The bull sale season is just about upon us and it is important to understand and appreciate the genetic selection information that will be provided on many Brahman Bulls this season. A very powerful selection tool for commercial and seedstock producers alike are the Brahman Selection Indexes.
A Selection Index is effectively a single unit value predicting a breeding animal’s profitability for a defined commercial production system and market end-point. They are based on weightings on specific EBV traits deemed important for that production system. Ranking animals on their Selection Index value sorts them based on their progeny’s expected profitability for the targeted production system.
As a guide to using Selection Indexes, it is recommended that producers, both seedstock and commercial, undertake the following steps:
- (i) Identify the Selection Index of most relevance
- (ii) Rank animals on the Selection Index
- (iii) Consider the individual EBVs of importance
- (iv) Consider other traits of importance that may not be accounted for in the Selection Index (e.g. temperament, structural soundness)
1. IDENTIFY THE SELECTION INDEX
As mentioned above, a Selection Index value for an animal is effectively a single unit value predicting an animal’s profitability for a defined commercial production system and market end-point. Consequently, before using Selection Indexes, producers should identify the index that is of most relevance to their particular production system. For seedstock producers, this may be the production system of their bull buying clients. In order to identify the most relevant Selection Index for use, it is recommended that producers consider the description of each Selection Index available. Following are the descriptions for the 2 Brahman Selection Indexes:
Jap Ox Index – The Jap Ox Index estimates the genetic differences between animals in net profitability per cow joined for an example commercial herd targeting pasture finished steers for export markets. Steers are assumed to be pasture grown & finished, weighing 600 kg live weight or 325 kg carcase weight at 32 months from a self-replacing herd run in a tropical environment. Daughters are retained in the industry for breeding. This Jap Ox Index relates to typical self-replacing Brahman herds in tropical Australia targeting Jap Ox specifications.
Live Export Index – The Live Export Index estimates genetic differences between animals in net profitability per cow joined for an example self replacing commercial herd (run in a tropical environment) targeting steers for the live export markets. This index assumes steers are pasture grown until entry to overseas feedlots and then feedlot finished for 120 days before being marketed at 470 kg liveweight (250 kg HSCW and 10 mm P8 fat depth) at 26 months of age. Daughters are retained for breeding.
Selection Indexes are developed for the commercial sector, as indicated by the descriptions above, therefore it should be relatively simple for a commercial producer to select one of the available Selection Indexes to use in their selection decisions. This is a slightly more complex task for seedstock producers as they are generally providing bulls to a range of commercial producers who are in a range of production systems and supplying a range of market end points. In this situation we recommend that Brahman seedstock producers use the Selection Index that suits the majority of their commercial clients and recognize that the Brahman Selection Indexes are highly correlated, therefore selecting on one (e.g. Jap Ox) will also generally lead to a positive trend for the others (e.g. Live Export).
2. RANK ANIMALS ON SELECTION INDEX
Once the Selection Index of most relevance has been identified, the animals available for selection can then be ranked on that particular Selection Index. An example of this is in figure 1, where the “Published Sires” list has been ranked in descending order on the Brahman Live Export using the Brahman online EBV Enquiry facility.
When ranking animals on the Selection Index, producers should also take into account the following points:
- Selection Indexes can not be used to compare animals across breeds. As with EBVs, the Selection Indexes for animals of different breeds are calculated within different BREEDPLAN evaluations.
- Consequently, Selection Indexes can only be used to compare animals with other animals of the same breed.
- Producers can use Selection Indexes to see where an animal ranks compared to other animals of the same breed by comparing its Selection Index value to the current breed average value and to the percentile table.
Comparing an animal with the current breed average Selection Index will give you an indication of how the animal compares with the current genetic level for the breed in terms of profitability for that particular production system and market scenario. The current breed average values are located on the last row in figure 1. If we consider the Live Export Index value of Lanes Creek Red Ranger (AI) (P) of +$57 and compare it to the breed average value, it indicates that this animal is expected to have genetics that are more profitable than the current genetic level of the breed if the animal is used within this production scenario.
Figure 1. Brahman Published sire list ranked in descending order on the Brahman Live Export Index
Comparison of an animal’s Selection Index value to the breed average can be taken a step further by looking at the Percentile Bands table to determine exactly where the animal ranks within the breeds. If we consider the animal in the above example with the Live Export Index value of +$57, the Percentile Table below indicates that the animal is in fact ranked in the top 1% of the breed for that particular production scenario and market endpoint (see circled information in figure 2.)
Figure 2. Brahman Percentile Bands for 2010 Born Calves
As with the breed average EBVs and Indexes, a Percentile Table should be enclosed in all BREEDPLAN reports, sale catalogues etc. They are also accessible from the BREEDPLAN website (http://breedplan.une.edu.au).
3. CONSIDER INDIVIDUAL EBVS OF IMPORTANCE
While Selection Indexes combine all the available EBV information to provide an indication of an animal’s overall genetic merit, it may still be important to pay attention to the animal’s individual EBVs for traits of particular importance. For example, producers may pay attention to:
Scrotal Size and Days To Calving EBVs if they want to specifically improving fertility in their herd Birth Weight if they are planning to use the bull over heifers Fat EBVs if they require more or less fat on their steers at slaughter In order to consider the animal’s individual EBVs, it is recommended that producers set maximum/minimum EBV ranges for the individual traits of particular importance. Animals should firstly be ranked on the Selection Index of relevance but then any animals whose individual EBVs fall outside of the acceptable range be excluded from selection.
4. CONSIDER OTHER TRAITS OF IMPORTANCE
While Selection Indexes take into account all the available performance information on an animal, they do not consider all the traits of functional and economic importance. Consequently, Selection Indexes should be used in association with assessment for other traits of importance that may not be accounted for in the Index (e.g. structural soundness, temperament) and Bull Breeding Soundness Evaluation information.
You can access further information on the Brahman Selection Indexes from the Brahman TBTS Technical Officer, Paul Williams, ph: 07 4927 6066, Mobile: 0427 018 982 or email: paul@tbts.une.edu.au or on the BREEDPLAN website (http://breedplan.une.edu.au)
BRAHMAN NEWS SEPTEMBER 2012 ISSUE #176
By Paul Williams TBTS TECHNICAL OFFICER
