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Pregnancy Testing

The Benefits of Pregnancy Testing

1. Planning drying off dates

   Cows that have too long or too short a dry period cost money. If you know the expected calving dates of the cows accurately, you can dry cows off according to these dates, maximising the milk yield from later calving cows whilst ensuring all cows have an adequate dry period.

    

2. Planning induction programs

   Late calving cows can be identified well in advance, and an induction program planned before the start of drying-off. This allows the most effective induction program to be used on selected cows that have been well prepared.

    

3. Detect empty cows

   An empty cow will start to be a cost on the system once she is dried off. The cost of not knowing that she is empty is the extra feed she consumes during her dry period until she is finally discovered to be empty, and the cost of lost milk which would have been produced if she had been milked through.

    

4. Feed budgeting

   A knowledge of the expected calving pattern will assist in the planning of feed budgets; eg- the purchase of extra feed such as hay or silage.

    

5. Purchase or Sale

   Preg testing cattle for sale provides both the vendor and the purchaser a level of security. Preg testing results enable the purchaser to select which cattle are suitable for purchase, and the vendor is provided with the guarantee that the cattle up for sale are pregnant.
   If you are planning to sell cattle ensure that the stock are preg tested and you get a certificate of the results.

    

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Methods of Preg Testing

• Farmer Observations

   

  1. Return to oestrus
     The close observation of cows is a reasonably reliable indicator of pregnancy status in small herds ( <100 cows) with an operator who knows the cows very well. However up to 10 % of pregnant cows can show some sign of heat during pregnancy and empty cows don't always show heat.

      

  2. Ballottement of the abdomen
     In the late stages of pregnancy ( >6 months), the foetus may be palpable through the right flank. This is unreliable in large frame cows or cows in heavy condition.

      

  3. Milk production
     Udder development in heifers is a reasonably reliable sign of pregnancy from 4-5 months of gestation.
     Empty cows often milk better than their pregnant herd mates. This isn't always reliable due to individual cow differences, but may indicate cows to check before drying off.

      

• Rectal Palpation

  Performed by a skilled operator, rectal palpation is very accurate. Pregnancy can be confirmed from 6 weeks (later in fat cows), and the pregnancy can be aged. The accuracy of ageing depends on the skill of the operator and the stage of pregnancy.
  There is great variation in the facilities and subsequent ease of use of manual preg testing between farms.

   

• Milk Testing

  If combined with herd production testing, the use of milk testing can be very convenient

   

  1. Oestrone Sulphate
     This test is quite good at detecting pregnant cows that are more than 5 months pregnant ( 98% ), however empty cows should be checked manually before being culled.

      

  2. Progesterone
     This test is quite good at accurately detecting empty cows ( ~ 90 %), but not very good detecting pregnant cows ( 30 - 35 % of diagnosed pregnant cows will be empty). This test is not used much in Australia or overseas.

      

• Ultrasound Testing

   

  1. Flank Ultrasound
     
  2. Rectal Ultrasound
     A video display shows what is beneath a probe placed in the rectum. Performed by a skilled operator, ultrasound is very accurate at detecting pregnant cows. Ageing of pregnancy in the early stages (3 - 14 weeks) is possible but takes considerably longer than a 'Yes' or 'No'. Empty cows should be checked manually before being culled. Well prepared facilities are required.

      

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Comparison of Pregnancy Diagnosis Methods

It is easy to see from the above table that manual rectal palpation gives the most accurate diagnosis of empty and pregnant cows, and is the most accurate method for estimating the age of early and late gestation pregnancies. It is also the least expensive option in most situations. If the facilities make rectal palpation impossible milk testing for oestrone sulphate may be easier, however empty cows should always be checked manually before being culled. Remember, if you are using any methods other than manual palpation, it can be very expensive to cull a pregnant cow by mistake. Always check empty cows by manual palpation before culling.

