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South African Simbra Selection Indexes: Technical Specifications

More detailed information regarding each selection index is provided in the downloadable document.

The Simbra Cattle Breeders’ Society of South Africa currently reports three different selection indexes. These are the:

  • Self-Replacing Feedlot Index (SRF)
  • Self-Replacing Weaner Index (SRW)
  • Self-Replacing Grassfed Index (SRG)

All of the selection indexes described above have been derived using BreedObject software. The BreedObject selection index development process involves four major steps. These steps are:

  1. A detailed description of the input costs and value generation of the commercial herd and target production system.
  2. Once the target production system is described, the BreedObject software evaluates how each trait influences profitability and the economic value of improving each trait.
  3. The BreedObject software then assesses what emphasis needs to be applied to each Estimated Breeding Value (EBV) trait to achieve the maximum profitability in the production system and for the market end point for which that index was designed. This step includes evaluating the selection response expected from direct selection on the individual EBVs and the correlated responses expected from selection on related EBVs.
  4. The importance placed on each EBV results in the selection index value that is calculated for each animal.

Each selection index describes a different production system/market scenario and relates to a typical commercial herd using Simbra bulls. As is the case for EBVs, each selection index can be used to rank and compare animals on their genetic merit. Producers are advised to use the selection index that most closely aligns to their production system. See the Using South African Simbra Selection Indexes tip sheet, available in the Help Centre on the BREEDPLAN website, for further information on the identification and utilisation of the most applicable selection index for your herd.

All selection indexes are reported in units of net profitability per cow mated (Rand) for the production system/market scenario they describe. Selection indexes account for both sides of the profit equation (costs as well as income), and also reflect the relative short and long term profit associated with possible selection decisions. For example, short term profit can be generated by a bull through the sale of his progeny, and the longer term profit generated by his daughters in a self-replacing cow herd.

Each of the selection indexes are focused on efficient beef production while also targeting the following specifications:

Self-Replacing Feedlot Index (SRF) - Estimates the genetic differences between animals in net profitability per cow joined for a herd that keeps replacement females and requires a moderate emphasis on calving ease. Progeny age at turnoff is 14/15 months after 120/150 days of extra feed. Steers target 510 kg live weight (275 kg carcase weight) and heifers target 445 kg (260 kg carcase weight). Emphasis was placed on carcase quality.

Self-Replacing Weaner Index (SRW) - Estimates the genetic differences between animals in net profitability per cow joined for a herd that retains replacement females while excess progeny are sold at weaning. Use this index in conjunction with the self-replacing feedlot index to maximize selection pressure on your replacement females while targeting the feedlot sector endpoint for excess progeny. Significant emphasis is placed on calving ease, 200 day weight, days to calving and carcase yield while moderating mature cow weight.

Self-Replacing Grassfed Index (SRG) - Estimates the genetic differences between animals in net profitability per cow joined for a herd that keeps replacement females and requires a moderate emphasis on calving ease. Progeny age at turnoff is 23 months off pasture. Steers are around 500 kg live weight (260 kg carcase). Emphasis is placed on carcase quality.

More detailed information regarding each selection index is provided in the downloadable document.

If you have any further queries regarding the South African Simbra Selection Indexes, please do not hesitate to contact staff at the Simbra Cattle Breeders’ Society of South Africa.