Friday, March 29, 2024

Testing times for pregnancy

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The time to determine whether all the hard work that has gone into mating has paid off is rapidly approaching. Pregnancy testing provides the opportunity to check not only which cows are pregnant or not pregnant, but also to calculate the six-week in-calf rate, to determine the likely calving pattern for next season, and to find late calving cows that could be sold to tighten calving patterns.
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Pregnancy testing either by scanning or palpation is most accurate between about 5 and 12 weeks after a given mating.

If the main aim of pregnancy testing is to get an accurate estimate of the six-week in-calf rate, doing the first test about 12-13 weeks after the planned start of mating is ideal. Testing at this time allows the date of conception for every cow to be estimated. If the actual conception date of individual cows within the first six weeks of mating is less important, but you want to establish whether cows did or didn’t conceive in the first six weeks, the first testing can be pushed back to 16-18 weeks after the planned start of mating.

For herds mating for 12 weeks or less, it might be feasible to do all the testing on one day and get a reasonably precise estimate of the six-week in-calf rate, but individual conception dates for cows conceiving the first six weeks won’t be precisely determined.

Pregnancy testing is reasonably precise, but various factors will influence how accurate it actually is.

Inaccurate cow identification because of a double-up on tag numbers, for instance, or dirty tags which result in misreading of cow numbers, can result in the wrong results being applied to the wrong cow. To make everyone’s job easy, it is important to check there are no double-ups of the tag numbers and the tag numbers are readable.

Using recording sheets which list every cow number in the herd, preferably with the number of days pregnant the cow might be, based on the last three recorded mating dates, also increases accuracy.

Reports are available from Mindapro (this can be printed out by selecting View/Reports/Management Reports/ Pregnancy Test Worksheet and filling in the appropriate details) or other software packages such as Infovet.

A good way to use these sheets is to get the vet to give you the number of days pregnant and if the vet’s call is within seven days of a known artificial insemination or bull mating date, accept that the mating date is likely correct.

If the vet’s call is more than seven days from a recorded mating date, which commonly happens where there are unrecorded bull mating dates, the vet’s call should be accepted.

To improve the accuracy of recording get the recorder to call back the cow number and days pregnant for double-checking. Where double-ups of management tags are discovered, the lifetime ID should be double-checked and the discrepancy resolved.

As a triple-check, it is worth marking cows that are called empty and cross-check against the recording list, because culling the wrong cow is an expensive mistake.

Pregnancy testing demands a lot of concentration, so the set-up should be comfortable for the vet and the recorder. Minimise extraneous noises and excessive light. Testing during milking might save an additional yarding, but take care not to rush it, because there may be an increase in errors.

The value of the pregnancy test data will be maximised where it is entered into software such as Mindapro, Maestro or Infovet. This will allow the Fertility Focus Report to be generated and a more precise due-to-calve list produced. In the absence of pregnancy test data, the due-to-calve list is based on the last recorded mating for any specific cow to which the gestation length of the sire (or 282 days if it is a bull mating) is added.

Once the information is in, the herd’s performance can be benchmarked and if a 78% six-week in-calf rate is not achieved, the data can be further analysed to determine which age groups, breeds, disease groups and so on are causing the sub-optimal performance.

Pregnancy testing is an important management tool. Removing the right cows for the right reasons and at the right time based on precise data will be more economic than incorrectly culling even a small percentage of cows, which could happen without pregnancy test data.

Scott McDougall is a vet with Cognosco, Anexa Animal Health, Morrinsville.

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