Pregnancy Diagnosis

NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare. Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

NADIS Cattle Disease Focus – August 2005

Pregnancy diagnosis is one of the commonest tasks undertaken by NADIS vets. Proper planning of pregnancy diagnosis is an essential part of any beef or dairy enterprise. In order to do this it is important to understand how the different methods of pregnancy diagnosis work and how they can be used.

Progesterone testing
The pregnant cow has high progesterone while a cow on heat has low progesterone. Testing progesterone can thus be used as a pregnancy test. Blood or milk can be used, however milk progesterone is the most commonly used as its an easy sample to obtain, thus progesterone testing is most commonly used in dairy cows.

Progesterone testing is best used to identify cows that are not pregnant as cows, which are not pregnant, but are in the middle of their cycle will have progesterone levels as high as pregnant cows. Thus to use progesterone tests you need some data about when a cow was served and then do a test at the time when you expect the cow to be coming back into heat again.

If the progesterone is low, the cow is not pregnant and should be served again, if it is high the cow should be retested two days later. If it’s not low at this point then the cow is probably pregnant but this should be confirmed with a later veterinary pregnancy test.

Two sorts of progesterone test are available; a lab test which measures actual progesterone levels and a cow-side test which just produces a low or a high progesterone reading. Both will accurately predict non-pregnancy around 21 days post service.

Progesterone testing is also useful in identifying whether cows are cycling before they are served and thus can identify problems such as high numbers of cows not cycling. Routine use of progesterone testing would be of considerable value on most dairy farms; however, until progesterone testing becomes available in-line in the parlour, it is likely to remain an under-used test. 

Manual diagnosis
Rectal examinations have been a major part of a vet’s skills for along time and manual diagnosis of pregnancy is a tried and trusted technique. It is  relatively quick, cost effective and safe. It can be used reliably from around 6 weeks after service. The age of the calf can be determined by hand (to ±1week in the early stages) but not the sex. Depending on the set-up rates of 60-100 cattle per hour can be achieved without compromising accuracy.

The vet is looking for a positive sign of pregnancy, usually fluid in the uterus and/or the buttons of the placenta. For empty cows the diagnosis is made on the absence of those signs. For this reason a manual vet pregnancy diagnosis is more accurate in determining the presence of pregnancy than its absence.

Ultrasound diagnosis
This has been the major development in cattle pregnancy diagnosis in the last twenty years. Using rectal ultrasound allows more accurate aging, sexing (between 55-75 days pregnant) and identification of twins. It can also provide significantly more information on why a cow is not pregnant and how its ovaries are functioning.

Ultrasound can also identify very early embryonic deaths as it can pick up a calf with no heart beat, but this will considerably slow down the process. Speed is usually similar to manual diagnosis if just a diagnosis of pregnancy is required, but with very good setups and rigid scanners, rates of over 200 cows per hour have been achieved.

Ultrasound diagnosis is more reliable at 28-42 days after service than manual diagnosis as the probe is generally better up picking the small changes at this stage than the hand. However, it is important to remember that whatever method used, the earlier the diagnosis of pregnancy the greater the possibility that the calf will be lost before calving.

In regard to cost, although the equipment is expensive because most vets with an ultrasound machine will use the equipment on a large number of cows there is usually little difference in cost between manual and ultrasound diagnosis.

In cattle only rectal scanners are of value, external scanners such as those used in sheep are far too inaccurate.

While every effort is made to ensure that the content of this forecast is accurate at the time of publication, NADIS cannot accept responsibility for errors or omissions.
All information is general and will need to be adapted in the light of individual farm circumstances in consultation with your veterinary surgeon