Farm Ireland

Saturday 16 December 2017

Poorer submission rates force a rethink on bull calculations to guarantee cows calve next spring

Mary Kinston

The sun has been shining bright in the sky, soil temperatures have risen above 15°C and with the distant rumble of silage harvesting, I think we can finally say summer has arrived.

While we in the west are loving this dry sunny weather and praying it will continue, I know that there will be others wishing for some rain.

It is easy to assume that the weather issues facing all farmers are similar but it's hard to believe the extremes of variation between farms.

In recent weeks we have had some farms where tractors would get stuck and others where farmers could drive a full articulated trailer of silage over the land.

This spell of dry weather has eased farmers' workload considerably. Break wires have been removed from paddocks and animals have stopped the aimless walking that's done in wet conditions.

There is now a degree of flexibility in when jobs can be done, with ground conditions allowing slurry and fertiliser spreading, silage cutting, pre-mowing and topping to be done with ease.

It won't be long until the bulls are put in with the cows, which will also ease the workload further. Most farmers opt to use bulls for around six to eight weeks of mating.

However, submission rates have been lower than desired this year for a number of herds, with 70-80pc submitted a common result after 21 days.

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Bearing this in mind, and to ensure good in-calf rates during the natural mating period, it's imperative that when AI is ceased, enough bulls are put into the cows.

To calculate the number of bulls that you need to run with your herd depends on the estimated number of non-pregnant cows that you will have at the end of the AI period.

At least one bull is required for every 30 non-pregnant cows in the paddock, with additional bulls required to allow for regular bull rotations and to replace bulls that become inactive or unhealthy due to problems such as lameness.


Your estimated bull number is calculated using your three-week submission rate, an estimated conception rate and the number weeks that AI has been used for.

The table shows estimates of the required bull numbers for varying herd size, submission rate and AI period, assuming a conception rate of 50pc.

Always round numbers up to the next whole number, for example, 1.4 requires two bulls.

Also a 'half resting, half working' bull rotation policy will require double the number of bulls shown in the table.

For example if you have 100 cows and a submission rate of 72pc after six weeks of AI, you would require three bulls to run with the cows (1.4 x 2), with two bulls in the paddock at all times.

In comparison, if your submission rate had been higher at 92pc, then you would only require two bulls (1.0 x 2), with one bull in the paddock at all times.

If you haven't enough bulls, consider the use of AI for longer.


Another job that must take priority is the regular dosing of weanlings, which can easily be forgotten.

With the ill-effects of 2012 showing its impact on yearling heifers, it is imperative that we remain focused on parasite management and the growth of the weanlings this year.

Finally, June summer conditions coincide with the grass plants' desire to head out and in many paddocks there is elongation of the seed head of both perennial ryegrass and other undesirable grass species.

Maintaining good pasture quality to provide a high quality diet for cows will be an uphill struggle for the next few months but it's an essential task to complete to maximise milk output and ensure successful mating through a rising plane of nutrition.

Strategic closing of paddocks for bales or the pit, and the use of pre-cutting or topping will be necessary where seed heads are evident.

However, use these tools with caution, especially where ground conditions are becoming dry, as cutting will impact on grass growth.

If using pre-cutting prior to grazing, alternate this with paddocks that will be grazed without cutting to minimise any ill-effects on the cows in terms of diet quality and intake.

Mary Kinston is a discussion group facilitator and consultant, and farms with her husband in Kerry. Email:

Irish Independent