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Accuracy of Manual Rectal Palpation

Performed by a skilled operator, manual rectal palpation is close to 100 % accurate for diagnosing cows pregnant or empty. The accuracy for ageing the pregnancy is dependant on the stage of pregnancy.

The most accurate results are obtained with pregnancies between 6 and 12 weeks in calf, and even up to 16 weeks. Better than 90 % of the estimated stage of pregnancies will be within 2 weeks of the actual stages. Greater accuracy can be achieved if good breeding records are available at the time of preg testing, allowing the stage of pregnancy to be matched to the day of conception.

If cows are preg tested at 4 to 6 months of pregnancy, it is not always possible to differentiate between stages of pregnancy 3 weeks and sometimes even up to 6 weeks apart.

At more than 6 months of pregnancy, errors of 4 to 6 weeks will be made in up to 25% cases, making it difficult to confidently dry cows off at late stages, according to these results.

If you are wanting to dry cows off every 1 to 2 weeks, maximising the milk yield from each cow, you need to be confident of each individual cow's stage of pregnancy.

To minimise errors cows should be preg tested when they are less than 12 weeks pregnant.

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Pregnancy Testing Facilities

There are three basic setups for efficient pregnancy testing of dairy herds. There are many variations on these depending on the characteristics of your dairy. The basis principles of a good setup are outlined in our November 1999 newsletter.

 

• Rotary Dairies

  An examination platform allows for many procedures to be performed with ease and speed, often during milking. It can be used for applying heat detection aids, examining cows for signs of heat, AI, preg testing, vaccinations and many other procedures.

  The safest platforms for the cows and operators are a couple of inches above the rotary platform to allow milk lines to pass underneath and are positioned with a few inches overhanging the rotary platform to prevent cows feet dropping of the edge of the platform whilst being examined.

  The platform should be long enough to access 4 - 6 bails at once and deep enough to allow people to easily pass behind a preg tester or an inseminator as they are working. A longer platform will allow multiple operators to work at once, which minimises the time taken to perform tasks. We commonly have three vets preg testing at once, checking 200 cows an hour.

   

• Herringbone Dairies

  Cows can be preg tested in herringbone dairies by positioning planks for the operators to stand on. These planks can be supported by drums in the pit or boards across the pit. This is the most common method we use when preg testing, and this method also allows for multiple operators.

  This method can be dangerous in unsuitable dairies, where the cows are standing too close to the edge of the platform or the rail at the cows tail is too high. If a cow slips there is little time to remove your arm before it will contact the rail.

  Obviously this method cannot be used during milking, and the design of some dairies doesn't allow enough room for operators.

   

• Herringbone Race

  A herringbone race outside the dairy can be used to perform tasks during milking. The race should hold the same number ( or more ) of cows in one side of the herringbone.

  In most sheds, this will allow multiple operators to keep up with the flow of cows after being milked. It is sometimes useful to have a drafting yard to hold excess cows if cows are being milked fast, or the race holds less cows than get milked at any one time.

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A Pregnancy Testing Program for Your Herd

If you require the most accurate results for planing drying off and inductions, cows should be preg tested when they are less than 12 weeks pregnant.

The recommended program for most herds is:

1. 12 weeks after mating start date

   For most herds with a 6 week AI period this will be all cows joined to AI. If the AI period was less than 6 weeks preg test the whole herd. This will identify expected calving dates for all early calving cows.

    

2. 18 weeks after mating start date

   Preg test all cows which were not diagnosed pregnant at the earlier visit plus any cows which have been seen on heat. This will identify all cows which are early enough to calve naturally, ie. the first 8 weeks of calving.
   This visit is not as important in herds with a tight calving pattern, where the bulk of the cows have been preg tested in calf to AI.

    

3. 7 weeks after the bulls are removed from the herd or 26 weeks after mating start date.

   Preg test all cows not detectably pregnant at earlier visits and any seen on heat.

    

If calving is split or spread out, monthly or 6 weekly visits similar to the first two visits will give the greatest accuracy.

 

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