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Selecting Bulls for Heifer's

We are often asked for guidance in the selection of bulls suitable for use over heifers i.e. easy-calving bulls. Whilst recognizing that management plays a pivotal role in the easy-calving of heifers, genetics plays an important part also. Look for +ve [positive] calving-ease EBVs, both DIRECT and DAUGHTERS in the pedigree. Note that you don't necessarily have to sacrifice growth to achieve this.

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Multiple Joining - Some Issues to Consider.

For people who are worried about possible bull infertility or who, by virtue of paddock/mob sizes, need to run two or more bulls with a mob of females, there are a number of issues to consider.

  1. Two or more bulls running together always develop a peck-order of dominance. Sometimes this remains stable for months and at other times the status quo is under continuous challenge. In these cases fighting occurs regularly and leg injury may occur. Research shows that the dominant bull will sire the most calves in a multiple joining situation. Broken penises often occur when bulls get knocked from the side [as often occurs] when mounting a cow on heat.
  2. Cows and heifers cycle approximately every 20 days i.e. in a mob of open females you can expect 5% [1 in 20] to be on heat EACH DAY during the first cycle [3 weeks]. Therefore in a mob of 100 cows/heifers this means 5 per day, which is sufficient to keep 2 - 3 bulls occupied. i.e. minimal problems are evident at this stage.
  3. In both natural mating and AI, the conception rate on average is 67% i.e. two thirds of cows [67 in a 100 cow mob] will become pregnant and one third [33] will return to heat in three weeks time.
  4. In a 100 cow/heifer mob, this means that from weeks 4 to 6 only 1 - 2 cows will be on heat each day and bull competition/fighting will be intense. This is a key time for bull injury to occur. Again two thirds of cows/heifers on heat will conceive with approximately 22 of the 33 not conceiving in the first cycle getting in calf. Eleven cows remain to re-cycle over the next three weeks [i.e. during weeks 7 - 9 of the joining period].
  5. During this third cycle in a 100-cow mob, one of the non-pregnant cows will come on heat on average every second day. If more than one bull is with the mob, there is a huge risk of injury both from fighting and during attempts by any bull to mate with this cow on heat. It is better to remove all but one bull from the mob at this stage. To avoid any potential bull infertility effects, you can put a fresh bull with the mob each 1 - 2 weeks, removing the existing bull at the same time. Continue this pattern until all bulls are removed for the best of both worlds. [i.e. high fertility and low injury.]

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