Understanding Genetics For Use In Goat Production Dr. Dennis Onks Director Middle TN Research Center University of Tennessee
PHENOTYPE AN ANIMAL’S VISUAL EXPRESSION OR PERFORMANCE IN ANY TRAIT The Phenotype is the outcome of Genetic Transfer as developed in a production Environment
PHENOTYPE Defined as the sum of the genetic and environmental variation The Genetic variation accounts for 25% of The Phenotype while the Environment Accounts for 75%!
Sound Breeding Program Maximum Genetic Improvement occurs In a Herd Environment that allows the Improved Genetics to be Expressed
Sources of Environmental Variation • Weather • Land Topography • Structural Resources • Forages and Feeding • Health and Sanitation
How Traits are Inherited Genetic Variation is the study of • All body cells contain “Blueprints” with instructions as to how an animal will look or act etc. • DNA or Deoxyribonucleic Acid contains the genes of traits in the double helix ribbons located in every cell
GENE The combination of genes are attached to chromosomes which guide the animal to express A trait or response http://library.thinkquest.org
Species differ in chromosomes Humans 23 pairs of chromosomes Cattle 30 pairs of chromosomes Sheep 27 pairs of chromosomes Swine 19 pairs of chromosomes Chicken 39 pairs of chromosomes Goat 30 pairs of chromosomes Horse 16 pairs of chromosomes
How Traits are Inherited The science of ½’s since each living animal receives a Sample ½ of its genetics from its father and a sample ½ of its genetics from its mother. The process of halving is done by Meiosis
Gene Dominance One Gene overshadows The expression of its other pair (allele) We’re heterozygous (different) WW and Ww = White
Recessive Genes • The gene that is overshadowed by a dominant gene. Recessive genes can only be expressed when they both are present We’re Homozygous (the same) RED COAT COLOR = ww
QUALITATIVE TRAITS TRAITS THAT ARE AFFECTED BY A SINGLE OR A FEW PAIR OF GENES COAT COLOR TEETH HORNS
QUANTITATIVE TRAITS TRAITS AFFECTED BY NUMEROUS PAIRS OF GENES The thousands of genes present make countless combinations possible in an animal. Since genes are too small to identify individually, they express their presence by such outward effects as differences in growth, carcass or reproduction traits
Quantitative Traits (cont’d) Growth traits Birth weight Weaning weight Yearling weight Growth rate (ADG) Frame size Carcass traits Rib eye area Fat thickness Marbling Reproduction traits fertility/adaptability
Which buck has the best genetics for growth? Is the buck on the left bigger because he had better genetics for growth or because he was provided a better environment?
IMPROVEMENT OF ANY TRAIT DEPENDS: MEASURING DIFFERENCES IN A TRAIT ACCURATELY IDENTIFYING SUPERIOR INDIVIDUALS IN THE TRAIT USING SUPERIOR INDIVIDUALS AS PARENTS HOW HERITABLE THE TRAIT IS (heritability)
What is Selection? • Choosing animals to be parents for the next generation to produce certain characteristics • Low Birth weight • Heavier Weaning Weight • Gaining Fast • Horned or Polled • Temperament • Better Eating Quality
Heritability(h2) Percentage of the differences (measured or observed) in a trait between animals that are transmitted to the offspring. Reproduction fertility,etc. Low Production growth Moderate Product carcass High (Heritability is a measure of how a trait will respond to selection)
Table 1. Heritability Estimates for Goat Traits Low Heritable Traits • Birth Interval 5-10% • Number Born 15% • Rear Legs 15% • Udder Support 20% • Reproduction 15% By Dr. An Peischel @ 2001 ·Low Heritability (10-20%) ·Moderate Heritability (25-45%) ·High Heritability (50-70%)
Table 1. Heritability Estimates for Goat Traits Moderately Heritable Traits • Birth Weight 30-40% • Weaning Weight 20-30% • Yearling Weight 40% • Feed Conversion 40% • Quality Grade 40% • Ribeye Area 40-45% • Muscling 40-45% By Dr. An Peischel @ 2001 ·Low Heritability (10-20%) ·Moderate Heritability (25-45%) ·High Heritability (50-70%)
Table 1. Heritability Estimates for Goat Traits Highly Heritable Traits • Mature Weight 65% • Milk Fat 55% • Stature, Frame 45-50% • Carcass Weight 45-50% • Scrotal Circumference 50% By Dr. An Peischel @ 2001 ·Low Heritability (10-20%) ·Moderate Heritability (25-45%) ·High Heritability (50-70%)
Selection for traits is Impactedby the Correlation(r2)Between Traits • Genetic Correlation measures the genetic association between traits • Phenotypic Correlation measures the local or environmental association between traits • Correlation ranges in value of +1.0 to –1.0 (indicates the direction of association)
Phenotypic Correlations Body WT Length Heart Girth Backfat Loin Area Kidding Difficulty Length Heart Girth Backfat Loin Area Scrotal Circumference
Use of Heritability andCorrelations • Selection for Weight makes moderate progress (h2=40-65%) • Positive Correlation (r2=+.50) between birth, weaning and carcass traits means Selection will result in increases in all three traits.
