Cow Reproduction and Mating Overview


3 min read

Preparation for mating Timing of insemination Assessing AI technique Causes of low non-return rates Genetics Fertility breeding values Sire selection and fertility genetics Crossbreeding adds hybrid vigour Gestation length Selecting sires for dairy beef opportunities Selecting bulls to minimise calving difficulty

Dairy cow fertility is essential to a productive dairy farming business. It is important to consider areas to focus on, in order to maximise the herd's reproductive performance. Improving reproductive performance can make a sizeable impact on your bottom line, as well as simplify your farm management. 

Preparation for mating

In New Zealand, professional AB technicians do the majority of inseminations. They are responsible for semen storage, handling, insemination technique, and have control procedures in place to provide the best possible service.

Conception rates are substantially reduced when semen is not stored and handled correctly or when technique is flawed. Australian InCalf research has shown that at least 40% of DIY technicians could have at least a 5% increase in conception rates by improving insemination practices.

In preparation for mating ensure you have a well-planned system with your farm team and have the necessary supplies at hand. Assist your AB technician and complete the on-farm mating record book before they arrive and if multiple sires are being used, organise/mark cows to help the technician get the right straw into the right cow.

Timing of insemination

Cows should be inseminated at the first opportunity, after they have been seen in standing heat. Cows seen in heat at the evening milking should be inseminated the following morning. Cows seen in heat at the morning milking should be inseminated that morning. There is no advantage in inseminating more than once per day.

When to inseminate cows

  • Cows are in standing heat for 18 hours on average (range 6 - 24 hours).
  • Ovulation occurs 14 hours on average, after the end of standing heat.
  • Good quality semen has an effective life of about 28 hours in the reproductive tract of the cow.
  • On average, the ovum remains fertile for about 6 hours.

Assessing AI technique

Conception rates are reduced substantially when semen is not stored and handled correctly, or when insemination technique is flawed.

The non-return rate can provide an early warning of a low conception rate and is a worthwhile first check. If, from your Fertility Focus report, the 2 to 24 day non-return rate for your herd is less than 64%, or conception rate is less than 53%, you need to investigate potential causes.

Causes of low non-return rates

Causes to investigate and recommended action.

Farm related

  • Poor body condition at calving or excessive loss of body condition following calving – review body condition score targets and herd nutrition.
  • Inaccurate heat detection – review your heat detection programme.
  • Excessive numbers of late calvers – review calving pattern.
  • Excessive numbers of treated non-cyclers.

There are other possible causes of low non-return rate and low conception rate. You may need to seek help from an InCalf adviser.

Technician related

  • Poor inseminating practice – report your concern to the field supervisor of your AB service.

It is difficult to assess an AB technician from a single farm, however, their field supervisor can access results over several herds. These results can also be compared with those obtained by different technicians working in the same herd.

Assessing technician non-return rate

Breeding company

The 18-24 day non-return rate is used by breeding companies to monitor AB technician performance. The eligible inseminations exclude short returns (24 days). Be aware that the (2 to 24 day) non-return rate reported on your Fertility Focus report is likely to be 10% less than the 18 to 24 day non-return rate of eligible returns used to monitor AB technicians.

DIY technician

If you are a DIY technician a disadvantage is that if the non-return rate or conception rate is low, it is difficult to determine whether your technique needs improving or whether other factors are reducing the conception rate.

Australian InCalf research has shown that DIY technicians could achieve an increase in conception rates by improving insemination practices. Consider the following actions to help improve your technique:

  • Practice your technique on cows in heat before mating starts (this can be done without using semen by placing a sheath over the pistolette).
  • Have your technique checked by the local AB service supervisor on the farm.
  • Attend a refresher course if you have not done one for two years or if you are not confident with your technique.

For information on semen storage, handling, and insemination technique, refer to the InCalf book.


Genetics plays a role in an animal’s reproductive performance, for the animal itself and the sire she's mated to.

