Pregnancy diagnosis in heifers and cows

Several methods are available to determine if a cow or heifer is pregnant.

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 foetal death.

More reliable methods for detecting early pregnancy in cattle are:

• Rectal palpation
• Hormone measurements
• Early Pregnancy-associated Protein
• Ultrasound examination

For details click on the different methods.

Comparison of early pregnancy diagnosis techniques

Table 1: Pregnancy diagnosis techniques

Technique	Early testing	+ve diagnosis accuracy	-ve diagnosis accuracy
Rectal palpation	+	+++	++++
Transrectal ultrasound	++	++++	++++
Milk progesterone	+++	++	+++
Early Conception Factor	++++	+	+

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
• uterus is flaccid
• placentomes, and sometimes the foetus, are palpable
• the median uterine artery increases in diameter and fremitus can be detected.

Table 2: Positive signs of pregnancy at rectal palpation

Stage of pregnancy	Membrane slip	Amniotic vesicle	Foetus	Placentomes	Fremitus A.uterine media
					Ipsilateral	Contralateral
30 days	+	+
45 days	+	+
60 days	+	+
75 days	+	+		+
90 days	+		+	+
105 days			+	+	+
4 months			+	+	+
5 months			+	+	+	+
6 months				+	+	+
7 months			+	+	+	+

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.

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Hormone measurements

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% in a study by Pieterse et al. (1989). 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

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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.

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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:

1. Operator proficiency and availability
2. Restraint of animals

When both factors are optimised, 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.

Characteristics of the conceptus visible via ultrasound

Table 3: Day of first detection of ultrasonographically identifiable characteristics of the bovine conceptus adapted from Curran et al. (1986)

Characteristic	First day detected
	mean	range
Embryo proper	20.3	19 to 24
Heart beat	20.9	19 to 24
Allantois	23.2	22 to 25
Spinal cors	29.1	26 to 33
Forelimb buds	29.1	28 to 31
Amnion	29.5	28 to 33
Eye orbit	30.2	29 to 33
Hindlimb buds	31.2	30 to 33
Placentomes	35.2	33 to 38
Split hooves	44.6	42 to 49
Foetal movements	44.8	42 to 50
Ribs	52.8	51 to 55

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