Without these, it’s easy to forget to focus on economically important traits.
As a heifer has no proven record of reproduction, ease of calving or maternal ability, information relating to the mother, the father and other relatives should be used to make an informed decision at selection.
Breeding values are best
If available use breeding values rather than performance testing indices. Genetic merit is more reliably indicated by breeding values. Use it in balance with other important traits, especially those related to functional efficiency.
Selection: what to look for
First selection usually occurs when heifers are weaned.
Traits to be considered at this stage are:
Pre-weaning growth and milk production: The heifer’s weaning index reflects its mother’s milk production and its own growth rate to weaning. Cull heifers with a low weaning index (under 90), especially if their mothers have a record of weaning calves with poor weaning indices and/ or poor breeding values for weaning direct (pre-weaning growth) and/ or weaning maternal (milk production).
Ease of calving: Cull heifers with a small pelvic opening and with mothers who have a record of difficult calving.
Reproduction: Cull heifers with mothers that calved late for the first time, with a long inter-calving period or whose reproduction index is under 90.
Hereditary defects: Cull heifers with any hereditary defect, such as a skew face or undershot jaw.
Functional problems: Cull heifers with severe functional problems affecting the legs (such as straight hocks or sagging pasterns), hooves (outgrowing or deformed), skin and/or coat (long hair, a lack of skin pigment).
Frame size: Cull all heifers that are too large.
Hormonal imbalance: Cull heifers that lack femininity and/or have underdeveloped genitals (small vulva). This is evidence that there may be a hormonal problem.
Temperament: Cull heifers with difficult (wild) temperaments. Second selection usually occurs just before the heifers are bred at between 15 and 24 months. Inspect the heifers again for hereditary defects, functional problems, frame size, temperament problems and signs of hormonal imbalance.
Next, evaluate the following traits:
Pre-wean and post-wean growth: Cull heifers with a low (below 90) 12-month and/ or 18-month index. As both are calculated on growth from birth, these indices are a function of the mother’s milk production and the calf’s weaning and post-weaning growth ability.
Pelvic opening: To identify heifers that will probably have difficulty calving normally at an early stage, have their pelvic openings measured by a vet and cull those with small openings before the start of the breeding season. Easy calving in a first calver means that the uterus and birth canal will recover and return to normal faster and the animal will cycle sooner than an animal that had difficulty calving.
Selection by breeders’ society: If a breeders’ society is due to inspect the herd, the inspection will usually take place at this stage. The third selection occurs when pregnancy is diagnosed. All heifers that are not pregnant should be culled. If more pregnant females remain than are needed for replacement or building the herd, consider culling the heifers that became pregnant late in the breeding season and which will calve late in the calving season, as these cows are unlikely to re-conceive the following year.
The fourth selection takes place after calving. Cull all first-calf cows that had difficulty calving, if this was not due to other factors such as overfeeding shortly before calving.
The final selection occurs when the calves of first-calf cows are weaned.
Cull all cows with calves that have a low weaning index (under 90). Also cull first-calf cows with a low cow efficiency index (under 90).
This expresses the weaning weight (adjusted for age to 205 days) of a cow’s calf, compared with the cow’s metabolic or maintenance weight (weight to the power 0,75) at calving (or at weaning, if not recorded at calving).
For example, a 500kg cow weaning a 250kg calf is more effective than a 600kg cow with a calf weaning the same weight.
Leslie Bergh is a senior researcher with Beef Cattle Recording and Improvement, at the Agricultural Research Council’s Animal Production Institute in Irene.