Farm Animals Pregnancy Diagnosis
Farm animals pregnancy diagnosis requires a multifaceted approach, which you will discover in the course of this article. Successful pregnancy and subsequent delivery is crucial for any profitable livestock farming.
Farm Animals Pregnancy Diagnosis
The diagnosis of pregnancy requires a multifaceted approach using 3 main diagnostic tools. These are history and physical examination laboratory evaluation, and ultrasonography.
Visual methods are far from perfect in domestic animals. In animals like cattle, buffaloes and mares‟ recto genital palpation and trans-rectal ultrasonography continue to be the methods of choice for an accurate and early pregnancy diagnosis.
In sheep, goat, sow, bitch and cat ultrasonography is the only reliable method of pregnancy diagnosis. In the camel, cocking of the tail is an effective visual method of pregnancy diagnosis and recto genital and ultrasonography are also useful. In rabbits, palpation of the abdomen in pregnant does has maize grains like feeling by mid gestation period.
Visual Methods of Farm Animals Pregnancy Diagnosis
Non Return to Oestrus
When an animal is mated or inseminated and it does not return to oestrus, the owner usually thinks that the animal has become pregnant.
However, many a times the animal does not return to oestrus because of non-regression of CL due to reasons other than pregnancy.
Cocking of the Tail
The pregnant female dromedary camels exhibit a characteristic behavior when approached by a male or a person.
The female assumes a stiffened posture with the head held high and tail curled upwards. This is known as cocking of the tail.
This behavior appears 14 to 15 days after fertile mating and known to be 95% reliable for pregnancy diagnosis in quiet and calm dromedary female camels. However, many false positives can be obtained in agitated females if the observer is untrained.
Tail cocking is also observed in the pregnant bactenian camel although not with the same intensity as in the dromedary female camel.
Clinical Methods of Pregnancy Diagnosis
Four clinical methods are available for farm and pet animal species.
- Rectal Palpation
- Abdominal ballottement
- Ultrasonography
- Radiography
1. Rectal Palpation
Transrectal palpation is the oldest and most widely used method for early pregnancy diagnosis in dairy cattle.
In most large domestic animal species like cattle, buffaloes, mares and female camels, recto-genital palpation (with some limitation) is the easiest, cheapest and fastest method of pregnancy diagnosis with little or nil harm to the animal and its fetus when performed carefully.
To a limited extent, this method is used for pregnancy diagnosis in pigs.
Precautions during Rectal Palpation
Ruthless movements of the hand in the rectum should be avoided.
Examiners must trim nails and avoid using dirty soiled sleeves.
Rectal examination without sleeve must be avoided especially in mares to avoid contracting diseases and obnoxious odors.
Rectal examination of animals suffering from severe should be extremely gentle or better avoided as the blood vessels are more fragile and bleed easily.
Compared to cattle, rectal palpation in buffaloes must be gentle as the rectal mucosa is more fragile and bleed easily.
Uncareful palpation of the uterine horns with undue pressure can cause rupture of the amniotic vesicle and loss of an early pregnancy and hence this must be avoided.
2. Abdominal Ballottement
This involves palpation to determine pregnancy by pushing up against the uterus with the finger so as to feel any downward pressure exerted by an embryo as it sinks back into place in the amniotic fluid. In cows this can be done at 7m and more
3. Ultrasonography
Ultrasonography is a high frequency sound wave. Ultrasonography has gained popularity in veterinary medicine and some reproductive physiology and has become the method of choice for diagnostic imaging of the various organs of the body, including reproductive organs.
The ultrasound equipment basically consists of a transducer and a scan converter. The transducer is the ultrasound producing part. The ultrasound is transmitted to the patient from the transducer and propagates through the tissues.
Trained personnel are needed to interpret the variations in brightness displayed. Different instruments are used in ultrasonography.
Sonographic Findings during Pregnancy
Interpretation of sonograms of the reproductive tract requires an understanding of the composition of the images and an awareness of the possible artifacts which can occur and lead to misdiagnosis.
4. Radiography
To a limited extent, radiography has been used for pregnancy diagnosis in the small ruminants (sheep and goat), the companion animals (dog and cat) and rarely in pigs.
The technique is known to be good in evaluating fetal numbers in the bitch and cat, but is poor in evaluating fetal viability. It uses X-rays, therefore risky to the fetus, needs expertise and is costly.
Others Include:
Fetal Echocardiography
To a limited extent, fetal echocardiography has been used in the past to diagnose in cattle, sheep and mares, but with the advent of ultrasonography its use has been limited.
Vaginal Electrical Resistance
The conductivity of the vaginal mucous membrane changes at oestrus due to increased hydration increased blood supply and other changes. When measured by ohm meters, the vaginal electric resistance (VER) is low at oestrus.
Hence when VER is measured constantly, animals returning to oestrus can be identified and thus those probably becoming pregnant can be differentiated but mistakes are common.
Laparoscopy
Laparoscopy can be used as a method of pregnancy diagnosis by directly visualizing the genitalia in animals however, the invasive nature of the technique, the high cost of equipment and clinic required, and the availability of non-invasive techniques limits the use of this technique as a means of pregnancy diagnosis in most animals.
Laboratory Tests for Pregnancy Diagnosis
The various laboratory tests developed for pregnancy diagnosis in domestic animals are indirect methods of pregnancy evaluation and utilize qualitative or quantitative measures of reproductive hormones at specific stages after AI or mating or detect conceptus specific substances in maternal body parts or body fluid as indirect indicators of the presence of a viable pregnancy.
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Unfortunately, none of the methods developed so far in animals are as accurate as is the detection of hCG in pregnant human females.
