Several methods are available to determine if a cow or heifer is pregnant.
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Non-return to oestrus
If oestrus signs are not observed around 3 weeks after service or insemination, the cow is generally assumed to be pregnant. However, even if oestrus detection is good, not all of these cows will be pregnant. On the other hand, up to 7% of pregnant cows will show some signs of oestrus during pregnancy. Insemination of these animals may result in embryonic or fetal death.
More reliable methods for detecting early pregnancy in cattle are:
– Rectal palpation
– Hormone measurements
– Early Pregnancy-associated Protein
– Ultrasound examination.
1. Rectal palpation;
Advantage: immediate result enabling early treatment of non-pregnant cattle.
Accuracy:
Depends on the experience of the practitioner and can reach 95%. Rectal examination is usually carried done between 35 and 65 days post-AI.
Early pregnancy diagnosis (1-3 months)
Based on a combination of the following:
-Asymmetry of the uterine horns.
-Decrease in the tone of the pregnant horn.
-Fluctuant contents in the pregnant horn (later both horns).
-A palpable corpus luteum on the ovary on the same side as the pregnant horn.
-Membrane slip.
– Appreciation of an amniotic vesicle.
Diagnosis in later pregnancy (>3 months)
– cervix is located anterior to the pelvic rim and the uterus cannot be retracted.
– the uterus is flaccid.
– placentomes, and sometimes the fetus, are palpable.
– the median uterine artery increases in diameter and fremitus can be detected. Common reasons for errors in rectal palpation
– failure to retract the uterus
– abnormal uterine contents (pyometra or mucometra)
– incorrect service dates.
Safety :
Rectal palpation is widely used and 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.
2. Hormone measurement:
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. Optimal assay time is 24 days after service or AI, this eliminates the possibility of long oestrus intervals which might result in false positives.
Accuracy
The sensitivity (i.e. accuracy in detecting pregnancy) of the cow-side milk progesterone (EIA) test was 93.1%. However, specificity (i.e. accuracy in detecting non-pregnancy) was only 39.3%. A large number of non-pregnant may thus be diagnosed as pregnant. Common reasons for errors in hormone measurements pyometra/persistent corpus luteum short oestrus intervals cystic ovarian disease (luteal cysts) incorrect handling of the samples and test kit.
3. Early pregnancy-associated protein:
Recently available tests detect so-called early conception factor (ECF) or pregnancy-associated glycoprotein in blood samples. They are reported to detect the pregnancy-associated 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.
4. Ultrasound examination:
Early identification of non-pregnant cows post-breeding improves reproductive efficiency and pregnancy rate in cattle by decreasing the interval between AI services and increasing AI service rate. Real-time (B-mode) ultrasound is a reliable and relatively simple method of diagnosing pregnancy as early as day 26.
Accuracy
An accuracy of over 99% can be achieved, enabling fertility problems to be identified rapidly.
Two factors affect the speed at which ultrasound examinations can be conducted on a dairy farm:
-Operator proficiency and availability
-Restraint of animals
When both factors are optimized, the speed of ultrasonography can approach that of rectal palpation, while exceeding palpation in the amount of information gathered from each animal.
The main advantage of scanning is that it can give an accurate diagnosis earlier than rectal palpation.
Early pregnancy diagnosis and embryonic loss:
Pregnancy can be detected earlier with ultrasound compared with rectal palpation. The rate of detection of early embryonic loss is thus also higher.
10 to 16% of cows diagnosed pregnant at 28 days post-AI, experience early embryonic loss by 56 days post-AI.
Cows diagnosed pregnant at 28 days post AI using ultrasound should be scheduled for a subsequent examination around 60 days post-AI when the rate of embryonic loss per day decreases dramatically.