Are your replacement heifers on track for breeding?

Successfully breeding next year’s replacement heifers to calve down at two years of age starts with identifying heifer calves born on the farm this spring, Teagasc Beef Specialist, David Argue shares his key tips on heifer selection.

Select heifers born early in the calving season from your best cows that have plenty of milk and are sired by bulls that have good maternal traits. Research shows that if a heifer is born in the first three weeks of the calving season, she has a 25% greater chance of lasting to her 4^th lactation or beyond. In doing this, it will allow the heifer more time to grow and develop before she is required to start cycling.  

Heifers should be 275kg to 300kg at weaning, which means they will need to gain a minimum of between 60kg to 75kg over their first winter indoors if you want them to reach the target weight of between 335kg to 375kg at turnout the following spring. Where possible, group these replacements together for the first winter for priority treatment. If average daily gain is poor, supplementary concentrates may need to be introduced to achieve target growth rates. This could mean feeding 2kg - 3kg of concentrates depending on silage quality in order to achieve the target 0.6kg gain/day over the winter.

Table 1 below shows some of the key target weights needed at the various stages for 24-month-old calving.

Table 1: Growth targets for replacement heifers calving at 24 months of age

Early turnout is essential for these replacement heifers if we require them to be 380kg-420kg (depending on breed) or 60% of the mature cow weight at breeding. From turnout to breeding, the heifers are required to put on 45kg-50kg of liveweight – provided they are on target to begin with.

It is important to remember when selecting these replacements heifers that they have the potential to grow into that 60% mature cow weight by 15 months. Where potential replacement heifers are lagging behind, are light for age or are compact in size, their ability to grow into a mature weight suitable for your individual system may be limited. Farmers’ preferences for cow weight and size differ, so for a more accurate estimate of your suitable cow size, examine your weighing reports from ICBF.

If the heifers are not heavy enough at breeding, this may result in them not cycling at the start of breeding. This, in turn, will lead to a delay in the calving date. Heifers that are too light at bulling more than likely will go in calf but they could struggle to go back in calf the following year while rearing a calf.

At the end of the second grazing season, these heifers need to be between 540kg and 570kg to allow them to calve down at the desirable weight. It is important to weigh these heifers regularly at each stage of their life to ensure they are hitting their target weights. Weighing will allow you act in good time if animals are behind target and avoid trying to play ‘catch up’ when it is too late into pregnancy. Good quality grass and access to clean after grass later in the year will aid in achieving these weights.

Bull selection

Careful selection is needed when picking a suitable bull for the heifers. Use a well proven bull that has a low calving difficulty percentage (4% or less) with a high reliability figure. In some cases, it is safer to use AI on these heifers as the reliability figure tends to be much higher than that of a stock bull. A small live calf is all that is required of these heifers to calf down at two years to make them more profitable than heifers calving down at three years, so attention needs to be paid when picking a bull.

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