Extending AB Period


3 min read

Pros Cons Advice Considerations

Changing mating management on your dairy farm can offer benefits but comes with potential risks. This page outlines the pros and cons of options such as combining artificial breeding (AB) with natural mating, extending the AB period, or using AB exclusively. Advantages can include reduced disease risk, more dairy replacements, potential extra income, and better performance monitoring. However, risks include potentially poorer reproductive performance and logistical challenges. Every farm's situation is different, so carefully assess yours to determine the best approach. If changes are made, ensure communication with all involved and develop a solid mitigation plan for any potential issues.

Heightened biosecurity in New Zealand, among other reasons, has led some farmers to consider changing their mating management on farm.

Whether you are thinking of combining artificial breeding (AB) and natural mating bulls, extending the AB period to reduce the number of bulls needed, re-starting AB in the last few weeks of mating, or implementing AB through the whole mating period, the risks and benefits of each option need to be considered.

Every farm’s situation is different and will determine the best option for that farm, so it’s worth assessing your current situation to determine if you should consider a change on your farm.


  • Reduces risk of introducing disease as less or no bulls are required
  • Increased number of dairy replacements
  • Opportunity to create extra income from surplus dairy replacements and higher value calves (e.g. beef)
  • Potentially increased genetic gain (more selection pressure on replacements is possible)
  • Better monitoring of entire mating performance (all matings are recorded)


  • Risk of poorer reproductive performance, especially in herds where performance is not optimal. Talk to your advisor. Discuss the checklist below to help you identify what your current situation is and consider whether making changes in the upcoming season or whether a staged approach should be taken.
  • Extended heat detection period
  • Silent/quiet heats have a higher potential to be missed - good results are reliant on excellent heat detection maintained throughout the entire AB period
  • Fewer animals cycling as more become pregnant making heat detection more challenging
  • Potential for incorrectly inseminating pregnant cows if reliant on human heat detection (cost, loss of early pregnancies)
  • Increased logistical considerations – staffing, heat detection aids, semen and tech


  • Extending the AB period or going all AB will not be suitable for everyone.
  • If you decide to extend your AB programme, communicate this to all of those involved in making your plan happen - your vet, your semen supplier, your AB tech, your rural professionals and your team on farm.
  • If you increase the use of synchrony of heifers and cows, plan ahead to cater for the increase on the numbers of cows calving within a very short timeframe, from a feed demand point of view, in the following calving season.
  • If you plan to change the approach with your heifers and use AB, discuss how to maximise their performance with your vet. Liveweight, general health and BVD control, as well as the practicalities and logistics of synchrony programs, grazier facilities and technician services, should be considered.
  • Further information on areas affecting a herd’s reproductive performance and management options can be found in the InCalf book.


Even if you don't meet all the criteria below, you can still extend your AB period or adopt all AB. However you will need to have a solid plan in place for how you are going to mitigate those criteria you don’t meet so that you set your herd up for a successful mating period.

Repro performance is at national average or higher

  • A 6-week in-calf rate above 67 percent
  • A 3-week submission rate of 80 percent or higher 
  • A conception rate of 50 percent or higher
  • Less than 20 percent short returns
  • Fewer than 15 percent cows treated for anoestrous

Your herd is healthy and primed to have a successful mating

  • BVD free (BVD can have strong reproductive performance consequences)
  • No increase in cow health problems through calving (e.g. milk fever and mastitis)
  • First calvers have reached their target liveweight for calving
  • No increase in late calvers

You have the skills and staff to carry out prolonged heat detection

Extended AB or all AB makes accurate heat detection even more critical as these can increase heat detection to 10-12 weeks. For more information see Heat Detection.

The cost benefit fits your plan

Talk to your farm adviser, your vet and a farmer that has already extended AB or gone all AB for advice.



  • Allows a shortened AB period
  • Reduces heat detection requirements – staff, heat detection aids etc.
  • Allows mating to occur where AB is impractical (i.e. R2’s at run-off)
  • Can be kept and used for multiple seasons
  • Retain some value as they can be sold or sent to the works for a return


  • Biosecurity risk – can be well managed through testing and/or vaccination with some diseases (i.e. Tuberculosis, Johnes disease, BVD, Leptospirosis) but Mycoplasma bovis presents a more difficult situation
  • Cost
  • Associated bull issues – aggression, lameness, H&S etc
  • Availability of leasing bulls
Last updated: Sep 2023
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