Farm Ireland

Tuesday 20 February 2018

Mating time key to empty rates

Mary Kinston

On many farms the bulls have now been removed and the empty cows are becoming quite evident. As a result the timely question of what is your herd's "empty rate" has come up at recent discussion groups. For some, overall mating appears to have gone well with empty rates of 4-8pc. For others, even with favourable weather, empty rates of greater than 15pc have been reported.

If you fall into this latter category you may be questioning where it has gone so wrong? What is Mr 4pc doing so right? Before you go picking his brains for a cure to your infertility issues, just remember to quantify that empty rate with one important question -- how many weeks did you mate for? This is more important than you think as illustrated for five herds (A-E) of 100 cows in the table right.

So is the empty rate of 6pc so good? The in-calf rates above follow a bell shape curve. But is an empty rate of 10pc after 10 weeks of mating (nine cows in calf per week) any better than a herd that achieved an empty rate of only 6pc after weeks (only five cows in-calf per week). Clearly empty rate is not a good measure of a herd's fertility by itself, and should be tempered with mating weeks.

Ideally, as farmers we would all quote empty rates to no later than week 12, as any animal calving after week 12 is essentially calving after the start of mating. As we all know this late calving animal is one of the hardest to get back in-calf, and if she does, she's still likely to be calving late, and also has a reduced milk production due to shorter lactation length.

So if your empty rate is causing you concern the next step is actually to take some time to analyse your herd's recent mating and calving data. This requires a good set of records. Herd Plus can help you with this. A herd's reproductive performance is farm specific and there is generally no one silver bullet that will fix all problems.

This may seem an odd time to be looking at calving and mating performance because it's all done and dusted.


But it makes sense because it gives you a chance to do some investigatory work if required, and come up with a reproduction management plan for next year.

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The pregnancy rate (PR) at six, nine and 12 weeks of a herd is a far better measure of reproductive performance. So scanning can be a good start to confirm and age pregnancies.

Next, determine your submission rate (SR) and conception rate (CR) at week three of mating as percentages. Pregnancy rate is a result of both submission and conception rates (i.e PR = SR x CR).

For example for a 100 cow herd, if 64 cows were submitted for mating in the first 21 days, you have a submission rate of 64pc. If 35 of these 64 cows held a pregnancy then you have a conception rate of 55pc (35/64 x 100). The pregnancy rate for the first three weeks in this example is 35pc. This can be repeated for week 4-6, 7-9, 10-12.

Having done this you can identify where you need to improve. You should aim for a submission rate of >90pc and a conception rate of >50pc. If you achieved these figures you would actually have a six-week pregnancy rate of around 70pc.

Therefore in the example above it is clear that the conception rate is reasonably good, but submission rate is poor.

The farmer in this example should concentrate his efforts on factors that affect submission rate such as heat detection, percentage of cows calved less than 30 days before the mating start date, bull management etc.

Consider asking your vet for some assistance on this matter.

Doing this will help you to focus on factors that you can control, and provide you with a few simple changes which could make a big difference.

Mary Kinston is an independent dairy consultant based in Co Kerry. Email:

Irish Independent