Measuring Reproduction Performance

Getting an accurate picture of herd reproductive performance offers a starting point for improvements.

It is important that these measures are accurate and can be calculated consistently year after year. This isn’t easy without a good record system. Taking little steps can often make the biggest gains, so accuracy is important. Accurate records begin with the birth of every calf.

If you measure the reproductive performance of your herd with the best measures and at the best times, you will be able to:

• confidently compare your herd’s reproductive performance to previous years and to the results achieved by top farmers;
• respond more quickly when the measures indicate that reproductive performance is not as good as desired;
• assess whether the changes you have made to improve herd reproductive performance have worked; and
• use reliable, accurate measures to help motivate your farm team and guide them towards better performance.

There are a number of measures available to assess reproductive performance. Some give you an overall picture; others an insight to a particular component of reproductive performance.

The best overall measures describe the rate at which cows get pregnant once mating begins and the number of cows that remain empty at the end of mating.

The following two measures are used to determine where your herd is at:

6-week in-calf rate

The 6-week in-calf rate tells you the percentage of cows in your herd that became pregnant in the first 6 weeks of the mating period. These cows will calve early in the calving period next year. Where artificial breeding (AB) is used for the first 3-6 weeks of the mating period, many or all these cows will be pregnant to an AB sire.

Six weeks makes sense because it represents two oestrus cycles, and the halfway point through a 12-week mating period. At about week six the difference in how quickly cows are conceiving is most evident between herds.

The 6-week in-calf rate also captures both the drivers of in-calf rate – the 3-week submission rate and the conception rate.

Farmers from throughout New Zealand and Australia have told InCalf why they value high herd reproductive performance. You can expect the following benefits from improved reproduction.

• Fewer not-in-calf cows allows increased culling of genuine low-producing cows, increases in herd size or a reduction in the number of heifer replacements required.
• Increased profit since earlier calved cows generate more milk income than later calved cows in most herds.
• More compact calving pattern with fewer late-calved cows, fewer not-in-calf cows and fewer cows requiring hormonal intervention.
• More cows getting in calf early in the AB period, providing more replacement heifers, or the potential for a shorter AB period.
• More AB heifers born early in the calving season which streamlines calf rearing and heifer management.
• Fewer days feeding dry cows and observing cows for calving problems.

Not-in-calf rate

The not-in-calf rate tells you the percentage of the herd that failed to become pregnant during both the AB and bull mating periods.

Historically we used the ‘empty rate’ but an empty rate tends to only include the percentage of cows scanned and recorded as empty after pregnancy testing. It is not as helpful as it can differ from farm to farm depending on who was present at pregnancy testing time.

Once you know where your herd is at, it is often useful to understand a bit more about what is contributing to the result. 

To get cows in calf quickly, they need to be inseminated early in the mating period and this is measured by the 3-week submission rate.

You also need to ensure that a reasonable proportion of inseminations result in pregnancy, as measured by the conception rate. To measure this, you have to be able to tell whether a cow conceived to insemination. There are two ways of doing this – directly through early-aged pregnancy testing or indirectly using non-return to heat.

Finally, a number of detailed measures are available to assess specific management areas. For example, 3-week submission rate of first calvers and pre-mating heats for the whole herd.

Why we shouldn’t use an "empty rate"

While the term empty rate is often used on farms to measure reproductive performance, it’s actually not easy to compare farm to farm and season to season. The ‘6-week in-calf rate’ gives us a solid indicator that allows you to compare performance with other farms, and season to season.

The percentage of cows who do not get in-calf during mating depends on a range of factors, but the final figure is heavily influenced by the ‘6-week in-calf rate’ and the length of mating.  Without knowing the length of the mating period and the cows that weren’t pregnancy tested we don’t have the full picture.

Unfair comparison

When Joe proudly tells his neighbour Mary that his “empty rate” is 11 percent and she tells him hers is 16 percent, we may not be comparing apples with apples.  Joe may have culled 20 cows before pregnancy testing and Mary may have mated her cows for two weeks less than him.

The not-in-calf rate is, essentially, everything minus the final in-calf rate - making it comparable for farms with similar mating lengths. This makes it ok to use for bench marking between years as well. An empty rate is not as helpful as it can differ from farm to farm depending on who was present at pregnancy testing time.

Each season we usually see an average of around 5 percent of eligible cows with no recorded outcome. They calved in the correct window and were present at the start of mating, but for whatever reason are not recorded as pregnant or not. These cows contribute to the overall reproductive performance and are included in the not-in-calf rate figure but not a recorded empty rate.

By using the ‘6-week in-calf rate,’ it’s easier for everyone to monitor reproductive performance and it can help you to be better able to drill down and identify how to improve this.  By ditching the use of ‘empty rate’ and using a truly comparable measure we can fairly benchmark our performance from year to year and against other farms.