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15. Pregnancy detection equipment using a Doppler transducer to measure changes in nature and frequency in the flow of blood is also available. The equipment is extremely simple and low cost but not always effective and has been largely superseded by the more sophisticated and accurate technique of ultrasonography. The procedure is performed per rectum and the middle uterine artery is identified by touch and then the probe is held close to the artery to record the Doppler signal. This appears as a trace on the screen and also as an audible signal. Pregnancy alters the character of blood flow to the uterus and this alteration can be detected in the audible signal and the trace. The technique requires a trained ear and knowledge of the format of the trace signal and in skilled hands it can be of use in pregnancy detection work.
16. Like real-time ultrasonography in bovines, this procedure requires rectal examination of the animals and the risks of welfare problems caused by it are no different. Lay operators should therefore be trained to adequate standards and the recommendations at paragraphs 11-14 should apply.