Think heifers when ordering straws

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Dairy farmers are being encouraged to think differently when ordering artificial insemination (AI) straws this season: for every heifer replacement needed in the herd, order six straws.

While the obvious question most people ask is ‘how many to order?’ the more important question is ‘how many replacements do I need in three years time?’, according to the Australian Dairy Herd Improvement Scheme (ADHIS) and Dairy Australia’s InCalf project.

Michelle Axford, from the ADHIS, said that in the short term, AI straws are the key to getting cows in calf. But the real value of AI straws is the genetic merit of the heifers when they enter the milking herd.

“Decisions on semen selection today affect the genetic merit of the herd in years to come. We encourage farmers to select bulls from the Good Bulls Guide which meet their breeding objective,” Mrs Axford said.

In reviewing the number of replacements required, InCalf’s Barry Zimmermann suggests farmers look three years ahead and decide how many replacement heifers they’ll need entering the herd. “The number should include any extra heifers to expand the herd size or for sale or export,” Dr Zimmermann said. “Then it’s just a simple rule of thumb – allow six straws for every replacement heifer,” he said.

For example, a 400 cow herd with a 25% replacement rate, will need 100 heifer replacements every year, so 600 AI straws should be ordered to maintain the herd size. This rule of thumb allows for a 50% conception rate, 10% loss of cows prior to calving (eg. pregnant cows that are culled for other reasons), 50% female calves, 5% loss of heifer calves prior to weaning, 5% loss of heifers prior to joining, 90% heifer conception rate, 3% losses prior to calving (deaths, slips) and 3% heifers exiting the herd in the first 30 days post calving. “This approach helps you think about where you want the herd to be in three years time and ensures you’ll have enough replacement heifers without scratching around at the last minute buying extras,” Dr Zimmermann said.

The ADHIS website will soon have a simple calculator tool that allows the user to change the percentage rates of the various allowances for their herd. For more information visit www.adhis.com.au or contact ADHIS ph (03) 8621-4240. ADHIS is an initiative of Australian Dairy Farmers’, with most of its funding coming from Dairy Australia through the Dairy Services Levy. InCalf is Dairy Australia’s extension project to help dairy farmers improve the fertility of their herds.