On dairy farms at calving time, a group of cows appears every year. These cows were pregnancy-tested in calf but are now found to be empty. Why does this occur and what can we do to minimise the numbers?
There are four reasons why cows diagnosed as pregnant end up empty at the end of calving:
1. ‘Natural' pregnancy loss
2. ‘Abnormal' pregnancy loss due to disease
3. Incorrect recording
4. Incorrect diagnosis
There is always a percentage of ‘natural' pregnancy loss in any herd. Most of these are probably due to genetic abnormalities of the foetus or unknown reasons. It has been estimated that 10% of pregnancies are lost before five weeks - some of these will appear as long returns. A large trial conducted in the Waikato in 2005, in which cows were pregnancy-tested every 2-4 weeks throughout their pregnancy, showed that from five weeks' gestation until calving, 7.2% of pregnancies are lost. This means that for an average 400-cow herd mating for 12 weeks and pregnancy-testing 6 weeks after the bull comes out, 10-15 pregnancies will be lost between pregnancy-testing and calving (3.75%). In our experience, most farms do not lose this many. However, if you are experiencing greater than 2% pregnancy loss, seek help. There are many possible causes that can be investigated including BVD virus and Neosporosis.
In recent years, herds have become larger, and due to improvements in technology, pregnancy-testing has become faster. This has lead to a greater risk of human error in recording pregnancy-testing results. The following things are very important to reduce recording errors:
- Pregnancy-test at the right time
Accurate ageing of pregnancy can only be done between 6-12 weeks of gestation
- Timing depends on what you want to know
In-calf or not in-calf; estimate of due calving date; calving before or after a specified date
- Are you planning on inducing cows?
If so, cows must be pregnancy-tested at the right time to determine specific ages
- The recorder needs to be competent and focused, repeat cow numbers and result back to the vet, and not be distracted by cell phones and cowshed banter
- Have someone marking cows and reading tags - a check for the recorder
- Print off your MINDA mating record sheet and use this to record with
- Ensure tags are clean, easily read and there are no double-ups
- Keep permanent records
If you have a split calving herd, each herd should be pregnancy-tested six weeks after mating ends to ensure accurate records. It is difficult to accurately distinguish spring and autumn calvers once pregnancies are greater than 12 weeks. Pregnancy records are very important in split-calving herds so that cows are dried off at the right time to allow an adequate dry period and avoid bulk tank somatic cell count issues.
Totally Vets veterinarians are highly trained in pregnancy diagnosis so the incidence of a cow being called pregnant when she is empty, or vice versa, should be extremely rare. Ageing and early/late pregnancy diagnosis will be 90% accurate to within 2 weeks of gestational age.
Talk to us if you have concerns about the number of cows turning up empty in your herd at calving. There are a number of ways we can help, including planning pregnancy-testing timing to achieve the information you need. We can also provide a recorder.
