Getting Timing Right with Pregnancy Diagnosis in Dairy Herds
The importance of a timely pregnancy diagnosis (PD) in dairy cows is widely recognised. With conception rates regularly below 50%, it is important to recognise non-pregnant cows as early as possible in order to submit animals for re-insemination and, if necessary, veterinary treatment to achieve a pregnancy within the desired period(1).
There are various methods for detecting pregnancy in cows and these include; Palpation, Ultra sound, hormonal profiles and chemical pregnancy testing.
While PD-techniques based on hormonal profiles (progesterone) are long established; alternatives to this have been developed in recent years. It is important to differentiate between the tests based on progesterone (P4) and pregnancy-associated glycoproteins (PAG).
P4-tests are widely used and available in different forms to be used on blood or milk samples, in the CIS Laboratory in Telford or on farm by the dairy team. The principle of P4-tests is to assess whether from day 18 to day 24 of the oestrus cycle P4 is present or not. The absence of P4 would then make a negative diagnosis. It is to be remembered that there is considerable variation on oestrus length. P4-tests are therefore reliable when it comes to PD-negative diagnosis (accuracy around 95%), but hardly so when it comes to diagnosing pregnant animals (around 75%). Repeated measurements or conventional techniques have to be used when it comes to confirming the finding.
Tests based on the identification of PAGs have been introduced in recent years and can be used on blood or milk. While the P4-tests are indirect in character, the PAG-based tests are in contrast specific to pregnancy. PAG tests base their diagnosis on the presence or absence of specific glycoproteins that are found only when the animal has conceived. PAGs can be detected from day 22 of pregnancy onwards and enter the bloodstream and consequently the milk. Their maximum concentration is reached from day 35 onwards. Unlike P4-tests, results from PAG-tests do not need any interpretation. The PAG-based tests allow for accurate diagnoses from day 28 onwards, providing an accuracy of >94.4% for identifying non-pregnant cows and >98.7% for pregnant ones.
In summary, PAG-based pregnancy tests must not be confused with progesterone testing. Progesterone is a hormone that occurs with peaks and valleys during the normal reproductive cycle and is not pregnancy specific. The specific nature of PAGs means that they provide a highly accurate means of pregnancy testing in cattle.
The CIS PregCheck service is non-invasive and hassle free by testing samples from milk recording. The milk pregnancy test is based on Elisa technology and detects presence of Pregnancy Associated Glycoproteins (PAGs) in the milk sample. It has a 98% level of accuracy. Contact CIS on 01923 695319 for information on PregCheck and a quotation.
1Kleen, J.L. New aspects of pregnancy diagnosis, IDEXX Publication (09-69478-00);
11 September 2019