Heterosis – The Forgotten Tool? Dr. Tom Field Colorado State University Dr. Andy Herring Texas A&M University Cattlemen’s College 2005 NCBA Meeting, San Antonio

General Comments The seedstock cattle industry exists as a business only because of the demands of the commercial cattle industry. Without purebred animals, F 1 crossbred animals cannot be produced.

Basics of Quantitative Genetics Performance = Genetics + Environment Genetic aspects are: 1. Additive (breeding value – gene content) 2. Non-additive (hybrid vigor – gene combinations) Alleles at a gene locus can act additively (or not). Genotypes across gene loci can act additively (or not).

Breeding Systems It is important to know breed characteristics to fully take advantage of breeding systemsIt is important to know breed characteristics to fully take advantage of breeding systems It is important to know characteristics of different types of breeding systemsIt is important to know characteristics of different types of breeding systems

Properly designed beef cattle crossbreeding programs have the potential of substantially improving production efficiency over commercial straightbreeding programs.

The improved efficiency from crossbreeding can result from: 1.Heterosis (hybrid vigor) 2.Blending, in the offspring, of characteristics from different breeds and/or, 3.Characteristics of the dams and sires as these characteristics, themselves, affect the efficiency of the system.

Heterosis Hybrid vigor (also called heterosis) is the higher performance of crossbred animals as compared to purebred animals. For a particular pair of breeds, the hybrid vigor for a particular character is the average amount that the average of the F 1 exceeds the average of the two pure breeds.

Heterosis Example: Weaning weight information Brahman average = 500 lb Hereford average = 460 lb B x H average = 516 lb H x B average = 540 lb HV =(( )/2) - (( )/2) = = 48 lb = 48 lb = 48/480 = 10% = 48/480 = 10%

Heterosis - most important for reproduction and survival traits -tends to be higher between breeds that are more genetically different from each other (2 to 3 times higher in Bos indicus/Bos taurus crosses than in Bos taurus/Bos taurus crosses) -highest in F 1, and tends to be proportional to degree of heterozygosity -especially important for female productivity (reproduction and maternal ability)

Crossbred Cows Because of heterosis for female productivity (fertility, calf weaning weight, longevity), much of the advantage from crossbreeding systems comes from the use of crossbred cow.

Maternally Influence Characters Performance for a maternally influenced character (such as weaning weight) is a function of 1. breed composition of the calf 2. heterosis in the calf (direct) 3. breed composition of the dam 4. heterosis in the dam (maternal)

How to Estimate Heterosis There are two major considerations here: 1.The actual amount of increased performance in units of the trait in F 1 animals. 2.The expected fraction (or percentage) of the F 1 advantage in other types of crosses.

How to Estimate Heterosis F 1 animals will exhibit 100% heterosis between the two breeds involved, but this is 100% of some actual advantage in performance. For example: In some F 1 crosses, this may be 100% of a 25 lb advantage, and in other F 1 crosses this may be 100% of a 40 lb advantage.

How to Estimate Percent Heterosis Heterosis percent (fraction) is based on the fraction of gene loci in animals that are expected to have two alleles from two different breeds. Angus bulls x Hereford cows => F 1 calves These calves are ½ Angus, ½ Hereford, but 100% of their gene loci are heterozygous.

How to Estimate Percent Heterosis If we take F 1 bulls and F 1 heifers and mate them: F 1 bulls (½ A ½ H) x F 1 heifers (½ A ½ H) => F 2 calves (½ A ½ H) The F 2 calves are expected to have ½ heterosis themselves (50% direct), but also benefit from heterosis in cows (100% maternal).

How to Estimate Percent Heterosis If you know the fractions of the breeds in the parents, you can estimate the fraction of heterosis in progeny (based on chance of inheritance). ½ A ½ H bulls x ½ A ½ Gelbvieh cows => ½ A ¼ H ¼ G calves Heterosis in calves can come from A-G, H-G, H-A combinations, each has ¼ chance of occurrence. We would say these calves have 75% heterosis.

