MANAGING RECESSIVE TRAITS

CSPA BULLETIN

Management to Eliminate Inherited Recessive Traits

A Fact Sheet and Guide for Producers

The following pages break into two parts. 

PART ONE describes recessive traits and animals which are carriers and animals which are free.  The recessive traits under consideration are red coat colour, horns and double muscling.  If you are familiar with these details, please go directly to PART TWO. 

PART TWO discusses several strategies to manage these recessive traits in your herd.  Part Two begins on page five.

PART ONE.   Inherited Recessive Traits

What is a Recessive Trait?

Many physical traits can be linked directly to a specific genetic variant (mutation) in the DNA, and these variants can be passed from parent to offspring. Because an animal inherits a copy of DNA from each parent, a mutation can be transmitted from either the sire or the dam.

A “dominant” trait is one that is physically observable in an animal when it inherits only one copy from either its sire or dam. It only takes one copy of the mutation to change the physical appearance of that animal. An example would be black as opposed to red coat colour.

A “recessive” trait is one that is only physically observable when a calf inherits a mutated copy of the gene from both parents. An example of a recessive trait is red coat color. A red calf has inherited two red genes, one from each parent.

Two copies of the mutation are necessary to change the physical appearance of that animal. For this reason, an animal with only one copy of the recessive gene will typically not show any sign of the trait and is usually referred to as a “Carrier.”  An animal with two copies of the recessive mutation will show the trait and is designated “Affected.”  Only a cross between two Carrier parents or between Carrier and Affected parents can create another Affected animal.

Most animals are actually Carriers of a mutation somewhere in their DNA for one or many recessive traits. Because an animal must inherit two copies of a given recessive mutation to be Affected, and with only a few animals typically sharing the same mutation in the whole population, there is rarely a mating cross that has the potential to create Affected offspring under natural random selection.  Many abnormal recessive traits are never even discovered.

However, under the selection pressure of most current breeding strategies, and given the relatively small founding population of Speckle Park cattle, it is common to utilize a backcross and line breeding with a highly regarded sire or dam line. If the original sire or dam was a Carrier, there is a percentage of its generational offspring that will also be Carriers.  In this case, it creates a higher-than-average frequency of Carriers and potentially Affected cattle in the population.  Artificial insemination of a popular sire which is a carrier of a recessive gene is capable of spreading this gene throughout a population much faster than when bulls are only used in natural breeding conditions. The same is to be said dams used in embryo programs.  This has also happened in the Speckle Park breed.

What are the Three Recessive Genetic Conditions in Speckle Park?

Every species of animal, cattle included, have traits which are the result of recessive genes as well as traits which are the result of dominant genes.   Some traits of each type have a positive value and other traits a negative value.  These are the three recessive genetic conditions currently under scrutiny in Speckle Park.  Two (red and horned) render an animal ineligible for CSPA registration.  The third (double muscled) is considered by most commercial cattlemen to render an animal dysfunctional in the beef industry.

1.     Red Coat Color.   Red is the recessive to black coat colour.  The gene responsible for black coat colour is dominant to the gene responsible for red coat colour.  ED (sometimes printed Ed ) designates the dominant gene for black; the letter e designates the presence of the recessive gene responsible for red.  An EDED is black colour, does not carry any gene for red, and cannot produce a calf carrying the red gene.  On coat colour tests the EDED animal is referred to as homozygous for black.  In this discussion this animal is designated as “FREE” in the sense that it is free of the recessive red gene.

            Some black animals are black but carry the recessive gene for red (e). 

On test results these animals are designated EDe (Ede) heterozygous black or red carriers.  Red carriers will pass a red gene to half of their calves.  If the calves also get a red gene from their other parent they will be red.  In the following discussion these animals are designated “Carriers.”

Red animals have two genes for red coat colour.  On test results these will be designated ee and called homozygous red.  In this discussion of recessive traits these are designated as “Affected.”

Although it is true that all cattle are red once the hides are removed, there may be economic consequences to the red coat colour.  Although red is the only allowable colour in Herefords, and although many commercial cattlemen are okay with red, red is not acceptable to all.  In Speckle Park there are economic consequences associated with the red colour at three points.  1.  CSPA By-laws prohibit the registration of red Speckle Park of any pattern.  2.  The production of red calves through embryo transfer as a result of using two red carriers will incur significant financial expense to the breeder and may be extremely detrimental to customer satisfaction.  3.  Commercial cattlemen with black herds may not want to introduce red genetics into their herd.  Selling a red carrier can affect customer satisfaction.

