Pregnancy Diagnosis
if accurate records of estrus periods and breeding dates are available, the earliest indication of pregnancy in most animals is the failure to have another estrous cycle at the expected time.
Such an absence of estrus is not, however, proof of pregnancy. A nonpregnant animal may miss an estrous cycle because of failure of the corpus luteum to regress normally or some other reproductive abnormality. An animal may also have a delay of one or two estrous cycles if an initial conception is followed by inability to sustain that pregnancy.Palpation of the reproductive tract via the rectum in the mare and cow can be useful for pregnancy diagnosis and estimation of the stage of pregnancy. in the cow, the presence of a corpus luteum in an ovary and a slight enlargement of one uterine horn as compared to the other suggest an early pregnancy. At about 3 months of pregnancy in the cow, fetal membranes and caruncles become palpable, and the uterine artery on the side with the fetus is slightly larger than the vessel on the other side. Pregnancy diagnosis by rectal palpation is considered to be more difficult in the mare than in the cow, but an early diagnostic feature is a bulge in the uterus due to the development of the amniotic sac.
Ultrasonography is used to diagnose pregnancy in a variety of domestic species, including cattle, horses, sheep, goats, llamas, and swine. The earliest time for verification of pregnancy is dictated in part by the size of the gestational sac, which in turn varies among species. In general, the times vary between about 2 weeks for mares to about 5 weeks for ewes. In large animals, the ultrasound probe can be inserted rectally so that it is closer to the uterus.