Multiple-Breed Genetic Evaluation Part 4

Genetic and Gametic Trends
Part 4 of a Series

As a part of the Simmental and Simbrah National Cattle Evaluation, genetic trends are produced to describe the genetic change that has taken place over time. The genetic trends are the average EPDs for calves born in each year. For the current evaluations, genetic trends are calculated for purebred Simmental and purebred Simbrah. The Multiple-Breed Evaluation (MBE) will provide genetic trends for defined groups of animals such as purebred Simmental or purebred Simbrah. Also, the MBE system summarizes the genetic merit of genes coming from a breed group present in calves born in a given year. This yearly summary of genes coming from each breed group is called a gametic trend. This trend uses information from every animal born in a given year to measure the genes from the different breed of founder groups. Every animal with some fraction of Simmental breeding will contribute to the Simmental gametic trend. Likewise, every animal with some fraction of Angus breeding will contribute to the Angus gametic trends.

The genetic trends for purebred Simmental using the Fall 96 evaluation and the MBE Evaluation are shown in table 1. For both evaluations, the base is defined by setting the average EPD of purebred Simmentals born in 1986 to zero. The differences between the average EPDs from the F96 and the MBE analyses reflect differences between the two evaluations. The biggest difference between the F96 and MBE evaluations is the difference in the maternal milk genetic trends.

 

BWT

WWT

YWT

MMK

MWW

 

Fí96

MBE

Fí96

MBE

Fí96

MBE

Fí96

MBE

Fí96

MBE

1970

-0.5

-0.2

-7.1

-6.5

-11.2

-9.8

-0.4

2.8

-4.0

-0.5

1975

-0.5

-0.4

-6.5

-6.9

-10.7

-10.9

-0.8

1.7

-4.0

-1.8

1980

-0.5

-0.6

-4.8

-5.3

-7.5

-8.3

-0.1

0.9

-2.5

-1.7

1985

-0.1

-0.1

-0.8

-0.8

-1.3

-1.4

0.0

0.1

-0.4

-0.3

1990

0.4

0.5

3.9

4.0

6.6

6.7

-0.2

-0.8

1.7

1.2

1995

0.4

0.3

9.0

8.3

15.0

13.6

0.7

-0.8

5.2

3.3

With the MBE system, the EPDs for Simmentals and Simbrah are directly comparable. The genetic trends for purebred Simmental and purebred Simbrahs are shown for the five weight traits in table 2. Comparing the average EPDs of calves born in 1995, the differences in average transmitting ability between Simmental and Simbrah are -.7 for birth weight, +12.3 for weaning weight, +23.1 for yearling weight, +1.3 for maternal milk, and +7.4 for maternal weaning weight. The differences between Simmental and Simbrah come from the differences between Simmental and Brahman that are included in the evaluation. Regardless of the base, the differences between Simmental and Simbrah will remain the same for each trait. The genetic trends show the change in each breed from 1983 to 1995. Using weaning weight as an example, the change in average weaning weight EPD from 1983 to 1995 was +11.1 for Simmental and +10.4 for Simbrah. The genetic trends for Simbrah are roughly parallel to the Simmental trends except for birth weight where Simbrah has increased birth weight EPD about 1 lb. more compared to Simmental.

 

BWT

WWT

YWT

MMK

MWW

 

SM

SMBH

SM

SMBH

SM

SMBH

SM

SMBH

SM

SMBH

1983

-0.3

-0.6

-2.8

-14.4

-4.6

-26.2

0.3

-2.4

-1.1

-9.6

1985

-0.1

-0.2

-0.8

-12.3

-1.4

-22.1

0.1

-1.5

-0.3

-7.7

1987

0.1

0.1

0.8

-11.4

1.4

-20.9

-0.2

-1.8

0.2

-7.5

1989

0.3

0.5

2.9

-9.2

4.9

-17.4

-0.7

-1.9

0.8

-6.5

1991

0.5

0.8

5.4

-6.7

8.9

-13.9

-0.9

-2.1

1.8

-5.4

1993

0.5

1.0

6.8

-4.9

11.2

-11.0

-0.7

-2.5

2.7

-4.9

1995

0.3

1.0

8.3

-4.0

13.6

-9.5

-0.8

-2.1

3.3

-4.1

It would be difficulty to compute a genetic trend for breeds other than Simmental or Simbrah. The ASA data base does not have enough purebred animals from other breeds to compute meaningful trends for those breed groups. However, the ASA data contains many animals with some Angus genes, some Hereford genes, some Brahman genes etc. All animals with a fraction of genes from a breed group contribute to the gametic trend for that breed group. The gametic trend is the average merit of genes from a breed group represented in calves born in a particular year. The trend is expressed on an EPD scale. Every calf contributes to the gametic trend of a breed group if the calf possesses genes from that breed group. Gametic trends are computed for the breed groups included in the MBE analysis: Simmental, Angus, Hereford, Brahman, Charolais, Limousin, Gelbvieh, American, British, Continental, Dairy, and Mixed.

In tables 3 to 5, the average effect of Simmental, Angus, Hereford, and Brahman genes are shown for birth weight, yearling weight, and maternal milk. In addition to the four breeds, gametic trends were computed for the F1 Simmental-Angus cross and purebred Simbrah. Using the gametic trends of the twelve breed groups, trends can be computed for any possible combination of the twelve breed groups. For example, the gametic trend for Simmental-Angus was created by averaging the Simmental and Angus trends. The purebred Simbrah gametic trend was computed as a weighted average equal to 5/8ths of the Simmental trend plus 3/8ths of the Brahman trend.