2.     Horned.  Horns are recessive to polled.  Polled is the result of a dominant gene designated P.  Horned is the result of a recessive gene usually designated p.  A pure polled animal, that is one with two polled genes, has no horns because the animal has no genes for horns.  This animal will only produce polled calves.  When bred to a horn carrier or a horned animal, some of the calves will be horn carriers. On the test results such an animal is designated PP and homozygous polled.   In the following discussion the pure polled animal is designated “Free.”

Horned is an animal with horns.  This animal has no gene for polled and thus cannot produce polled calves unless bred to a polled animal.  On test results a horned animal is designated pp and homozygous horned.  In the following discussion this animal is designated “Affected.”

Some animals look polled but still carry a gene for horns.  Since the polled gene is dominant to the horned gene, the polled condition is what you see.  These animals do not show horns but can produce horned calves when the other parent is horned or a horn carrier.  In the genetic tests such an animal is designated Pp, heterozygous polled, or a horn carrier.  In the discussion below such animal is designated “Affected.”

Scurs are not horns.  Scurs and horns arise from different causative genes on different chromosomes.  That being said, there still is a connection between scurs and horns.  A horn gene has to be present for a scur to be present.  In short, every scurred animal is a horn carrier, that is, heterozygous polled (Pp).    However, not every heterozygous polled (Pp) animal is scurred.  In addition, pure polled animals can carry one or two scur genes and still not show scurs, just because they are pure polled and don’t carry a horn gene.

Speckle Park are a polled breed and therefor there is an economic cost to producing horns.  CSPA By-laws specifically prohibit the registration of any horned Speckle Park.  Horned carriers can be registered but since they can produce horned calves there is an economic cost but one just put off for a generation.  Furthermore, as the beef industry changes its management practices horned cattle and horned carriers are becoming increasing undesirable as herd sires in commercial herds.

3.     Double Muscling.  Double muscling is the recessive to normal muscling.  Myostatin is a regulatory protein that controls and limits muscle growth to normal ranges.  The production of the myostatin hormone is regulated by a dominant gene designated M.  This gene has mutated several times to produce various recessive genes which inhibit in various ways the production of the regulatory myostatin.  Animals lacking myostatin have significantly increased muscle growth. As a group of recessive genes they might have been designated as m, but since scientists have identified at least seven of these recessive genes and how each specifically functions to affect myostatin production, each recessive have each been given its own designation.  The myostatin recessive identified in Speckle Park is known as nt821 or sometimes NT821.  For a more detailed and illustrated description of double muscling consult “Double Muscling (Myostatin) and Speckle Park” in the Member Centre on the CSPA Website.  Click here.

Normal.  Myostatin normal.  The animal with two normal dominant genes for myostatin production is designated MM and does not produce animals with double muscling and the associated characteristic production traits.  Test results for the MM animal are reported as “0, no variants present,” that is to say, normal myostatin.  In the discussion below this animal is designated “Free.”  Many heavily muscled Speckle Park are MM, that is, normal.

Double Muscled.  The animal that has two recessive variants is designated mm and is genuinely and accurately called “double muscled.”  This is the animal with the most extreme expression of muscling such as Belgium Blue and Piedmontese.  The “doubled muscled” individuals are the ones most affected by the calving, management and movement issues associated with double muscling.  This animal has two mutant genes for double muscling.  All of this animal’s progeny will be double muscle carriers.  Test results for this mm animal are reported as “2, NT821” if the recessive mutation is NT821.   In other words the animal has two recessive genes and both identified as NT821.  This animal might also be called “homozygous for double muscling.”  In the discussion below this animal is considered “affected.”

Please be accuratewhen describing animals, especially Speckle Park.  In our carelessness animals which only carry one mutated gene for double muscling are often simply being called “double muscled” without any distinction between the homozygous double muscled (mm) and the heterozygous double muscled (Mm) animal which is only a carrier.  See the next paragraph.

The Carrier.  The “double muscle carrier” has one gene for regular mystatin production and one recessive which impairs myostatin production.  The double muscle carrier may be designated as Mm but test results are more specific and report the carrier as “1, NT821,” that is to say, one recessive variant present and the NT821 identifies which variant.  Sometimes this carrier may be referred to as heterozygous for double muscling.  The degree to which the variant gene causes the characteristics of double muscling to be seen can vary considerably so that on the one extreme the American Angus Association’s bulletin on double muscling states that carriers cannot be identified by mere visual assessment (phenotype).  Testing is necessary.  On the other hand in Speckle Park carriers can often, but not always, be identified by the presence of the typical characteristics of double muscling.  For a more detailed description of double muscling read “Double Muscling (Myostatin) and Speckle Park” in the Member Centre on the CSPA Website.  Click here

The economic impact (positive or negative) of double muscling is often related to the management style in a given herd and the demands of the market.  Although the carcass yield grade is higher because of less bone, smaller internal organs and the meat leaner because of much less fat, these characteristics are not always valued.  This may be desired in some markets.  However the lack of fat has a serious negative effect on marbling and thus negative affect on quality grades in the current grading system.  The other characteristics of double muscle carriers may render them dysfunctional in the ranch setting.

