Genetics

Understanding the long timeframes involved in genetic change in beef

Genetics editor Alastair Rayner, 07/09/2021

MAKING genetic change is a long-term undertaking in the beef industry. It is easy to appreciate the time associated with choosing a bull and seeing the resulting calves, but the longer-term changes are often more challenging to consider.

The timeline of impact a sire has on a herd has been highlighted previously in Beef Central genetics columns. A sire may directly influence 50 percent of the genes for steers born in his working life, and around eight age-groups of females, there is more to a herd’s make-up than this sire’s contribution.

It’s important not to overlook the point that a cow also contributes 50pc of a steer’s genetics, and 50pc pf her daughters that are retained in the herd.

The challenge for many producers is to consider what are the genetic influences at play in the cow herd? The following diagram outlines the genetic composition of typical self-replacing breeder herds. In a practical context, the calves born in 2022 will be able to attribute 87pc of their genetic composition to the last three generations of sires used in the herd.

Getting the impact from ‘game-changers’

One of the challenges for many producers is to understand why a new sire has not had the impact on a herd that may have been expected.

Often a new bull entering a program is seen as a game-changer. However, the calves that are born often don’t seem to live up to expectations.

Much of that outcome can be attributed to the influence of the previous sires. Their genetic influence, expressed in the cow herd, can be the reason why calves are a bit disappointing or the progress in changing is slower than expected.

Increasing rate of change

There are ways to work to increase the rate of change. One area to consider is the generational interval, or average cow age, of the herd.

Herds with predominately older cows allow the influence of previous sires to be expressed over a number of years. This can impact on the degree in which a producer’s efforts to correct or increase traits can be realised. It can be a long process to correct a trait when the traits of concern are deeply embedded across the herd.

Increasing replacement rate, lowering the cow age, will help reduce the timespan those cows can have to influence a herd. However, this can have its own challenges in terms of maintaining sufficient replacement females.

More importantly, increasing replacement rates can result in less selection pressure being placed on replacement females. Ideally genetic change occurs more swiftly in herds with lower generational intervals and high levels of selection pressure on replacements.

As this isn’t always an option for commercial herds, there are practical alternatives.

Selection pressure can be placed on replacements, and particularly on new sires.  Sires that are genetically superior should be used in preference to average sires.  These sires can be found using Breedplan data.

More rapid progress can come through joining these to the better groups of replacement females first and finding ways to reduce generational intervals by placing more selection on older cows. Some useful strategies have been to focus on fertility though restricted joining and to set production measures such as calves weaned and on weaning weights that are above herd average.

These practical measures can be combined to bring some pressure across the herd and open the way to make more genetic progress toward a herd that is productive and profitable.

 

Alastair Rayner is the Principal of RaynerAg, an agricultural advisory service based in NSW.  RaynerAg is affiliated with BJA Stock & Station Agents.  He regularly lists and sell cattle for clients as well attending bull sales to support client purchases.  Alastair provides pre-sale selections and classifications for seedstock producers in NSW, Qld and Victoria.  He can be contacted here or through his website www.raynerag.com.au

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Comments

  1. Matthew Della Gola, 08/09/2021

    I do agree with everything you are outlining here. But (and a polite but) I would also think that understanding your pedigrees and or bloodlines is extremely important. Probably more important to consider before anything you have discussed. Now this requires many hours visiting numerous herds of commercial or stud origin year after year; also following-up with once you’ve discovered the lines that suit your operation many hours following pedigree lineages to join those dots of those females that breed and breed and breed. Then once you’ve acquired this should you then look at ebv’s and god forbid “indexes”. The problem with a lot of inconsistent livestock is the splatter gun approach of populist breeding. Which folds in to quickly to many bloodlines of genetics which generally haven’t been given the time to mature over multiple generations. Unfortunately I don’t envy stud breeding as there is this constant urge to move on from proven genetics to soon.

    Thanks Matthew, you do raise some very important and valid points here. I was offering these observations for commercial producers who may not really consider, or need to consider the pedigrees across their herd. For most commercial producers, their breeding objectives should reflect suitability to their environment, and to their chosen market. Decisions to shape the direction of their herd should follow from the feedback their market provides and on the data they record on farm regarding the herd performance in that environment. I think in these cases its important to remember that a new sire / team of sires won’t make major changes in the first generation and for that to happen it requires that selection pressure and generation interval reduction as discussed. Genetics Editor

  2. Paul+D.+Butler, 08/09/2021

    Positive genetic change is entirely based on positive selection. Select for profitability not big computer fantasy numbers.

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