Pregnancy testing

Each farm needs a strategy to identify and record which cows are pregnant and when they conceived. Several strategies are available. The best strategy for your herd will depend on what information you require from pregnancy testing.

For effective management decisions, it is essential to know which cows are pregnant and when they conceived, as this determines when they will calve. This allows you to:

• accurately measure the 6-week in-calf rate to assess overall herd reproductive performance
• confidently cull cows as empty, at the right time
• confidently dry-off cows at your preferred time before their due-to calve date
• differentiate AB from natural mating pregnancies
• identify cows due to calve late
• more accurately select cows that are close to calving
• provide due-to-calve dates if selling cows
• plan feed and labour management right through the dry-period, to next calving and mating, and
• refine your dry cow treatment (DCT) decisions with the vet

Early-aged pregnancy testing helps ensure individual cows are dried off at the right time, based on age, body condition score and accurate due to-calve dates. This enables dried off cows to be better allocated to dry cow mobs for wintering. This results in accurate feed allocation, especially on crop, and easier management and observation of springing cows through the calving transition.

Pregnancy testing methods

The main methods used for determining the pregnancy status of cows are rectal examination using a hand or ultrasound probe. Other methods exist such as milk or blood pregnancy testing.

Pregnancy status can be recorded aged in days or weeks for manual or ultrasound testing, while all methods can be used to record non aged results.

Early-aged rectal pregnancy testing by a skilled operator is the most accurate method to identify cows that are 5 weeks pregnant or more. If tested between 5 and 14 weeks of pregnancy it gives a good estimate of when cows conceived.

Early-aged pregnancy testing helps ensure individual cows are dried off at the right time, based on age, body condition score and accurate due-to-calve dates, and dried-off cows can be better allocated to dry cow mobs for wintering. In turn, this allows accurate feed allocation, especially on crop, and easier management and observation of springing cows through the calving transition.

Alternatively, pregnancy status may be estimated using continuous heat detection.

Some cows confirmed pregnant by pregnancy testing may fail to calve. This is most likely to be due to pregnancy loss (abortion) occurring after the pregnancy testing has been done. When the loss rate is higher than normal, a specific reason for abortion (e.g. neospora or BVD) should be investigated to prevent a recurrence.

For further information check out Chapter 18 of the InCalf book.

Milk pregnancy testing

When a cow is pregnant, she produces pregnancy-associated glycoproteins (PAGs). These can be detected in the milk from 28 days after conception. This means farmers can ask for pregnancy testing to be included alongside their routine herd test.

Milk pregnancy testing can provide a non-invasive, cost-effective option for farmers who aren’t early-aged scanning. But PAGs cannot give any indication of the stage of gestation therefore cannot age pregnancies and recording programmes will default to the last recorded mating.

If we know which cows are pregnant and when they conceived, we can have a good idea of when they will calve. The only way to find that out is by early-aged pregnancy testing.

Other ways to use milk pregnancy testing:

• Early in the mating period to identify pregnant cows. If identified, those cows could be managed separately, reducing the mob that still needs heat detection. But there needs to be caution with this method in case a cow loses her pregnancy while in the separate mob.
• To check for phantom cows during mating.
• To recheck any doubtful cows and identify any abortions to remove those cows before wintering.
• If there is a specific case requiring early testing for management decisions, for example culling in a drought, milk pregnancy testing could be a quick way to help make those decisions.

If using this tool in conjunction with early-aged pregnancy testing, it’s important not to record the results in your herd management programme: it could override the scanning results. But if this is the only method of testing used on-farm (or traditionally, the farmer only records empty cows), the results can be automatically updated in their recording programme.

If an animal has recently aborted, it will take two weeks for their PAGs to drop. This can lead to the milk pregnancy test returning a false positive.