Purpose of an Index


By Lance Bauer, Director of Breed Improvement & Western Field Representative

In previous articles I have mentioned that the purpose of the seedstock industry is to continually advance and make animals that fit into the commercial industry and make them more profitable. I have also mentioned the tools that are available to producers to help them make informed breeding decisions that should lead to increased returns. A key component to informed decisions is that a producer should never select on just one criterion, in other words avoid single trait selection. When looking at Expected Progeny Differences (EPDs) it can sometimes be difficult to avoid single trait selection because a producer may become too focused on one trait, such as birth weight. To help producers avoid this, many breeds including Beefmaster, have implemented one or more indices that weight EPDs appropriately for different production systems. The use of index selection has been around since the 1940s. In 1943 Hazel noted that using an index that was properly weighted was more efficient than single trait selection or culling based on several traits with an individual culling level for each trait. In summer 2016, BBU released two indices, $M and $T, to help producers select animals that fit their production systems. $M is the maternal index and should be used when females are being retained in the herd. $T is the terminal index for BBU and should be used in a terminal production system.

$M is the maternal index and it is designed to balance weaning weight with cow maintenance and fertility. The index includes the EPDs for birth weight (BW), weaning weight (WW), Milk, yearling weight (YW) and scrotal circumference (SC). It was developed for the profit per cow exposed, due to the weaning weight of her calf and accounting for cow maintenance. $M is helpful in evaluating how a bull’s daughters will contribute to the advancement of a herd. When looking at Beefmaster cattle $M seems like a smaller number than $T, however the effects of $M are cumulative because of retaining females in the herd. A bull that consistently produces high quality females that are kept in the herd is continually increasing in value to the producer in terms of $M.

For example, if a producer is looking to use a bull that will produce quality females that will wean a good calf every year and they are choosing between two bulls, then $M is a good tool. If Bull A has a $M of 24.50 and Bull B has a $M of 14.50, then it would be expected that Bull A’s daughters would return approximately $10 more per head per year. This may seem to be a small amount, but if we assume that both bulls are bred to 20 cows and 10 heifers are retained each year, then after a year there is a $100 advantage for Bull A. If both bulls are used for four years with the same results on keeping heifers, then there is a $400 advantage to Bull A. Now assume that each of the heifers that is kept stays in the herd for 10 calves, now there is a $4,000 advantage to Bull A. This is a value that could be increased by using reproductive techniques, such as artificial insemination or embryo transfer, to produce even more females from a valuable bull.

$T is the terminal index and is designed to be used when bulls are mated to cows in a strictly terminal system, in other words all offspring will be harvested. The EPDs that are used in the calculation of $T are YW, rib-eye area (REA), intramuscular fat (IMF) and Fat. The goal of this index is to help the producer select and use bulls that will produce high quality carcasses that also yield well and will help make the operation more profitable. By comparing $T of different bulls a producer can estimate how much more a bull could potentially be worth in a terminal system.

For example, if a producer is selecting a bull to produce calves that will do well in a feedyard and they are choosing between two bulls, then $T would be an informative tool to use. If Bull X has a $T of 100 and Bull Y has a $T of 60, it would be expected that Bull X’s calves would be $40 more valuable per head on average. In this situation if both bulls are used on 20 cows and you produce 20 calves, then after one-year Bull X is worth $800 more than Bull Y. If both bulls are used for four years in the herd with the same results, then Bull X becomes worth $3,200 more than Bull Y. This value could be even more if artificial insemination was used and more steer calves from Bull X were produced each year.

An index is another tool that producers can use to make informed breeding decisions that will help return the most profit to the operation. It is important to remember when using an index that a producer should have a production system in mind and then choose the appropriate index. Selection on an index is more efficient than single trait selection or setting culling levels for multiple traits because it is economically weighted for that production system. $M is the Beefmaster maternal index that is designed for a maternal system where replacement females will be kept and used in production. $T is designed as a terminal index to be used when all calves will be sold for harvest. There has been a great amount of research put into both indices and the economic values assigned to each trait. They are a great tool that can and should be used to help eliminate single trait selection. Remember to use each index for its intended purpose.

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