A guide to Beef Shorthorn Selection Indexes
By Carey Coombs, Beef Shorthorn Cattle Society Director
The Beef Shorthorn Cattle Society now provides three Selection Indexes through its performance recording provider, Breedplan. A Maternal Index has joined the Self-Replacing and the Terminal Index, both of which have been updated.
Carey Coombs
It is important to appreciate that the Maternal Index is not a simple evaluation of traits that might be considered maternal traits. These traits are best evaluated as individual EBVs. The Maternal Index is an overall evaluation of genetic merit of an animal managed in a production system where maternal traits are of particular importance, but not to the exclusion of other important measurable traits.
What is a Selection Index?
Breedplan calculates Estimated Breeding Values (EBVs) for a range of economically importantly traits. While this provides cattle producers with a comprehensive range of information regarding the genetic merit of an animal, it can result in a dilemma when trying to select animals for use in a particular breeding program. In an ideal situation, it would be desirable to select animals that excel in all traits, but rarely will an animal be superior for all the available EBVs.
So which traits should producers put most emphasis on? How much emphasis should be placed on each trait? BreedObject is a tool that can help solve this dilemma. BreedObject combines the Breedplan EBVs for an animal with an economic weighting based on costs of production and returns on outputs, to produce a single Selection Index. A separate Selection Index can be produced for any particular production scenario and market. Selection Indexes enable cattle producers to make ‘balanced’ selection decisions, taking into account the relevant growth, carcase and fertility attributes of each animal to identify the animal that is most profitable
for their particular commercial enterprise. Selection Indexes reflect both the short term profit generated by a sire through the sale of his progeny, and the longer term profit generated by his daughters in a self-replacing cow herd.
Using Selection Indexes
As a guide to using Selection Indexes, it is recommended that producers complete the following steps:
Identify the Selection Index of most relevance to your production system
Rank animals on the Selection Index
Consider the individual EBVs of importance
Consider other traits of importance
It is important for producers to remember that cattle can attain similar index values through different EBV values.
For example, if a bull is selected using the Maternal Index, and Calving Ease Direct is of particular importance in your management system, for example to be used over heifers, be sure to check the individual EBV, as a bull may have compensated for having poor Calving Ease Direct by being exceptional in other traits, for example Days to Calving.
Please note
The Maternal Index, in particular, places a high emphasis on fertility. This is measured by the Days to Calving EBV. This is the only EBV that collects calving regularity data. Until more herds record this data then the spread between the highest and lowest maternal value indexes will be small. We would therefore encourage all breeders to collect the necessary data on an ongoing basis. Forms for collecting this data will be available from July 2019 onward. Back data from previous years can also be collected and analysed.
The Terminal and the Self-Replacing Indexes have been updated. Breeders will notice that animals have new index values and there will be some changes to the previous rankings.
Interpreting Selection Indexes
The Selection Index value for an animal is effectively an EBV of the animal’s profitability in that particular commercial production scenario and market. Ranking seedstock animals on their Selection Index value sorts them based on their progeny’s expected profitability for the targeted production system.
Selection Indexes are expressed as ‘net profit per cow mated’. For example, if we compare a bull with an Index of +£60 with a bull that has an Index of +£30, we can estimate that the difference in net profit from the progeny of the bulls would be :
= 1⁄2 x difference in Index
= 1⁄2 x (60-30)
= £15 per cow mated
NB. We need to multiply by 1⁄2 because only half the progeny’s genes come from the sire. If the two bulls were joined to 200 cows during their breeding life, this would equate to a difference of 200 x £15 = £3,000.
