For every heifer replacement needed in the herd, order six straws of semen to use this year.
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?’ 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. DataGene encourages farmers to select bulls from the Good Bulls Guide which meet their breeding objective. In reviewing the number of replacements required, farmers should 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. Then it’s just a simple rule of thumb – allow six straws for every replacement heifer. 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.
Find out how many straws you need for your farm? Download this simple calculator tool developed by InCalf and DataGene that allows the user to change the percentage rates of the various allowances for their herd.