Basic Beef Cattle Genetics

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Basic Beef Cattle Genetics

• Scott P. Greiner, Ph.D.
• Extension Animal Scientist, Beef
• Virginia Tech

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Commercial Breeding Programs

• Merchandise pounds
• Goal
• Maximize output per unit of input
• Optimize performance within resources while
  maintaining low cost

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Genetic Improvement

• Crossbreeding
• Breed complimentarity
• Heterosis/Hybrid Vigor
• Within-breed Sire Selection
• EPDs

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Economically Important Traits

• Reproductive efficiency
• Calving rate
• Calf survival
• Weaning Wt.
• Post-weaning growth
• Cow longevity
• Cow lifetime production

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Crossbreeding Advantages

• Crossbred animals exhibit heterosis (hybrid
  vigor)
• Individual Heterosis
• Maternal Heterosis
• Crossbreeding allows for combining of strengths
  of different breeds

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Heterosis (Hybrid Vigor)

• Breed A Weaning Wt. 530 lb.
• Breed B Weaning Wt. 470 lb.
• A x B Crossbred Calf
• 500 lb. expected (average of A and B)
• 520 lb. actual
• 4 increase Heterosis

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Individual HeterosisAdvantage of the Crossbred
Calf
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Maternal HeterosisAdvantage of the Crossbred Cow

• Advantage of crossbred cow vs. straightbred
• Reproductive efficiency
• Calf weaning weight
• Increase pounds of calf weaned per cow exposed

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Maternal Heterosis
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Impact of Heterosis
Heritability Very Low Moderate High
Heterosis High High Very Low
Reproduction Growth Carcass Merit
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Breed DifferencesGrowth Performance
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Breed Influence on Carcass Merit

• British Biotypes
• 64 Choice and Prime
• 55 YG 1 and 2
• Continental Biotypes
• 45 Choice and Prime
• 81 YG 1 and 2

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Crossbreeding Program Goals

• Maintain high levels of heterosis
• Utilize breeds/genetics that fit-
• Environment/feed resources
• Management
• Marketing system
• Simple, manageable system

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Two-Breed Rotation
daughters
daughters
-Cows mated to opposite breed of sire -Requires
two breeding pastures
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Rotational Systems
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Rotational System Challenges

• Breeds utilized must be compatible in mature
  size, birth weight, and milk production
• Need similar adaptation to feed and production
  resources
• Several management groups
• Identification critical

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One Sire Breed- Change Every Few Years

• Modified rotational system
• Rotate breed of sire every 2-3 years
• Levels of heterosis maintained less than
  rotational system
• Increase pounds of calf weaned per cow exposed
  10-15

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Crossbreeding Challenges

• Number of cows
• Number of breeding pastures
• Labor/management
• Obtaining right mix by using purebred bulls
• Potential decreased uniformity in rotation
  (variation between calf crops)

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Making Crossbreeding Work

• Incorporate AI
• Purchase Replacements

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Using AI

• Decreases number of bulls needed
• Access to superior genetics of all breeds
• Example Breed superior cows AI for replacement
  heifer production, breed rest of cows to terminal
  sire
• Natural service sire used as terminal sire

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Purchase Replacements

• Crossbred female
• Maternal heterosis
• Mate to terminal sire
• Calving ease, growth, carcass
• System advantages-
• High heterosis
• Management simple
• Bull selection simplified

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Ideal Breeding SystemTerminal Crossbreeding

• Crossbred cow highly adapted to resources, with
  optimum reproductive potential, calving ease,
  milk, growth (minimum carcass merit parameters)
• Terminal sire bull selected primarily for
  post-weaning performance efficiency and targeted
  carcass merit

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Terminal Cross
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Terminal Sire Systems

• Utilize Rotational Cross for younger half of cow
  herd
• Generate replacements
• Older cows bred to terminal sire
• All offspring marketed (max. heterosis)
• Increase pounds of calf marketed per cow 20-25

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Bull Selection- Job 1
Most genetic progress is made through sire
selection.
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Bull Selection- Job 1
1. Selection of bulls within breed as important
as selection of breed
2. Genetic variation is large within any breed
for any given trait
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Expected Progeny Difference
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Expected Progeny Differences
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Milk EPDs
Daughters of Bull A should wean calves that are
10 lb. heavier than calves from daughters of Bull
B (due to superior milking ability)
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Birth Weight Weaning Weight Yearling Weight
Maternal Milk Maternal Weaning Weight
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Other EPDs

• Scrotal Cir.
• Calving Ease
• Gestation Length
• Stayability
• Mature Daughter Height Weight
• Docility

• Carcass
• Carcass Weight
• Fat Thickness
• Ribeye Area
• Retail Product
• Marbling

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What EPDs are Not

• Predict average differences between sires- not
  actual performance
• EPDs do not predict uniformity or variation in
  calf crop
• Not an absolute guarantee

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Expected Progeny Difference
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What EPDs are Not

• Not static
• Breed average EPD for any trait is not
  necessarily 0
• Not directly comparable across breeds

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Angus Genetic Trend
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Breed Average EPDs
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EPD Accuracy

• Measure of reliability
• Indicator of risk
• Increases as more information is used to
  calculate EPD

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Possible Change
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Accuracy
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Effective Use of EPDs

• Know Breed Average EPDs
• Understand Percentile Rankings
• Recognize Breed Differences

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Angus Percentile Rankings
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Breed Comparison
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Effective Use of EPDs

• Keep records of bulls progeny performance
• Track level of performance for given EPD value
• Prepare to make trade-offs!

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Bull Buying- Whats the Target?

• Heifer Bull?
• Keep Replacements?
• Sell Feeders?
• Retain Ownership?

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Specification Bull Buying-

• Terminal Sire
• Calving ease, Optimum growth, Carcass merit
• Rotational Sire
• Calving ease, Optimum Maternal Performance,
  Optimum Growth, Carcass Merit

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Important Bull Selection Data

• Individual EPDs
• Individual Performance
• BW, WW, YW, test ADG
• Son of High Accuracy, Proven Sire
• Pedigree- Dam performance
• REPUTABLE BREEDER

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Utilizing the Correct Bull

• No Breed Can Be Everything To Everybody!
• Utilize a particular breed for its intended
  purpose
• Recognize EPDs reflect differences within a
  particular breed
• Prepare to make trade-offs!

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Breed Average EPDsAcross Breed Basis
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Equivalent EPDsAcross Breed Basis
Milk EPD206 0
EPD RankWithin Breedtop 20bottom 10
bottom 10
AngusGelbviehSimmental
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Common Misconceptions

• Bigger is not always better
• Milk EPDs
• Negative is not necessarily bad
• Need to determine optimum

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EPDs Do Not Tell Us.

• Reproductive Efficiency
• Environmental Adaptability
• hardiness/adaptability
• structural soundness
• fleshing ability
• Health
• Disposition

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Crossbreeding Sire Selection Keys

• Frame size- best indicator of mature size
• Apply EPD selection on both a within-breed and
  across-breed basis
• Coat color and polledness are not limiting
  factors

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Cow/Calf Profitis determined by

• 1. Reproductive Efficiency
• 2. Early Growth
• 3. Maternal Ability
• 4. End Product Merit

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Genetic Progress in Multiple Traits

• Effective use of EPDs
• Application of well-designed crossbreeding system

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