Beef Cattle Selection and Crossbreeding Chapter Two Two

Beef Cattle Selection and Crossbreeding Chapter Two

Two Major Changes in Cattle Breeding • Introduction of “Exotic” Breeds • Shift Toward Crossbred Cows – Estimated 65 breeds in US – Must have “Niche” to survive

Beef Cattle Selection • Purebred Seedstock • Will Always be in demand • Development of Crossbreeds

Selection of Traits • Selecting for too many traits--> – little improvement in any trait • Selecting for only a single trait--> – deterioration of other traits. • Balance is essential

Factors Affecting Genetic Improvement

A. Heritability Differences between animals due to genetics

Heritability Factors • Traits have varying heritability • More Environmental Influence-> – Lower heritability • Heritability can be compared--> – if the environment is the same • Heritability Estimates Pg. 16

B. Selection Pressure The amount of difference between herd average and selected replacements

Selection Pressure • The greater the difference between the selected animal and the herd average, the greater improvement can be expected. • Selection pressure = A general term

Selection Differential • Specific Numbers • Average difference in phenotype between selected animals and herd average • Example, Page 17

C. Genetic Correlations The effect of one trait upon another

Positive Correlations • Inc. WW = Inc YW • Inc. Milk = Inc. WW • Inc. Feed Eff. = Inc. ADG • Inc. BW = Inc. WW = Inc. YW

Negative Correlations • Inc. BW = Inc. Dystocia • Inc. ADG = Inc. BW • Inc. ADG = Dec QG

D. Generation Interval Rate of turnover within the herd

Generation Interval • For herd improvement--> – Higher producing replacements – Must replace lower producing individuals • A replacement heifer must exceed the production of her mother for progress to be made.

Types of Individual Records

1. Pedigree • Family History • Record of Sire and Dam • Grandsires and Grandam • Implies similar production • Only information available on young or newborns

2. Performance Data • An individual’s own numbers • Not related to pedigree • Not related to offspring • Implies a genetic trait

3. Progeny Data • Performance of offspring • By far, the most important • Only available on older seedstock

4. EPD Data • A projection of offspring performance • ACC increases with more data • ACC increases with increased progeny data • Older bulls are more predictable

Determining EPD’s • Calculated by Breed Associations • Pedigree (young animals) • Performance • Progeny and Grandprogeny • Emphasis changes with age

EPD Factors • Age of Dam • Heritability of trait • Number of progeny • Available pedigree

More EPD factors • Contemporary Group Information • Mates of Sires • Sire Production Records • Related traits (management style)

EPD Definition • An estimate of how offspring can be expected to perform • when compared to others within the same breed • when bred to mates of equal value

Contemporary Group Information • Same Sex • Born within 90 days • Similar Management – creep fed, implant, castration • Same % breed • Weighed same day

Two Kinds of EPD’s • Direct influence on calf • Indirect EPD’s • Influences future production of daughters or sons

Direct EPD’s Examples

1. Birth Weight • Influences dystocia • Exp. in lbs. , compared to breed • +3 = calves from this sire will have XX% chance of producing calves that are 3 lbs heavier than breed average. • XX% = Accuracy

2. Weaning Weight • Indicator of Pre-weaning growth • Expressed in lbs. • Heavily influenced by milking production

3. Yearling Weight • Includes WW + Post-weaning Rate of Gain • Mostly used for Bull evaluation • Less important for commercial herds

4. Scrotal Circumference • Related to age at puberty and fertility • Measured in centimeters

5. Gestation Length • Measured in Days • Short GL = – Inc in Post Partum Interval – Dec BW – Inc. in age at Weaning

6. Carcass EPD’s • Marbling = %fat in REA • Carcass Wt • Rib-eye Area • Fat Thickness • % Retail Cuts

Indirect EPD’s Maternal traits that relate to Daughters future production.

1. Milk EPD’s • WW of calves of daughters sired by this bull (Grandprogeny) • Expressed in lbs. of WW • Should match feed and management resources • Largest not always best

2. Total Maternal EPD • Combines weaning and milk EPD’s • Expressed in lbs of WW due to both milk and growth • Milk EPD + 1/2 of WW EPD = Maternal

Other EPD Terms

Accuracy • Reliability Due to information available • Numeric Value = 0 to 1 – Increases as information increases – Low accuracy = Less reliable

P Accuracy • Based on Pedigree only • 1/2 of Sire EPD + 1/2 of Dam EPD • Used until Production Info is available

P+ Accuracy • Pedigree + Progeny Information

Comparing EPD’s • Do not compare across breeds • Different methods of determination

Crossbreeding Beef Cattle

Crossbreeding Definition • Mating animals of different breeds

Heterosis • Hybrid Vigor • The difference between- • A. The trait of the offspring • B. The average of his parents

Importance of Heterosis 3 major points

Importance of Heterosis #1 • Undesirable recessive traits are often covered over by more desirable dominant traits

Importance of Heterosis #2 • High heterosis strengthens desirable production traits

Importance of Heterosis #3 • The more diverse the breeds, the greater the heterosis will be.

Breed Complimentarity • No Breed is perfect • All have defects • Combining strengths creates more desirable offspring.

Terminal Cross • Produces calves for sale as feeders • No Breeding Stock Saved.

F 1 Generation • First Generation offspring of a Cross

Choosing a Breeding System • For Commercial Herds

Straight Breeding Options within a Single Breed

Inbreeding • • Bulls and Cows from same bloodline Not for commercial producers Minimim heterosis More Expression of undesirable traits • Strengthens Traits-Good and Bad

Outcrossing • • Different bloodlines--same breed Some heterosis Most common Maximizes performance within breed • Simple

Straight Breeding Advantages • Breed Identity-Important to some • Maximizes adaptability • Simple

Cross-Breeding Crossing Two or more Breeds

Advantages • Heterosis • Influences traits exhibited at early age most – BW-->WW • Great influence on low Heritability traits

Two Breed Cross • Simple • Easy to change breeds • Terminal cross

3 Breed Terminal Cross • Popular cross breeding method • F 1 cross female X Straight bred bull • Utilizes high heterosis females

More 3 Breed Cross Stuff • High Availability of Bulls • Usually terminal • High heterosis

3 Breed Rotational Cross • Maximum Heterosis • Stacks pedigrees • 6 or 12 year cycle • Requires records

6 Year Cycle • Yr 1 & 2 • Yr 3 & 4 • Yr 5 & 6 Hereford Charolais Angus

12 Year Cycle • Yr 1 & 2 • Yr 3 & 4 • Yr 5 & 6 • Yr 7 & 8 • Yr 9 & 10 • Yr 11 & 12 Hereford A Hereford B Charolais A Charolais B Angus A Angus B

Two Breed Criss-Cross • F 1 daughter bred to opposite breed of her sire • simple • Stacks pedigrees • Produce replacement females

Purebred Herds 2 General Methods

Purebred Inbreeding • Cows and Bulls from same bloodline • Enhances Traits-Good or Bad • Minimizes genetic variation between blood lines

Purebred Outcrossing • Uses 2 blood lines • Best for most producers