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Wet weather is increasing the workload as the mating period moves into top gear

April has certainly had its challenges and unfortunately recent weather forecasts don't give any real hope of light at the end of the tunnel.

Generally low grass growth rates have been the major concern, with the risk of low and falling averages for grass cover.

This has been compensated for by feeding extra meal and standing silage crops or baled/pit silage while holding a longer rotation, such as 25 days.

For some, this has been coupled with high rainfall and deteriorating ground conditions, which have eventually resulted in the final step of putting the cows in for a few hours at night or even a few days.

Tired faces and gloomy outlooks have been noticeable at discussion groups due to the extra workload of the last few weeks, and this is now coming on top of mating maiden heifers and cows.

The reality is that while many may breathe a sigh of relief at the end of calving, the mating period is actually the busiest time of year.

Options for mating heifers have been discussed on many occasions, but, with pressure mounting on other fronts, many farmers have opted to PG (synchronise) heifers after a week of AI to speed up the process.

Synchronising heifers allows them to be moved off the milking platform and reduces the workload as quickly as possible (after 12 days). Others are juggling their circumstances to cover the heifers with AI for three weeks.

Body condition score has also held up for many herds, having generally been slightly better at calving than previous years.

Breeding options for the cows have been discussed, including how long the cows will be mated with dairy AI. Many farmers are seeing the opportunity to use these progeny to increase milking cow numbers post quota in 2015.

Using AI for six to nine weeks is common practice. When deciding how long to use dairy AI straws for, the obvious question to consider is how many AI-bred replacement heifers do you want?

Cost must also be a consideration, given the potential for a significant fall in milk price.

The percentage of AI replacements is determined from the percentage of replacements required to cover the losses of empty cows and voluntary culls, plus the percentage of heifers required for increased cow numbers or for dairy stock sales.

Table 1 outlines the potential percentage of replacements that would be generated with varying fertility (submission and conception rates) for a dairy sire AI mating period of either three, six, nine or 12 weeks, with 50pc ratio of bulls to heifers and 15pc loss due to mortality or failing to go in-calf.

A farmer with 100 cows, AI mating for six weeks with a herd of average fertility, will generate around 29 heifer calves as long as the bull-to-heifer ratio does not exceed 50pc.

If the herd had a 15pc empty rate and voluntary cull of 3pc reducing cow numbers by 18, the example above would result in 11 extra heifers (29-18).

Farmers wishing to increase the herd by 50pc in five years would require an extra 8.5pc of replacement heifers over and above the number required to simply replace cull cows.

For those using AI on maiden heifers for three weeks, or achieving a submission and conception rate of 90pc and 65pc respectively through synchrony, additional heifer replacement can undoubtedly be secured.

If holding a 30pc replacement rate (e.g. 30 maiden heifers and 100 cows), this will potentially provide for only an extra seven AI-bred heifers for the herd.

It is a given that AI on maiden heifers speeds up the potential genetic gain of the herd.

However, if this genetic gain is being delivered at a high cost to labour and pasture cover, consider other options.

For the cows, consider what AI time frame suits your system best.

Later born dairy heifers will generally be smaller and require segregation and preferential feeding to hit your target liveweights at breeding.

Dr Mary Kinston is an agricultural consultant based in Kerry. Email:

Indo Farming