Use of Heritability andCorrelations • Selection for Weight makes moderate progress (h2=40-65%) • Negative Correlation (r2=-.50) between Weight and Kidding Difficulty means Selection will result with increased Kidding Difficulty and birth, weaning and carcass weight.
Selection for the Industry • Consumer • Packer • Feeder • Commercial producer • Purebred Breeder • Each section may have differing trait criteria
CONSUMER • Price/ Value • Consistency • Holidays • Taste/ Flavor • Safety/ Health
PACKER • Dressing Percent • Quality Grade • Yield Grade
FEEDER • Health • Gain • Feed Efficiency
Commercial or Purebred Producer • Reproduction • Maintenance Cost • Growth • Weaning • Yearling
Heritability (Heritability is a measure of how a trait will respond to selection) Reproduction Low Production Moderate Product High “or how well the offspring resemble their parents phenotype”
MEASURABLE TRAIT (Phenotype) • GENETIC EFFECTS • ½ GENETICS FROM BUCK • ½ GENETICS FROM DOE • ENVIRONMENTAL EFFECTS • WEATHER • NUTRITION • HEALTH • Etc.
Measures of Phenotype P = G + E Birth weights Weaning weights Yearling weights Carcass Traits Reproductive traits Adaptability
Measures of Phenotype P = G + E Requires: 1. Identification of animals 2. Equipment to record trait measure 3. Record Keeping System 4. Computer with Spreadsheet is economical and recommended
Genetic Evaluations Phenotypes and Pedigrees Objective: convert data into genetic information for the purpose of selection Separate genetic portion of phenotype from environment.
90 DAYS OLD ON FARM “A” BUCK 2 YR DOE 105 DAYS OLD ON FARM “A” BUCK 4 YR DOE 41 lbs 38 lbs WHAT ARE THE KNOWN ENVIRONMENTAL EFFECTS?
Known Environmental Effects 650 680 • AGE • 15 DAYS+ 15 DAYS • AGE OF DOE • 2 YR OLD 4 YEAROLD • FARM • SAME SAME
Adjusted 90 day wt.formula (Actual Wt - Birth wt) X 90 + doe age adj. + birth wt Age in days Breed associations are calculating adjustments as they accumulate data from the breeders
Adjusted 90 day wt. (42 – 7) (41 –8) X 90 + 0 + 7 X 90 + 5 + 8 105 days 90 days = 36.999 Lbs. = 45.999 Lbs.
Contemporary Group Ratios adj. 90 day wt adj. 90 day wt 39 37 Buck A Buck B Herd Avg. = 36 Herd Avg.= 36 Ratio = 39/36 Ratio = 37/36 108 102.8 Useful for within herd selections but not between herds
We must expect differences between animals across different environments
Future Genetic Evaluations Source of data Ancestors Collateral relatives Descendents Own performance Correlated traits
(EPD)-Expected ProgenyDifference • A prediction of the genetics a goat will pass on to his kids, when compared to other goats within the breed • Takes into account the actual measurements, all ancestral measurements and environment • Not a perfect science, so use as a risk management tool
College Football BCS Purpose is to identify best college football teams Source of Data : AP ranking USA Ranking Record Strength of schedule etc. Ranking changes as more games are played
National Goat Evaluation Breed Specific Breed summaries report EPDs. Expected Progeny Difference And Breeding Values The American Boer Goat Association, American Dairy Goat Association, National DHI Program
Interpreting EPDs Provide a prediction of future progeny performance of one individual compared to future progeny of another individual within a breed for a specific trait. Allow one to compare or rank the genetic superiority of individual animals within a breed for a specific Trait. EPDs are reported in the actual unit that the trait is Measured (Lbs. for growth traits). They can be positive or negative numbers
Effective EPDs: Examples • Scrotal Circumference (SC) High SC bucks sire does with earlier Puberty • Birth Weight (BW) Low BW bucks have more live kids • Average Daily Gain (ADG) Allows choice for replacements or sale of weanlings • Carcass Merit (CM) Allows choice for direct or wholesale Marketing
Avg. Array of genetic value of an individual (EPD), adjusted trait performance
Difference in Array for two Bucks Full Brothers have a sample 1/2 genetics of buck & of the doe but Not necessarily the exact same genetics