19 April 1996

in SACstyle

Replacement,

Suckler producers thinking of using home-bred replacement heifers after the latest BSEscare have several options to consider. Jeremy Hunt, Jonathan Riley and Sue Rider report

HEIFER replacements at the Scottish Agricultural College are now being bred from its suckler herd using a criss-cross breeding system.

SAC beef specialist Basil Lowman explains that it was becoming difficult to find sufficient Hereford x Holstein bulling heifers as replacements for the 160-cow spring-calving herd at the SACs Bush Estate, Penicuik, Edinburgh.

Even the Limousin x Holstein replacements were difficult to source and increasingly expensive.

Justification for the switch to using home-bred replacements in March last year was partly due, therefore, to the high price of heifers in the marketplace. But the decision was aided by the advent of best linear unbiased predictions (BLUP) and estimated breeding values (EBVs). These tools made it easier to select bulls to breed good heifer replacements. So having examined the options available. Dr Lowman opted for a criss-cross breeding system to supply replacements. This allows hybrid vigour, so important for fertility, says Dr Lowman.

It uses two beef breeds to produce a cross-bred cow. Heifers sired by one breed are mated to the other breed, and their daughters back to the original breed.

Because some of the SAC farm is an upland unit, Dr Lowman opted for a medium sized cross-bred cow with the ability to eat a lot of grass and lay down fat to minimisewinter feed costs.

"We decided to use an Aberdeen-Angus x Limousin, to produce this medium sized cow." Dr Lowman hopes the Limousin will stretch cow size and put improved conformation into the steer. But he admits milkiness is a risk in this cross. He therefore selects Angus and Limousin bulls for breeding replacements on 200-day milk EBVs.

The second cross the SAC is looking at is for the lower ground on the farm which would carry a bigger cow. Here, Dr Lowman has chosen a pure Continental cross cow – a Simmental x Limousin. For milkiness the cross depends on the Simmental but Dr Lowman is protecting milking ability again by selecting sires on the basis of their EBVs for 200-day milk.

Dr Lowman is using the Limousin to hold down the size of the Simmental while helping to improve conformation.

Types of cattle Dr Lowman would never consider as replacement sires are the Charolais due to its large size and poor milk production and the Belgian Blue, which is potentially a difficult calving sire.

When deciding which cows to breed heifer replacements from, Dr Lowman would ideally select cows which had performed best on his unit. However, he is not doing that on the SAC farm. Instead he is trying to measure the financial benefit of using top AI bulls selected on EBVs for growth and milk value.

He has synchronised all cows seen on heat on day one of the mating period using the best Angus, Limousin, and Simmental AI bulls to produce heifer replacements, and then sweeping up with Charolais bulls.

His priority is to secure the very best bulls available and to be able to change those year by year. He recognises that one of the snags with using home-bred heifer replacements when using bulls, and only one or two of them, is that in a couple of years time the bull is back on his grand-daughters. There is a need to change bulls and that increases costs.

Another advantage of using AI and oestrus synchronisation to produce heifer replacements is that they will be born early in the calving season.

As such they should be two-years old when they themselves calve but still calve early in the calving season. That is essential to maintain a tight two-month calving pattern.

If, however, he selected a heifer from his very best cow which calved three weeks after the start of calving, if that heifer was to calve down in the first week in two years time, she would only be 21-months old. That, says Dr Lowman is too young.

Finally, he suggests anyone considering breeding their own heifer replacements, should be able to answer the following: "What cows will I be mating to what bulls in 10 years time." The breeding system must be sustainable.

Dr Lowman knows exactly what cows will be mating to which bulls in 10 years time. Take the Limousin x Angus herd. All his Angus sired heifers will be mated to Limousin bulls, and all Limousin sired heifers and cows are mated to Angus bulls.


&#8226 Cross-bred cow for its hybrid vigour.

&#8226 Select on EBVs for milking ability.

&#8226 Avoid Charolais and Belgian Blue sires.

&#8226 Use of AI and heat synchronisation.


HOME REPLACEMENTS

Simmental x Holstein Friesian heifers with Limousin calves at foot at the SAC.Dr Basil Lowman will keep the heifer calves as replacements. In two years they will calve to Simmentals.