Heterosis Heterosis increases production per cow 20 to 25% in Bos taurus x Bos taurus crosses and at least 50% in Bos indicus x Bos taurus crosses in subtropical regions.Heterosis increases production per cow 20 to 25% in Bos taurus x Bos taurus crosses and at least 50% in Bos indicus x Bos taurus crosses in subtropical regions. More than half of this effect is dependent on use of crossbred cows.More than half of this effect is dependent on use of crossbred cows.

Cumulative Effects Of Heterosis For Weight Of Calf Weaned Per Cow Exposed To Breeding Straightbred cows straightbred calves Straightbred cows X-bred calves X -bred cows X-bred calves Percent

Heterosis Utilization is Critical for Commercial Producers Consider pounds of calf weaned per cow exposed to breeding Cow-calf System Productivity* lb calf 1.Straightbred cows producing straightbred calves Straightbred cows producing crossbred calves Crossbred cows producing crossbred calves crossbred calves *Based on data from USDA MARC involving Bos taurus crosses and purebreds.

Heterosis Depends on Crossbreeding System and Breeds Type of systemExampleDirectMaternal Terminal F1 crossCharolais x Hereford100 0 Terminal F1 crossBrahman x Hereford200 0 Two breed rotationAngus, Hereford Two breed rotationAngus, Brahman Three breed terminal Charolais x F1 Angus-Hereford Three breed terminal Charolais x F1 Brahman-Hereford Three breed rotationAngus, Simmental, Gelbvieh Three breed rotationAngus, Brahman, Charolais143*143* Two breed composite50% Hereford, 50% Simmental % Angus, 50% Brahman /8 Charolais, 3/8 Red Angus /8 Shorthorn, 3/8 Brahman Four Breed Composite25% each A, H, S, C % A, Br, C, G % A, Br, L, Nellore *Some crosses in the system will exhibit more heterosis than others.

Average birth weights at the McGregor Station _______________________________________________________ Birth Weight (lb) Birth Weight (lb) Sire breedDam breed bullsheifers average _______________________________________________________ Hereford Hereford Brahman Brahman Hereford Brahman Brahman Hereford ______________________________________________________

Crossbreeding Systems A real challenge in beef cattle breeding is to develop effective, sustainable crossbreeding systems.

1. It should be possible for all the breeding stock that are needed for the system to be produced in the same region where the system will be operated. 2. The system should be fairly simple to operate. 3. All cattle used in and produced by the system should be adapted to the local environment. 4. There should be no major incompatibilities between the cattle that are mated. 5. All animals that are produced in the system must be acceptable to local market conditions. In order for a crossbreeding system to be sustainable in a region, it should have the following characteristics:

Example of Three Breed Composite Composite that is ½ Angus, ¼ Charolais, and ¼ Hereford 1/2A 1/4C 1/4H bulls x 1/2A 1/4C 1/4H cows => 1/2A 1/4C 1/4H calves Breed combinations in calves can be: A-C, A-H, or C-H.

Breed Combinations Breed Combinations in Calves ¼ A-A 1/8 A-C 1/8 A-H 1/8 C-A 1/16 C-C 1/16 C-H 1/8 H-A 1/16 H-C 1/16 H-H Cows ½ A ¼ C 1/4H ½ A ¼ C 1/4H Bulls ½ A ½ A ¼ C ¼ C ¼ H ¼ H Heterosis in calves = 1/8 +1/8 + 1/8 + 1/8 + 1/16 + 1/16 = 5/8 or 62.5% = 5/8 or 62.5%

Results From Research Projects

LONGEVITY AND LIFETIME PRODUCTION OF STRAIGHTBRED HEREFORD (H), ANGUS (A), HEREFORD X ANGUS (HA) AND ANGUS X HEREFORD (AH) COWS Breed group Trait H A HA AH Heterosis Longevity, yrs * Lifetime production No. calves * Wt of calves weaned, lb * *P <.05

TAMU Diallele Project Purebred and F 1 cows of Angus, Hereford, Brahman, Holstein and Jersey were evaluated over a 14 year period.Purebred and F 1 cows of Angus, Hereford, Brahman, Holstein and Jersey were evaluated over a 14 year period. Only production reason for culling was if cow failed to give birth to live calf every 24 months, or if cow appeared unable to raise another calf.Only production reason for culling was if cow failed to give birth to live calf every 24 months, or if cow appeared unable to raise another calf.

