Bovine Pregnancy diagnosis

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Bovine Pregnancy diagnosis IVSA Standing Committee on Veterinary Education (SCoVE)

Attributes of the ideal pregnancy test An ideal early pregnancy test for

dairy cattle would be • Sensitive (i.e. correctly identify pregnant animals) • Specific (i.e., correctly identify non-pregnant animals) • Inexpensive • Simple to conduct under field conditions • Able to determine pregnancy status at the time the test is performed Most direct and indirect methods for pregnancy diagnosis exhibit one or more of these attributes, but none currently available or under development exhibit all of them.

Pregnancy diagnosis Early identification of pregnancy improves reproductive efficiency and pregnancy rate in cattle by decreasing the interval between calvings. That is usually recommended to remain around one year.

If oestrus signs are not observed around 3 weeks after service or insemination, the cow is generally assumed to be pregnant.

Indirect pregnancy finding is also corpus luteum three weeks after service. Still not all of those cows are pregnant, and on the other hand, up to 7% of pregnant cows will show some signs of oestrus during pregnancy. Therefore, more accurate diagnosing methods has been implemented.

There are four techniques of diagnosing pregnancy Direct: • rectal palpation • ultrasonography Indirect: • hormone measurements • pregnancy associated proteins

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Rectal palpation There are two different methods of pregnancy diagnosis by rectal palpation, depending of the stage of the pregnancy. Routine palpations are made at week 8 and more of pregnancy, and earlier than that it is called early pregnancy detection. Key point doing early detection by palpation is turning uterine horns upside down, and palpating them carefully through. Pregnancy aged less than 8 weeks can still fit to horns under the body of uterus and that’s why turning the uterus is required.

Palpation of the uterine contents rectally is the oldest and the most widely and commonly used method for pregnancy diagnosis. It is fast, relatively cheap and accurate. Pregnancy diagnosis after insemination can be conducted as early as 30 days and even less, with experienced and trained palpator. In that case it doesn’t make big difference in timing to the pregnancy diagnosis made with ultrasonography (usually made from the gestation day 26)

Pregnancy findings Early pregnancy diagnosis (4-8 weeks) Based on a combination of the following: •

Asymmetry of the uterine horns

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Decrease in the tone of the pregnant horn

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Fluctuant contents in the pregnant horn (later both horns)

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A palpable corpus luteum on the ovary on the same side as the pregnant horn

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Membrane slip

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Appreciation of an amniotic vesicle

Safety

Diagnosis in later pregnancy (>2 months) •

Cervix is located anterior to the pelvic rim and the uterus cannot be retracted

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Uterus is flaccid

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Placentomes, and sometimes the foetus, is palpable

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The median uterine artery increases in diameter and fremitus can be detected

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Some studies have suggested that transrectal palpation as a early pregnancy detection method increases the risk of iatrogenic embryonic mortality. Rectal palpation is considered a safe method for pregnancy diagnosis in cattle.

Nonetheless early or inappropriate palpation of the amniotic vesicle may damage the embryo and cause embryonic mortality. Therefore membrane slip (slipping the fetal membranes while taking them between thumb and index finger) is also recommended to do only if expecting pyometra.

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JUNE 2016

Ultrasonography

Ultrasound of a 25-day-old fetus [Sijoita lähde tähän.]

A probe is inserted through the rectum and positioned above the uterus and slipped on the surface of the both horns. Different proportions of the sound waves emitted are reflected back to the probe, depending on the density of the tissue. Fluid, such as blood or follicular fluids, does not reflect sound waves and no image (black) appears on the screen.

Bone is the densest tissue and reflects sound waves almost completely depicting white images.

In the 1980s, real time ultrasonography was developed for use in domestic animals. Real time (B-mode) ultrasound is a reliable and relatively simple method of diagnosing pregnancy with high accuracy as early as day 26 although presence and vitality of the embryo can be confirmed by the detection of a heartbeat as early as 19 to 24 days of gestation. Due to shape of the bovine uterus, performing pregnancy diagnosis with ultrasonography needs some practice!

