These are the methods in which the pregnancy is detected directly by observing the fetus. This is the most definitive and ideal method for PD if it can be used early. This method also allows checking the viability of the fetus and growth rate of the fetus from time to time. But using this method requires expertise.
In this method, the animals that have not returned to the estrus after breeding are tested by rectal examination of the uterus. Depending on the expertise of the examiner the successful determination of the pregnancy can be as early as day 30. But traditionally, PD by this method is usually done from 45-60 days.
Figure: Pregnancy diagnosis by rectal palpation in cattle and buffalo (source: http://veterinarysciencehub.com/pregnancy-diagnosis-in-cow/)
Trans-rectal real time ultrasonography uses probes through the rectum and pregnancy status of the animal may be determined as early as day 25 by fetal heartbeat and is a generally accepted “gold standard” for the viable conceptus. This method also helps in monitoring fetal growth, sex, uterine morphology and viability status of the embryo.
Development of new ultrasound technologies like Doppler ultrasound and color flow mode (CFM) helps in detailed assessment of uterus, corpus luteum, ovarian follicles, and blood flow within the tissues. Doppler ultrasonography along with CFM helps in the visualization of blood flow to the corpus luteum, an indicator of pregnancy, and detecting the non-pregnant ones by day 20.
One of the main disadvantages of the direct method of PD is that the sensitivity and specificity depends on the expertise of the examiner. Ultrasonography is also not possible in the field condition as it is an expensive instrument and for the PD animal is required to be transported to the nearest veterinary hospital which may cause undue transportation stress to the animal.