Breed type Percent remaining Productive life (yr) Angus710.3 Brahman179.7 Hereford59.8 Holstein07.3 Jersey06.2 Angus-Brahman Angus-Hereford Angus-Holstein Angus-Jersey89.9 Brahman-Hereford Brahman-Holstein Brahman-Jersey Hereford-Holstein Hereford-Jersey Holstein-Jersey08.8

Research Project in Nebraska Angus, Hereford and Shorthorn evaluated as purebred and as F 1 crossbred cows for cow productivity and longevity. Cows born and were kept until they were 12 to 15 years old.

Survival percentage to 12 yr and longevity (kept to yr old) Breed type Survival (%) Longevity (yr) Hereford Angus Shorthorn Hereford-Angus Hereford-Shorthorn Angus-Shorthorn

Mouth scores based on teeth length in aged cows Breed type Mouth score Hereford11.0 Angus11.8 Shorthorn10.3 Hereford-Angus15.1 Hereford-Shorthorn16.5 Angus-Shorthorn13.8 Higher number indicates more tooth remaining.

Reasons for Nebraska cows culled

TAMU Riesel Project Production of F 1 calves in by mating Angus, Gray Brahman, Gir, Indu- Brazil, Nellore and Red Brahman sires to Hereford cows.Production of F 1 calves in by mating Angus, Gray Brahman, Gir, Indu- Brazil, Nellore and Red Brahman sires to Hereford cows. All cows were kept to measure productivity and longevity.All cows were kept to measure productivity and longevity. Udder, teat and teeth soundness evaluatedUdder, teat and teeth soundness evaluated

Comparison of F 1 Cows at McGregor, TX through 14 years of age % CC lb calf per % still % CC lb calf per % still Type of cow BWT WWT weaned cow exposed in herd Angus-H % Gray Brahman-H % Gir-H % Indu-Brazil-H % Nellore-H % Red Brahman-H %

Comparison of F 1 Cows at McGregor, TX through 14 years of age Teats that were too large, and/or udders that were too pendulous caused increases in calf illness because it was difficult for calves to nurse on their own initially. Size of udder did not appear related to milk production within a breed. Nellore crossbred cows had smallest teats and tighest udders, and best overall production and longevity. All of Bos indicus-Hereford F 1 cows had better mouths later in life than Angus-Hereford F 1 cows.

Heterosis Retention Project at McGregor, Texas Initiated in mid 1990s to measure heterosis retention in Bos indicus-Bos taurus crosses.Initiated in mid 1990s to measure heterosis retention in Bos indicus-Bos taurus crosses. Purebred Angus, Hereford, Brahman and Nellore.Purebred Angus, Hereford, Brahman and Nellore. Cow reproduction and productivity major focus of project.Cow reproduction and productivity major focus of project.

Heterosis Retention Project - McGregor, TX Heterosis estimates for individual traits. %CCB%CCWWWT lb calf/cow B/A F lb (6.3%) 74 lb (23%) B/H F lb (20.7%) 146 lb (53%) B/A F lb (0.2%) -30 lb (-9%) B/H F lb (9.9%) 103 lb (37%)

Heterosis May Vary Across Environments There have been several research projects in cattle where there seems to be more heterosis expressed in more challenging environments.

Matching Genetic Potential to the Climatic Environment (Olson et al., 1991)

Note that important differences in environments can be across the fence from each other.

Summary Because of heterosis for female productivity (fertility, calf weaning weight, longevity), much of the advantage from crossbreeding systems comes from the use of crossbred cow.

Bad Breeding Decisions are Costly