

The advantages of real-time ultrasound begin with the day at which pregnancy can be diagnosed accurately. Current research at NCSU with a 3.5 MHz abdominal probe suggests that pregnancy can be confirmed on day 22 after breeding. Also research is in progress using a 5.0 MHz abdominal probe with the idea that pregnancy can be detected earlier (day 19 to 20). By confirming pregnancy at or earlier than 22 days after breeding, substantial savings occur. At this time open animals that are to be culled can be removed reducing feed and housing costs considerably. Conversely, only females deemed open would be subjected to heat checking, therefore decreasing labor costs. Another important aspect of real-time ultrasound is that much of the guesswork is removed in the diagnosis. By seeing the internal structures, the operator can differentiate between the bladder and the amniotic fluid in the uterus. This should reduce the false positive diagnoses because of scanning the bladder.

Although our primary interest is in pregnancy detection around day 21-22 after breeding, we have investigated other uses of real-time ultrasound. Currently, work is underway to evaluate its usefulness in determining fetal viability. In preliminary work we have found that viability can be determined around day 35-40 after breeding as verified by fetal heartbeat or movement. By visualizing the reproductive tract and its contents, other uses may be possible. Research is underway to investigate these possibilities.

Acknowledgments: Supported by Colleges of Agriculture and Life Sciences and Veterinary Medicine, NC Agricultural Research Service, and the North Carolina Pork Producers Association.