Compared to the average Simmental genes expressed in calves born in 1995, the difference between Angus, Hereford, and Brahman genes and Simmental genes were 7.6 lb., 9.4 lb., and 0.1 lb. of birth weight, respectively. The average merit of F1 Simmental-Angus genes was intermediate to the Simmental and Angus gene values, -2.5 lb. From 1970 to 1995, the average Simmental genes for birth weight increased 0.5 lb. while the average Angus genes in the ASA data increased 3.5 lb. The average Brahman genes sampled to create Simbrah increased 2.4 lb. from 1970 to 1995.

 

SM

AN

HH

BR

SM-AN

SMBH

1970

0.8

-9.8

-6.4

-1.2

-4.5

0.0

1975

0.2

-9.4

-6.1

-1.1

-4.6

-0.3

1980

0.1

-8.5

-6.0

-1.2

-4.2

-0.4

1985

0.5

-7.5

-6.0

-0.7

-3.5

0.0

1990

1.0

-6.7

-7.2

0.3

-2.8

0.8

1995

1.3

-6.3

-8.1

1.2

-2.5

1.

 

Examining the yearling weight gametic trends, the selection for increased weight is evident regardless of the breed contributing genes. From 1970 to 1995, the increase was 33.3 lb. for Simmental, 23.7 lb. for Angus, 22.4 lb. for Hereford, and 11.5 lb. for Brahman. For F1 Simmental-Angus and Purebred Simbrah genes, the increase in yearling weight transmitting ability was 28.5 and 25.1 lb., respectively. On an EPD scale, the difference between Simmental genes and Angus genes for calves born in 1970 was 49.5 lb. The difference was 59.5 lb. in 1995 between Simmental and Angus.

 

SM

AN

HH

BR

SM-AN

SMBH

1970

-11.1

-60.6

-66.2

-65.3

-35.9

-31.4

1975

-5.8

-58.6

-64.9

-64.6

-32.2

-27.9

1980

-1.6

-54.2

-63.8

-64.8

-27.9

-25.3

1985

5.2

-50.4

-60.8

-62.8

-22.6

-20.3

1990

13.3

-44.4

-55.3

-58.2

-15.6

-13.5

1995

22.2

-36.9

-43.8

-53.8

-7.4

-6.3

For maternal milk, the average Simmental genes decreased 3.5 lb. from 1970 to 1995 while the average Angus genes in the ASA data decreased 1.1 lb. The gametic trends for Hereford and Brahman increased 9.4 lb. and 5.0 lb. from 1970 to 1995, respectively. For calves born in 1995, the average difference in the ASA data between Simmental and Angus genes was 12.6 lb. for maternal milk EPD. The average merit of F1 Simmental-Angus in 1995 was equal to the average Brahman genes in calves born the same year. The average merit of purebred Simbrah genes for maternal milk was 2.4 lb. less than Simmental and 3.9 lb. higher than F1 Simmental-Angus.

 

SM

AN

HH

BR

SM-AN

SMBH

1970

4.1

-10.6

-20.4

-10.4

-3.3

-1.4

1975

3.2

-10.3

-19.6

-9.3

-3.6

-1.5

1980

2.6

-10.5

-18.3

-8.1

-4

-1.4

1985

1.6

-9.8

-17.4

-6.5

-4.1

-1.4

1990

0.6

-11.3

-16.7

-5.2

-5.4

-1.6

1995

0.9

-11.7

-11

-5.4

-5.4

-1.5

Summary

With the MBE System, two types of trends can be produced, genetic and gametic. Genetic trends are produced for a defined group of animals such as purebred Simmentals or purebred Simbrahs. The trends represent the average EPD for calves born in each year. Gametic trends are the yearly average value of genes from a particular breed group in calves born each year. Every animal in the data contributes to the gametic trend depending upon the breeds represented in the animals pedigree. For example, a calf that is 25% Simmental, 50% Angus, and 25% Gelbvieh will contribute to the Simmental, Angus, and Gelbvieh gametic trends. The gametic trends can be used to produce trends for any particular cross of interest based on the information in the ASA data.

The genetic trends for purebred Simmental in the Fall 1996 evaluation and the MBE evaluation were very similar except for maternal milk in the 1970s and early 1980s. The difference between the trends was due to the differences in the records are handled by the two evaluation systems. The EPDs for Simmental and Simbrah animals are directly comparable using the MBE system.

The gametic trends describe breed differences based on all calves born each year. These gametic trends can be used to predict trends for crosses such as F1 Simmental-Angus or F1 Simmental-Brahman. The gametic trends can be used to set the base for any year and breed combination.

All EPDs are expressed relative to some zero point or base. For the purebred Simmental evaluation, the base is defined by making the average EPD of purebred Simmentals born in 1986 equal zero. The purebred Simbrah evaluation defines the base by making the average EPD of purebred Simbrahs born 1986 equal zero. The MBE will require some group to be set to zero. During a meeting at Cornell University, John Pollak said "The opportunity exists to set the base based on you want people to look at your EPDs and think about your cattle. We ask only that all traits be treated the same."