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All AB herds - how do they stack up?
06 Sep 2017

The last two seasons have seen an increase in the number of LIC herds saying goodbye to natural mating bulls and doing AB for the whole mating period.  In the 2016 season, nearly 600 of our customers’ herds used all AB, almost double the number from 2014.

However, we have been hearing from the field concerns about whether going all AB will lead to a high empty rate.  So what do the stats tell us? 

We’ve looked at the last three years reproduction results of herds doing all AB (“all AB”) and compared them with the results of herds using AB and natural mating bulls (AB + bulls).  To get this comparison, we’ve analysed the results of spring calving seasonal herds that have a detailed InCalf Fertility Focus report in MINDA*.  This way we are only comparing herds with quality reproduction records.   Based on these selection criteria, we were able to analyse the results of about half of the country’s herds that are all AB.

2016 results overview (averages)

  AB + Bulls All AB All AB Difference
Herd Size 521 656 +135 cows
6-Week in-Calf Rate 65.5% 66.2% +0.7%
Not-In-Calf Rate 16.7% 16.9% +0.2%
Mating Length (days) 76 78 +2 days
Herd 3 Week Submission Rate 77.3% 82.3% +5%
Heifer 3 Week Submission Rate 78.4% 83.3% +5%
Conception Rate 51.7% 50.3% -1.4%
Herd 6 Week Calving Pattern 84.8% 87.0% +2.2%
Heifer 3 Week Calving Pattern 78.3% 80.6% +2.4%
Heifer 6 Week Calving Pattern 93.5% 94.6% +1.1%

In general, the all AB herds had slightly better results than the AB + bulls herds - see the table at the end of this article.

6-Week In-Calf Rate

For the last three seasons, the average 6-week in-calf rate of the all AB herds has been around 1% higher than the average of the AB + bulls herds.

Calving Pattern and Submission Rate

The slightly higher average 6-week in-calf rate of the all AB herds will have been helped by their tighter calving patterns and higher average submission rates.


Not-In-Calf Rate

The AB + bull herds had a slight edge here, but the difference was small - less than 1% (both groups had similar mating lengths). 

However, both groups have room to improve their not-in-calf rate.  Given the average length of mating was about 11 weeks, the expected not-in-calf rate is around 11%.  Lifting 6-week in-calf rates will help to meet this target.

Conception Rate

On average, the all AB herds had around a 1% lower conception rate each year than the AB + bulls herds, which is not entirely unexpected. 

The all AB herds are using AB for approximately 30 days longer, meaning that they will likely be inseminating less fertile cows in the later stages of the mating period, which will contribute to their overall conception rate.  In contrast, the AB + bull herds don’t have these cows/inseminations contributing to their overall conception rate.

Consistent use of All AB

29 herds in this analysis have been doing all AB for the last three consecutive years. Their results indicate that herds using all AB across consecutive years have around a 3% higher average 6-week in-calf rate than herds that use AB + bulls each year.

Location of All AB herds

There are all AB herds in every region of NZ.  Our 2016 data shows that the all AB herds made up 4% of all NZ dairy herds (seasonal spring calving herds that had a detailed Fertility Focus report, 3857 herds).

In 2016, more than half of the all AB herds were in the South Island (63%), compared to a more even split between the islands in 2014 and 2015.  Not surprisingly, it was three South Island regions that had the highest percentage of all AB herds in 2016:

  • Canterbury & South Canterbury - 17% of the herds in their regions were all AB herds
  • Southland - 15% of the herds in this region were all AB herds

All AB herd size

On average, the all AB herds are larger than the AB + bulls herds, but they range in size from just 81 cows all the way up to 2,608 cows.  The gap in herd size between all AB and AB + bull herds has been increasing over the last 3 years.  This is being driven by more South Island herds, whose average herd size is larger, moving to using all AB over the last 3 years.


To answer to the concern about whether going all AB results in a drop in reproductive performance, the stats indicate that All AB herds, on average, have slightly better reproductive performance than herds that are AB + bulls. 

Before switching to all AB though, you need to make sure you are set up for a successful all AB mating period.

  • Do you have good heat detection skills (>90% HD box, and <13% short returns)?
  • Will you have sufficient staff/resources to handle this extended period of AB? 

For more information on all AB mating, click here.

If you have any questions or want any more information, get in touch with the Repro Team at

*Herds included in the analysis for this article were spring calving seasonal herds that had a Detailed InCalf Fertility Focus Report (3857 herds).  The reproduction measures analysed were generated from data and information entered by herd owners and collected by LIC and DairyNZ.  Accuracy of the results reported here is subject to the accuracy of the data entered.

This table is a summary of the reproductive performance results for All AB and AB + Bull herds over the last three years:

  2014 2015 2016
  AB + Bulls All AB AB + Bulls All AB AB + Bulls All AB
Number of Herds Analysed 3201 145 3424 220 3469 388
Herd Size 543 +34 cows 530 +66 cows 521 +135 cows
6 Week In-Calf Rate 67% +1% 66% +1% 66% +1%
Not-In-Calf Rate 16% +0.5% 17% +0.9% 17% +0.2%
Mating Length (days) 78 -1 day 76 -0.2 days 76 +2 days
Herd 3 Week Submission Rate 81% +4% 80% +4% 77% +5%
Heifer 3 Week Submission Rate 82% +4% 81% +4% 78% +5%
Conception Rate 53% -1% 52% -1% 52% -1%
Herd 6 Week Calving Pattern 84% +3% 84% +3% 85% +2%
Heifer 3 Week Calving Pattern 75% +4% 77% +2% 78% +2%
Heifer 6 Week Calving Pattern 92% +1% 93% +1% 93% +1%


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