Additional information gathered using ultrasonography that may be useful for Abdomen reproductive management include evaluation of ovarian structures; identification of cows carrying twin fetuses, and determination of fetal sex.

Safety Cows diagnosed pregnant at an early ultrasound exam have a greater risk of early embryonic loss due to natural early embryonic loss. Therefore, they must undergo subsequent pregnancy examinations to identify and rebreed cows that experience such loss.

Although the rate of pregnancy loss is significant in studies using ultrasound to assess the rate of loss, the technique itself has not yet been implicated as a direct cause of embryonic mortality in cattle.

Ultrasound of 50-day-old fetus

Disadvantages

The main disadvantages of the use of ultrasonography are related to cost and time involved with the use of this technique. Ultrasound machines are relatively expensive and it takes more time to perform a pregnancy diagnosis with an ultrasound machine than by rectal palpation. Also the training of the operator needed to interpret the images also can serve as a disadvantage. How ever, if current trends continue, transrectal ultrasonography may displace transrectal palpation as the direct method of choice for pregnancy diagnosis among bovine practitioners.

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Indirect pregnancy diagnostic methods Indirect methods for early pregnancy diagnosis use qualitative or quantitative measures of reproductive hormones at specific stages after AI or detect conceptus specific substances in maternal body fluids as indirect indicators of the presence of a viable pregnancy.

Research to develop commercial indirect methods for pregnancy diagnosis continues because these methods are non-invasive and the tests can be marketed to and performed by dairy farmers or herd employees. Currently available methods or methods under development for indirect diagnosis of pregnancy include measurement of endocrine hormones such as progesterone, and pregnancy specific proteins such as pregnancy-associated glycoproteins or the early pregnancy factor.

Progesterone assay The progesterone secreted by a functional corpus luteum between 18 and 24 days after service or insemination is an early indication of pregnancy. It can be assayed in milk or plasma. To use the milk progesterone test as a pregnancy indicator the milk sample must be collected between 21 to 24 days (closer to day 24) after the cow was in estrus and inseminated. This eliminates the possibility of long oestrus intervals, which might result in false positives.

Low progesterone would indicate that the cow is not pregnant and high progesterone would indicate that the cow has a functional corpus luteum and might be pregnant. Therefore, the test is most accurate in determining that a cow is not pregnant, because if the progesterone levels are low she cannot be pregnant.

Numerous studies indicate that the accuracy of early pregnancy diagnosis by milk progesterone is only about 80%. Reasons for this can be variation in estrus cycle length between cows, estrus detection errors, uterine disease (pyometra), ovarian dysfunction (luteal or follicular cysts), and early embryonic mortality reliability of milk progesterone for the diagnosis of pregnancy is not satisfactory in it and should be confirmed by palpation or ultrasound.

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Pregnancy associated proteins Proteins produced and secreted specifically by the placenta early during pregnancy are obvious candidates for development of an early pregnancy test. However, the proteins produced by the placenta vary widely among mammals. For example, only the higher primates produce a chorionic gonadotropin (CG) homologous to the human protein (hCG) required for luteal support early during pregnancy, whereas only ruminant ungulates are known to produce type I interferon as an antiluteolytic hormone. As cattle do not produce a chorionic gonadotropin, the placental hormone that modern rapid pregnancy tests for women are based upon, research has focused on discovery and characterization of pregnancyspecific proteins suitable for determining pregnancy status in cattle early post breeding.

Recently available tests detect so-called early conception factor (ECF) or pregnancy-associated glycoprotein in blood samples. Early Conception Factor (ECF) test reportedly detects a pregnancyassociated glycoprotein within 48 hours of conception Because of the high incidence of embryonic mortality this test should be treated solely as an indication of conception. Pregnancy should be confirmed later by rectal or ultrasound examination

IVSA SCOVE

JUNE 2016