British Simmental Indices

The Society is pleased to release a second selection index – the Self Replacing Index - to complement the Terminal Sire index. Selection indices integrate EBVs with costs and returns of production while focusing on meeting market specifications. The whole production system is considered – not just the sale animal. Feed costs are considered throughout the production system while accounting for costs and returns. The Society now has two selection indices which are focused on different sections of the industry – terminal sire production systems and self replacing herds. The indices will help you select animals suited to your production system and market requirements. The indices are independent, although some animals may rank well for both indices.

Terminal Index
The BSCS Terminal index is aimed at a commercial herd using Simmental bulls over large framed, mixed breed cows to breed steers and heifers to turn off at 16 months of age. All progeny are destined for slaughter and no replacement females are selected from within the herd. There is some emphasis on calving ease while finishing steers at around 630 kg live weight (335 kg carcase weight) using a pasture based production system supplemented with extra rations during the finishing phase.

Use this index in a commercial herd to produce progeny for slaughter. The index has moderate emphasis on easier calving (ie getting a live calf with minimal human interference) while producing calves that will then grow quickly to market specifications at around 16 months of age. The index is focused on slaughter animals and does not account for maternal traits and is therefore not suited to breeding replacement females.

If you are using smaller framed cows or heifers in your herd, then you should also put extra emphasis on a higher calving ease direct EBV when selecting a sire using this index.

Self Replacing Index
The BSCS Self Replacing index is aimed at a Simmental herd selecting replacement females from within the herd while breeding steers and excess heifers to turn off at 16 months of age. There is emphasis on calving ease and maternal traits while also looking to finish steers for slaughter at around 680 kg live weight (350 kg carcase weight) using a pasture based production system supplemented with extra rations during the finishing phase.

This Self Replacing index is also suitable to using Simmental sires over mixed breed cows where replacement females are sourced from within the herd. There may be some hybrid vigour expressed in the progeny depending on the breed type of the cows used. Therefore you should consider placing extra emphasis on the Calving Ease EBVs (more positive) of the sire to allow for possible heavier birth weights of his calves due to hybrid vigour.

Use this index in both commercial and pedigree herds where you are balancing the requirements of selecting replacement females while also producing animals for slaughter.

Calving Ease, Growth and Mature Size
Any selection index is trying to balance costs and returns. Calving problems are seen as a cost (man hours supervising during the calving period, assisting cows while calving, etc; calf and cow losses; lower production due to calving stress; potential re-breeding problems; etc). Growth and carcase attributes are return or income focused (although there is also a cost in feeding the animals, etc). Given that big animals at say 600 days of age were also likely to be big at birth (ie this is the “average” biology of cattle), then it is not surprising that both indices have a calving ease component. What can be surprising to some people is that an animal with a good index can still have a poor (low or negative) Calving Ease EBV. In such a case, this indicates that the costs of likely calving problems are more than compensated by the subsequent extra returns from the calves that are slaughtered. That is, you may not get as many calves and you may spend a lot of time getting them, but the ones you do get will knock your socks off.

The “average” biology of cattle also indicates that big calves tend to grow to be big adults; they will tend to eat a proportional amount of their body weight to maintain that weight which is critical when maintaining condition for mating and calving; and they tend to be older when they reach sexual maturity. Conversely, bigger cows tend to have less calving difficulties and have a better salvage value when culled than smaller ones.

The self replacing index is trying to balance all these traits using available information on genetics and economics to focus on profit.

Use the correct index
If you select replacement females from the calves you produce, you should use the Self Replacing index as your main index. The SR index does look at the maternal components as well as targeting the market requirements of the slaughtered animals. The Terminal index is just focused on getting a calf and then growing it out to market requirements. However, the indices are not mutually exclusive and some animals will have good values for both the Self Replacing and the Terminal indices.

Each index is a complete index in itself. The Self Replacing index is not like the old Calving Value. Calving Value attempted to just look at the calving component, whereas the Self Replacing index looks at calving, growth, carcase and fertility from both the direct and maternal perspective. That is, costs and returns are accumulated over the whole life of the animal, not just a small component of it. If you are looking at buying a cow, not only does she need to do the cow stuff (be fertile and have a calf each and every year, calve un-assisted, rear the calf to weaning, not be too expensive to maintain, etc.), but she needs to have the genes to give to her calves so that they will grow to market specifications and make a good profit – for whoever sells the calf to slaughter. That is, the index is based on the whole production chain.

Look at the Index, EBVs and Accuracies
The index is a means of weighting the relevant EBVs to focus on profit within the defined production system and market specifications. Therefore, the more information you have on the candidate animals (ie more accurate and more extensive range of EBVs), the better the potential ranking of these animals based on the index. Hence use the relevant index to give a broad ranking of animals, then look at the component EBVs (and accuracies) of the key traits in the index to fine tune your selection to animals that best suit your management and market requirements.

When using the index as an aid to buying replacement animals, also look at the key traits of the index and check that the herd selling the animals records the relevant traits. For example, if you focus on easier calving cattle, then ensure the selling herd routinely records calving ease and birth weights. For carcase traits, the selling herd should routinely scan all their animals (not just a couple of sale animals). Does the herd take scrotal measurements and weigh the cows when they weigh their calves for the 200 day weight? The quality of recording in the selling herd affects the quality of your decision in purchasing the animal.