           

PART TWO.  Managing Recessive Conditions.

Terminology in the following discussion of managing recessives.

Free

 

•Means the animal has two copies of the normal gene

•Also referred to as Normal and Unaffected

Carrier

 

• Means the animal has one copy of the normal gene and one copy of the recessive gene

•Also referred to as Positive

Affected

 

•Means the animal has two copies of the mutated gen

The Genetic Distribution of the Status of Offspring.

Results for Each Type of Mating

 

Mating

Offspring Distribution

Free

Carrier

Affected

Free x Free

100 %

 

 

Free x Carrier

50 %

50 %

 

Carrier x Carrier

25 %

50 %

25 %

Free x Affected

 

100 %

 

Carrier x Affected

 

50 %

50%

Affected x Affected

 

 

100 %

Managing Recessive Genetic Conditions in Speckle Park Cattle

Knowing Your Cattle.  In order to manage recessive genetic conditions, it is of utmost important that breeders to have an accurate understanding of the status of their cattle with respect to the presence of the recessive genes. Without knowing the Free, Carrier, and/or Affected cattle in a breeder’s herd, it is impossible to make informed choices so as to eliminate or reduce the risk of propagating the genetic conditions to future generations of cattle.  Actively addressing these genetic conditions today will pay dividends in the near future to both the breeder and collectively for the Speckle Park breed.

There are two ways to identify the animals that are free, carriers or affected. 

1.     Testing for genetic conditions through a recognized laboratory is the quickest and surest way of identifying genetic status of your animals for these three recessives conditions.  Although more costly, this is the surest and quickest way. 

2.     If the breeder has accurate detailed private breeding records, there may be some information which can be useful for one or more recessive traits.  For example, both parents of that red calf are red carriers, both parents of any horned calf are horned carriers, every scurred animal is a horn carrier and at least one of the calf’s parents is a carrier.  However in the case of double muscling testing is the only sure method.  And yet that huge calf that died at birth was possibly affected and both parents carriers.  That Speckle Park bull that produced even one red calf is a red carrier.  And one horned calf means he’s a horn carrier.  Unfortunately private herd records are less useful to affirm and animal is free of a recessive.  However there are some exceptions.  A bull bred to at least 10 red horned cows and never sired a horned or a red calf is 98% sure to be free of the horn and red recessives.  

Strategic methodsfor managing recessive genetic conditions are breeder specific and depend on the type of cattle operation, i.e., registered, seed stock (bulls, semen, embryos) for domestic or export, beef production, commercial, etc. Below are some suggested strategies for breeders to consider. The strategy selected will also be dependent on the size of the herd and production goals.  It should be noted that this list is not all inclusive.

1.     Test all animals and remove Affected animals from the herd. Always use Free animals to mate with any Carrier animals remaining in the herd. A commitment must be made to test all offspring from Carrier animals that will remain in the breeding herd. The Carrier rate will be reduced over time in future generations.

2.     Test all animals and remove all Affected animals and Carrier sires. Use only Free sires in the breeding program going forward. A commitment must be made to test all offspring from Carrier dams that will remain in the breeding herd. This will reduce the Carrier rate the same as in Strategy 1 above.

3.     Test and remove Carrier and Affected animals from the herd. Only use Free animals in the breeding program going forward. No further testing will be required. This Strategy will ensure a totally Free herd immediately and going forward.  This strategy is the most extreme and also the most expensive.  And frankly this strategy may not be feasible depending on the investment made in the herd.

4.     Test all animals and use Carrier and/or Affected animals ONLY in a terminal breeding program.

5.     Test all animals and use Carrier and/or Affected animals as recipients in the embryo program. If a cleanup bull is used, it should be Free. Offspring DNA verified to the cleanup bull must be tested for any animals that will remain in the breeding herd.

These are just five examples of management strategies that can be used exclusively or in combination with each other.

As discussed above, proper management strategy has a major impact on reducing the frequency of Carrier and Affected animals in a breeder’s herd. This next table demonstrates the reduction in the Carrier rate in future generations, when consistently using Free sires on Carrier dams and their future generational offspring.

How many generations to eliminate carriers?

Breeding Free x Carrier

 

Generation

Offspring Distribution

Free

Carrier

Affected

1st

50.00 %

50.00 %

 

2nd

75.00 %

25.00 %

 

3rd

87.50 %

12.50 %

 

4th

93.75 %

6.25 %

 

5th

96.88 %

3.12 %

 

6th

98.44 %

1.56 %

 

7th

99.22 %

0.78 %

 

However, it is very important to note that if at any point a Carrier sire is reintroduced the distribution reverts almost to that of the 1st generation.  For example, if a Carrier sire were reintroduced to the fourth generation dams, the fifth generation offspring would be 48.44% Free vs. 96.88, 50% Carrier vs. 3.12%, and 1.56% Affected vs. 0%.