However, the research to develop commercial indirect methods continues because these methods are non-evasive and the tests can be marketed to and performed by dairy farmers. The currently available methods are briefly described.
Progesterone Hormone Assay
The corpus luteum formed on the ovary subsequent to ovulation produces progesterone for maintenance of pregnancy for a reasonable period in some species and for entire gestation in the species like the cow, buffalo, goat and sow. The elevated progesterone levels are used as means of pregnancy diagnosis.
Estrone Sulfate
The estrone sulfate is produced by the fetomaternal axis or the conceptus and therefore its presence in urine, milk, feces or blood is an indicator of pregnancy. The detection of these hormones depends on availability of appropriate kits and personnel.
Chemical Tests for Pregnancy Diagnosis
Most chemical tests reported in the past appear to be of historic importance only in current day pregnancy diagnostic procedures. Some of the chemical tests that utilize urinary estrogens or other molecules as a basis of pregnancy diagnosis in domestic animals are described below:
1. Cuboni Test
This test was first developed by cuboni (1934) and modified later (Galina and COX, 1969). The test is performed in the mare for detection of pregnancy through assay of urinary conjugated estrogens.
The cuboni test is only effective beyond 150 days of gestation, and also predicts fetal viability.
2. The Mouse Test
In the mouse test, the serum or urine from pregnant mares when injected to ovariectomized mouse or rats would induce vaginal edema, appearance of cornified cells and mucus discharge due to presence of estrogens in the pregnant mare’s serum or urine.
There are many other tests available.
Some other previously described tests for pregnancy diagnosis in cows include two tests on milk:
(1) Milk alcohol coagulation test: In this test, there is coagulation of milk from pregnant cows when mixed with equal quantities of alcohol and allowed to stand for 1-3 hours.
(2) Copper Sulfate test: 1ml of milk when mixed with a few drops of 3% copper sulfate coagulates if the animal is pregnant.
3. Kosjakov’s Test
This test apprehends that the sulfur content of hair in pregnant animals is increased. A few other tests exist.
4. Assay of Gonadotrophins
The human female secretes the gonadotropin hCG which is present in sufficient quantities in the urine of pregnant women and many simplified tests have been developed to detect this molecule in urine for an easy pregnancy diagnosis in women.
The eCG continues to be secreted from day 40 to 120 days of pregnancy and is the basis of tests currently available on farm.
Biologic Tests
Several biologic tests were developed for the detection of eCG including the AschiemZondek Test, the Friedman test (rabbit test) or the frog or toad test.
In Aschiem Zondek test – A woman’s urine is injected into an immature rat or mouse. If the subject was not pregnant, there would be no reaction.
In the case of pregnancy, the rat would show an oestrous reaction (be in heat) despite its immaturity. This test implied that during pregnancy there was an increased production of the hormone.
Friedman Rabbit Test
Serum from test mare is injected (2ml given IV) to rabbits (14 to 20 weeks of age) kept in isolation and laparotomy performed 24 hours later. A positive test is indicated by the presence of corpus haemorrhagicum and uterine edema.
Toad Test – The basis of this test is the concept that the sperm cells are emitted by toads/frogs only when stimulated with female frogs or gonadotrophins.
Many of the above older methods have now been replaced by newer methods including radioimmuno assay, radioreceptor assay, haemagglutination inhibition test, ELISA and indirect latex agglutination tests. Commercially available kits are in use at many places for these assays.
Pregnamare (R) is one such test, which can be performed on blood between day 40 and 100 of pregnancy, however, false results may be obtained if fetal death occurs after formation of the endometrial cups.
Other Methods
Cervical Mucus
Some years ago, a pregnancy diagnosis based in determining differences in cervical mucus using nuclear magnetic resonance was used (Merilan,1983). The test looked promising at that time but no subsequent information is available.
Milk Ejection by Low Dose Prostaglandin
This is a method tested some years ago involving the injection of low does breeding resulting into milk ejection.
The animals detected further as pregnant showed an increase in the pressure in the milk ejection and alveolar milk volume collected by a test probe in comparison with the non-pregnant cows.
However, due to potential dangers of inducing lubeolysis by accidental over dosage, the use of this technique of pregnancy diagnosis, could not gain wide popularity.
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Pregnancy Associated Glycoprotein (PAG)
Pregnancy specific proteins are known to be produced in various ruminant species including cattle, buffalo, sheep and goats. Recently too, the existence of PAG has been documented in bovine milk.
Early Pregnancy Factor (EPF)
This protein molecule was first identified in pregnant mice and later in sheep and cattle by using the rosette inhibition bioassay.
Relaxin Assay
Relaxin can be determined in the peripheral circulation of pregnant bitches at 20-30 days of gestation, whereas it is absent in non-pregnant bitches at all stages of the reproductive cycle.
Vaginal Biopsy
Historical assessment of the number of layers of the stratified squamous epithelium of the vaginal mucosa obtained by biopsy can be used as a method of diagnosing pregnancy in the sow.
The basis for the test is the decrease in the layers of stratum germinativum (vaginal epithelium cells: 3 to 4 layers at 18 – 25 days of pregnancy) under the unfluence of progesterone (P4).
The number of layers is high at oestrus (around 20 layers) due to influence of oestrogen hormones. It is also done in sheep after 40 days of pregnancy.
With the availability of more precise techniques of pregnancy diagnosis in sheep and sow, the use of vaginal biopsy for pregnancy diagnosis has been reduced.
In summary, detection of pregnancy on animals that have successfully conceived is part of good management practices to reduce cost and enhance productivity. Each farmer should be able to employ some of the methods of pregnancy diagnosis explained in this article.
Pregnancy diagnosis tools have been shown in this unit. The various methods are such that a good farm manager should be able to employ some to his own benefits.
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