New Zealand’s seasonal dairy farming system entails a condensed calving pattern with cows required to conceive within approximately 12 weeks of the planned start of calving. This has resulted in strong selection for fertility through culling of non-pregnant cows and relatively strong emphasis on fertility in Breeding Worth (BW), the national breeding objective that drives sire selection.

Fertility breeding values

Fertility breeding values (BVs) are comparative measures expressed as a percentage of daughters that are confirmed pregnant in the first six weeks of mating. The fertility BVs can be used to compare sires of all ages, breeds and crosses in New Zealand.

Fertility BVs for bulls and cows are relative to a genetic base, being the average of cows born in the base year. So cows with fertility BVs of 0% have the same genetic merit for fertility as the base cows born in 2005.

In comparing cows with fertility BVs of +5% (high genetic merit for fertility) with cows with fertility BVs of -5% (low genetic merit for fertility), you can expect 10 more high-merit cows per hundred to re-calve in the first 6 weeks of the herd’s calving period.

Bulls transmit half their fertility BV to their daughters. The other half comes from the dam.

See Breeding values for more information.

Sire selection and fertility genetics

Some artificial breeding (AB) sires produce daughters that are genetically more fertile than others. This means that the genetic make-up of your herd for fertility may be a little better or worse than the average herd.

You can check your herd's fertility genetics by requesting your herd’s average fertility breeding value (BV) from your herd improvement organisation.

Breeding Worth (BW) takes reproductive performance into account, ensuring there will be ongoing genetic progress long term in cow fertility.

Farmers who are struggling with reproductive performance could find it valuable to specifically target bulls that rank well for fertility.  This will effectively increase the rate of gain in fertility genetics within their herd, and this should have a large impact on their herd’s overall reproductive performance.

Crossbreeding adds hybrid vigour

If you are breeding crossbred cows they will have additional hybrid vigour for fertility. New Zealand Animal Evaluation data measures the hybrid enhancement of fertility beyond the effects of breeding values.

The hybrid vigour advantage for a first cross animal is that the 6-week in-calf rate is around 3.4% higher than you would expect from mating parents of the same single breed.

The hybrid vigour advantage for subsequent crosses is that the 6-week in-calf rate is around 2% higher than you would expect from mating parents of the same single breed.

Crossbred AB sires will retain a 1.7% hybrid vigour advantage.

Gestation length

In New Zealand, the average gestation length of dairy cattle is 282 days, but there is genetic variation around this.

Dairy sires gestation lengths can be found in the Animal Evaluation section.

Interest in short gestation breeding options has increased and some farmers include short gestation length sires in their mating programme, at the tail end of AB or as an AB restart near the end of mating.

You should be aware of the gestation length BV of the sires you are using (both beef and dairy), as it will affect he calving date of your cows.

See Calving pattern.

Selecting sires for dairy beef opportunities

A wider range of beef breeds are available from most breeding companies including Wagyu and Stabiliser as well as more traditional breeds such as Angus and Hereford.

Selecting sires that have desirable traits such as growth rate to 400 days, gestation length and calving ease are critical when mating a percentage of the herd for dairy beef.

Beef + Lamb New Zealand have a programme of work testing the performance of bulls with EBV’s that indicate they are likely to be excellent bulls for dairy beef systems Read more here.

Selecting bulls to minimise calving difficulty

Subsequent reproductive performance is worse after an assisted calving.

Some sires, especially Holstein-Friesian, cause higher rates of assisted calving when mated to yearling heifers.  This is a direct genetic effect of the bull.

This sire effect is reflected in a sire’s calving difficulty BV.

A sire's calving difficulty BV predicts the percentage of assisted calvings expected when he is mated to yearling heifers. It can also be used to identify bulls that are expected to increase the rate of calving assistance for cows carrying the bull’s calves.

When artificially inseminating yearling heifers, use sires proven under New Zealand conditions with a low calving difficulty BV.

Last updated: Aug 2023

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