Knowing the pregnancy status and conception timing of cows is vital for making informed management decisions, such as individual cow drying off dates.
Pregnancy testing methods
An effective pregnancy testing strategy is essential in measuring and monitoring your herd’s reproductive performance for:
- 6-week in-calf rate and not-in-calf rate in seasonal and split calving herds.
- 100-day in-calf rate and 200-day not-in-calf rate in year-round calving herds.
There are two main methods for pregnancy testing:
- Manual (rectal) examination of the cow’s reproductive tract which is carried out by an experienced operator using manual palpation and/or an ultrasound probe. Pregnancy testing with foetal aging helps predict the next calving date with some accuracy. You can use this information to identify dry-off dates more accurately for individual cows and provide a 60-day dry period. Foetal aging is currently only possible using manual (rectal) pregnancy testing by an experienced operator and most accurate when cows are between five and 15 weeks pregnant.
- Laboratory testing of a sample of milk or blood is obtained from the cow to determine the level of specific proteins or hormones associated with pregnancy.
Advantages of laboratory testing for pregnancy:
- Mostly very accurate.
- Non-invasive – there is low risk of abortion.
- Convenient – especially with ‘farmer collection’.
- Cost-effective - when small numbers of animals require testing.
- Samples can be stored before sending for testing.
Disadvantages of laboratory testing for pregnancy:
- Some only moderately accurate at identifying empty cows.
- Unable to age pregnancies with accuracy.
- Results not immediately available as samples sent to a laboratory for testing.
- May give false positive results in cows which have recently calved and/or recently lost a pregnancy.
- Require extra handling which can lead to increased errors in identification.
Improving testing accuracy
Generally, around 70 per cent of cows will calve within a week of their due date based on early rectal pregnancy test results. Typically, 10 per cent of cows calve 10 days before and another 10 per cent calve 10 days after their due date. This natural variation in pregnancies means that pregnancy testing cannot provide exact expected calving dates in all cows.
The accurate identification of animals and careful recording of results is essential for successful pregnancy testing. Always bring a list of cows to be tested that includes the number of weeks that they would be pregnant if conceived for each of her recent matings. All animals should have clear identification tags or freeze brands. There should be no duplicate identifications and have a good recording practice in place. A result recorded against the wrong cow is a wasted measurement and lost information.
You may also need to consider follow-up pregnancy testing. This is recommended because for very early pregnancy testing, up to 10 per cent of confirmed early pregnancies are subsequently lost. Consider re-examining cows diagnosed testing under 6-weeks of pregnancy, at a later date, to confirm that they have held the pregnancy.