Farm Ireland
Independent.ie

Tuesday 19 September 2017

Mary Kinston: Submission rate above 80pc is the key to a good six-week in calf rate

Mary Kinston

Farmers who started calving around the beginning of February are close to, or over, six weeks of mating. Breeding is a stressful time on dairy farms, especially where AI is being used, due to the plethora of breeding dates and returns to service to be remembered.

The percentage of cows that received at least one insemination or mating in the first three weeks of the mating period is known as the three-week submission rate.

Discussion group farmers have are reporting a reasonable performance this year, with the majority achieving a greater than 80pc performance rate in the first three weeks.

Indeed, there have been a number that have achieved excellent performance rates of more than 90pc.

Note that the submission rate must be above 80pc if you hope to achieve a good six-week in-calf rate. Many have commented on the fact that cows have shown strong signs of heat this year compared to previous ones.

I believe that condition score at mating was better this year due to a good condition score at calving, which in turn had a positive effect on mating performance.

It's great to hear the debate on the finer points, such as the application length and width, frequency of top-up and changing colours for tail painting.

Weeks 4-6 of mating provide the opportunity to make some assessment of mating performance in terms of conception.

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Farmers often presume a cow is pregnant if she does not return to heat after service, and the non-return rate (NRR) is often used to estimate the conception rate.

As the normal cycle of a cow is 18-24 days, the non-return rate is best assessed after 24 days. For example, for a herd of 100 cows that has a submission rate of 85pc (85 cows mated in weeks 1-3) -- if 28 cows repeated over the next 24 days (weeks 4-6) it would suggest that 57 cows were in-calf, resulting in a non-return rate of 67pc for the herd.

However, conception rate and non-return rate are not the same thing -- conception rate can only be determined from confirmed pregnancy.

Unfortunately, the absence of heat doesn't necessarily mean that a cow is pregnant. So after insemination a cow is either:

• Pregnant and does not come back on heat -- on average about 53pc of cows;

• Not pregnant and cycles 18-24 days later, and is served (determines NRR);

• Not pregnant and cycles 18-24 days later, but the heat is missed;

• Not pregnant and cycles 18-24 days later, but expresses no or weak signs of heat;

• Not pregnant and does not cycle;

• Pregnant but loses the embryo and may come back into heat after four weeks.

These points mean that the conception rate is always lower than the non-return rate.

Generally, it works out at minus 10pc. So a non-return rate of 65-75pc would indicate a good conception rate of 55-65pc.

If the NRR is less than 64pc it may provide an early warning of a poor conception rate.

If you are concerned, the best way to confirm pregnancy is by scanning 14-16 weeks after the start of mating.

Scanning has the added bonus of determining your in-calf rate, calving spread and actual conception rate to help you plan towards next year.

Farmers often AI for six weeks before releasing a number of bulls into herds. First and foremost, make sure you have sufficient bull power.

There must be at least one bull for every 30 non-pregnant cows. Try to ensure that you have two sexually active bulls running with the herd.

Swapping them in and out of the herd every few days will help maintain their interest in the job at hand. Avoid bulls entering the collecting yard to reduce the risk of lameness and injury. Don't be afraid to use paint or other means to identify them easily.

Use bulls that are fertile and healthy -- sperm takes two months to produce, so an incident of high temperature associated with fever or heat stress can cause major disturbance in sperm production. Finally, look after yourself! A number of accidents on farms are associated with breeding bulls so make safety a priority.

Dr Mary Kinston is a Kerry-based farm consultant. Email: mary.kinston@gmail.com

Indo Farming