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Pregnancy testing is key in managing your dairy herd. It tells you which cows are pregnant and their conception time, which helps you to plan effectively. This includes determining when to cull empty cows, deciding the right time to dry off cows, or organising feed and labour management. Several methods exist for pregnancy testing, like rectal examination using hand or ultrasound, and milk or blood testing. Early-aged rectal testing is highly accurate for identifying pregnancies at 5 weeks or more. Milk pregnancy testing can also be effective but doesn't provide information about gestation stage. Remember, cows confirmed pregnant may still fail to calve due to potential pregnancy loss. If this happens more than usual, investigate specific causes to avoid recurrence.
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:
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.
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.
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:
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.