On the other hand, continued use of carrier animals, will not decrease the number of carriers at all and certainly never eliminate them.  This next table shows the effect of continued practice of breeding carriers to carriers in a herd.

How many generations to eliminate carriers?

Breeding Carrier Sire x Carrier Dam

 

Offspring Distribution

Generation

Free

Carrier

 Affected

1st

25 %

50 %

25 %

2nd

25 %

50 %

25 %

3rd

25 %

50 %

25 %

4th

25 %

50 %

25 %

5th

25 %

50 %

25 %

6th

25 %

50 %

25 %

7th

25 %

50 %

25 %

In contrast to the previous table, when a Carrier sire is mated to a Carrier dam, and Carrier sires are used to mate with the future generational offspring dams, the offspring distribution remains constant through all future generations.  If a cattle operations has as its purpose the production of registered seed stock, 25% affected animals (e.g. red or horned) can be financially significant since these affected animals are not eligible for CSPA registration.  However, if a cattle operation has as its sole purpose to produce feeders and meat, then the 25% affected (red or horns) does not entail financial penalty.  The financial penalty may be more significant if the affected are homozygous double muscled because the viability of these calves is significantly reduced without additional management. 

Insanity:  Doing the same thing over and over again

and expecting different results.       

                                                 -- Author Unknown

CSPA Testing Policy  The Directors of the Canadian Speckle Park Association encourage all breeders to learn the genetic makeup of their Speckle Park so that they can make appropriate breeding decisions.  The CSPA Directors have implemented a Genomic Genetic Conditions Testing program to help breeders assess their breeding population and make sound breeding decisions.  For the details of this program, the rebates and submission forms read “CSPA Genomics and Genetic Testing Program” in the Member Centre on the CSPA web site.  Click here.

The CSPA does not deny registration to carriers of the recessive genes under consideration in this paper.  The CSPA rules of eligibility do deny registration to actual horned and red cattle (affected).  Since the carriers only pass the recessive genes to half of their progeny, with the use of testing the free progeny can be identified and the carriers eliminated over time.  This strategy allows breeders to make the best use of the genetics they have developed in their lines. 

As part of the strategy to encourage breeders to use testing in order to learn the genetic status of the breeding animals in their herd, the CSPA members approved a by-law amendment which reads as follows:

Effective January 1, 2019 all walking herd sires and all A.I. donor sires collected after this effective date must have the original laboratory report of the DNA tests for double muscling (myostatin), coat colour and polled on file with the Association before any of their calves may be registered. These reports will held in confidence and will not be made public without the authorization of the breeder and/or owner of the animal in question.

For the purpose of assisting breeders and buyers the Association will maintain a publically accessible list to which breeders can voluntarily submit DNA test results for identified individual animals with respect their being tested clear of, carrier of or affected with one or more specific genetic conditions.

Some may wonder why what may be perceived as a soft line is being taken in regard to carriers.  Some breeders may wish to implement extreme measures and cancel the registrations of all carrier Speckle Park at one time.  The CSPA Directors rejected this severe and drastic approach for three reasons.   1.) The cancellation of the registrations of all carriers of these three recessives will bring extreme financial hardship on many cattle operations.  2.) The threat of the cancellation of carriers will result in breeders not testing their breeding population.  3.) The elimination of these animals at one time will severely decrease the breadth of the Speckle Park gene pool.

Genomic and Genetic Condition Testing.  The compiled results of the tests of 123 animals from 10 herds as completed by Delta Genomics as of August 4, 2017 is as follows:

n  29% of the animals tested were carriers of the myostatin mutation NT821.  That only one animal was homozygous (two copies) for the recessive gene may reflect the nature of the breeder’s selection of samples to submit or that homozygous double muscled animals rarely survive birth.

n  17% of the animals tested were red coat colour carriers.  This number is lower than might be expected in a general population because the current rules of eligibility have consistently prevented affected animals from entering the Speckle Park Herd Book and the gene pool.

n  11% of the animals tested were horn carriers.  One animal previously identified as scurred was determined by testing to be homozygous horned.  As with the previous category, this number may be lower because the current rules of eligibility have prevented affected (horned) animals from contributing to the gene pool.  Other factors may be at play.  This number may be a reflection of the fact that very few scurred animals are being submitted for testing.  Many breeders are and have been selecting against scurred animals and therefore not testing for genetic conditions.

If you have any questions, please contact the CSPA Office, and the Business Manager will find some answers for you.