LIC | Four quick questions to consider before you stop AB

Four quick questions to consider before you stop AB

AB mating is a busy time on farm, but it speeds by quickly and before you know it it’s coming to an end. The natural mating period follows on most farms, with service bulls ready and waiting. 

As the season unfolds, your farm’s plan may need adjusting. Mating is no different. 

Before you decide to stop AB mating, consider these four quick questions.

  1. Am I likely to get enough replacement heifer calves next year?
  2. Am I going to qualify for my LIC InvestaMate discount?
  3. Do I have enough service bulls on hand to meet demand and minimise my herd’s final empty rate?
  4. Do I have synchrony returns to consider in my plan?

You can use the guidelines below to estimate your numbers using your herd information for the mating season to date.

If things aren’t quite panning out as you’d envisaged, you can make adjustments to your plan such as extending AB mating to:

  • generate more replacements, 
  • reduce bull-power requirements, 
  • cover returns to synchronies or 
  • compact next year’s calving.

ReplacementsEstimating heifer replacement numbers

As a rule of thumb, we estimate that it takes close to five (5) inseminations (insems) to breed each replacement heifer and have her complete a first lactation in the herd, however numbers do vary between seasons and herds. 

Total replacement semen insems used divided by 5 = estimated expected heifers in the herd.

Note: The 5 insems figure allows for losses between the point of conception and the end of the first lactation as well as for some discretionary culling for reasons other than reproductive failure of cows that may be pregnant to AB.

Estimating bull power requirements

Use the steps below to estimate how many bulls could be required on your farm, inserting your own figures for herd size, inseminations and conception rate. 

(Conception rate is available for previous years on the Fertility Focus™ report on MINDA® for most herds with sufficient early aged pregnancy testing information).

  1. Calculate your expected number of pregnant cows:
    Total insems x conception rate (52% is national average) = estimated pregnancies.
  2. Subtract the pregnant cows from the total herd size to get non-pregnant cows.
  3. Divide the number of non-pregnant cows by 15 to get the estimated number of bulls required on farm to meet natural mating period requirements at the ratios explained in the assumptions below.

For example, a 1000 cow herd that has had 1200 matings:

1200 x 50% = 600 estimated cows pregnant
1000 – 600 = 400 estimated cows non-pregnant 
400 / 15 =27 estimated bulls required on farm (without spares).


Industry recommended bull power allows:

  • one healthy fertile two-year-old bull per 30 non-pregnant cows, and 
  • two teams of bulls, rotated every 24 to 48 hours. 

So that’s one bull per 15 non-pregnant cows on farm. And remember, you’ll need more bull power in the paddock on the days of returns to synchronies.

Information on bull numbers and AB options for synchrony returns plus an alternative method for estimating bull power requirements is available from DairyNZ® in The InCalf book for New Zealand Dairy Farmers, page 129.

Contact your local LIC Farm Solutions Manager for more information or to discuss AB options that will help you reach your goals.

Disclaimer: Any advice, tasks or suggestions given on this website (“advice”) are of a general nature only and may not be suitable for your individual herd requirements.  We recommend that you discuss your individual herd requirements with your veterinary and farm advisory professionals. Any results from the advice given on this website may vary and LIC gives no warranty that the intended outcome will be achieved.

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