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All cattle breeders will agree that selection indexes are the preferred way to simultaneously select for multiple traits that affect herd profitability. The number of traits is ever increasing, so ready-made selection indexes offer a solid solution to wrap important traits into one value that can be used to rank and compare animals. This relieves producers from having to remember all the intricate trait details, such as how all traits genetically correlate.
However, selection indexes also make for great marketing tools. What is better than one single selection value for herd profitability? As companies are looking for ways to differentiate, the number of different proprietary traits, different indexes and proprietary traits within indices grows.
While selection indexes exist to make selection on many traits easier, we are now faced with the challenge of what to do with the many available indexes.
The variety of indexes is driven by the fact that there is no golden ticket to herd profitability. Selection objectives differ between producers based on the strengths and weaknesses of the herd as well as milk checks and geographical locations. There is literally no one-size-fits-all solution. Yet, all producers want to increase income and lower cost – and every company, country or breed association has an opinion on how to achieve that.
So, when every index claims to be the ticket to success, how do you choose the one that fits you best?
What is a selection index?
Index selection is a tool for improving traits simultaneously while accounting for correlations between the traits. All individual traits are weighted based on their importance and their probability of improvement. Through index selection, a breeder in essence creates a single new trait, the “index,” which is then used to compare animals for selection and mating.
To construct a proper and mathematically sound selection index, one needs quite a few components.
First and most importantly, you must know what you want to improve. What is the breeding goal? Lifetime profitability is an example. Then you must decide on the traits that go into the index to achieve the breeding goal (e.g., milk yield, daughter pregnancy rate, body size, calving ease, etc.).
The complicated part lies in all the relationships that must be considered to minimize risk of unintended response to selection. To correctly weigh all traits, you need to consider all the phenotypic and genetic correlations that may exist.
And finally, you need the weightings that decide the contribution or "importance" of each trait to the final breeding goal. These can either be economic weights or preference weights, but regardless, they are often the point of discussion when indexes are developed or updated.
Know what you need: Define your breeding goal
It sounds cliche, but it is fundamentally important to establish a long-term breeding goal. This can be done with the help of advisers but should be done based on herd and cow data and producer ambitions and be independent of what anyone may be trying to sell.
Knowing what your herd needs to achieve higher profitability is the first step to choosing or building a selection index. In that exercise, it is important to differentiate what your herd needs from the genetics that you may want. The latter is often influenced by marketing, and while there is nothing wrong with that, it has very little to do with choosing a selection index for the genetic improvement of your herd.
Understand that high ranking does not always mean better
A breeding goal cannot simply be a desire to use the best bulls in your mating program. Your herd and business should dictate your strategy. It is easy to simply use the highest bulls on a ranking list, and there is business value in that as well. But that does not mean that those bulls are the best for your herd.
As stated earlier, selection indexes were developed to give breeders an easy and reliable way to rank and compare animals for selection toward their breeding goal. Can the Total Performance Index (TPI) or the Jersey Performance Index (JPI) fit your breeding goal the best of all indexes out there? Absolutely, especially if you are a Holstein or Jersey breeder. However, the large popularity of these indexes imply that they suit the breeding goal of most herds perfectly, and that is unlikely.
It is perfectly possible – in fact, it is quite likely – that a middle-ranking bull fits a large group of producers better than the No. 1 bull in that list.
We cannot ignore that it is the competitiveness and business value of the highest bull that drives the popularity of these selection indexes. It is, to a large extent, the fear of missing out that creates the selection of high-ranking bulls, not the fact that the index nailed the breeding goals of all these herds. This is a very prevalent trend that gets in the way of fitting the appropriate genetics to a herd for proper genetic improvement.
