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By Dr. Ibne Ali, IMN PyrophosUpdated October 20269 min read
Decoding Sire Summary: A Practical Guide to Dairy Cattle Genetics

A Guide to Genetic Evaluations and Sire Selection in Dairy Cattle

1. Introduction and Purpose:

  • The workbook aims to provide a basic understanding of genetics and dairy cattle breeding, which is essential for using sire summaries effectively.
  • It emphasizes the importance of genetic evaluations in selecting superior parents and improving future generations.
  • The document notes that genetic evaluations have become increasingly complex since their introduction in 1935.
  • It highlights how an awareness of dairy cattle genetics can improve a herd's genetic progress.

2. Major Factors Influencing Genetic Change:

  • The primary goal of dairy producers is to maximize profitability by having a genetically superior herd.
  • Genetic change is permanent and accumulates over time.
  • Four major factors influence genetic change:
  • Accuracy of Selection: The ability to select animals that are genetically superior for a given trait. It depends on genetic evaluation techniques like the Animal Model.
  • Selection Intensity: The proportion of animals kept as parents and their superiority compared to the average population.
  • Genetic Variation: The relative differences among animals controlled by genetic factors, measured by the heritability of a trait.
  • Generation Interval: The average age of a parent when offspring are born.
  • The document provides a formula for calculating genetic change: Genetic Change = (Accuracy of Selection x Selection Intensity x Genetic Variation) / Generation Interval.
  • Rapid genetic change is achieved with high accuracy of selection, genetically superior parents, highly heritable traits, and shorter generation intervals.
Decoding Sire Summary: A Practical Guide to Dairy Cattle Genetics

3. Definitions of Genetic Terms:

  • Cell: The smallest structural unit of an organism, containing genetic material in the nucleus.
  • Chromosomes: Structures in the cell nucleus that contain genes, with dairy cattle having 30 pairs. Humans have 23 pairs.
  • DNA: Deoxyribonucleic acid, the chemical component of chromosomes, arranged in a double helix structure.
  • Genes: Hereditary units that determine an animal’s characteristics and are part of DNA.
  • Locus: The region on a chromosome where a particular gene is located.
  • Allele: One component of a gene pair at a given locus.
  • Meiosis: Cell division that creates sperm and eggs, each containing half the number of chromosomes as other cells. A random sample of one allele from each locus is found in the sperm and eggs.
  • Mendelian Segregation: The random process during meiosis determining which allele of each gene is in a sperm or egg.
  • Phenotype: The observable or measurable characteristics of an animal (e.g., milk record or classification score).
  • Genotype: The actual genes an animal possesses for a trait. In quantitative traits, genotype is expressed as the breeding value.
  • Dominant-Recessive: At each locus there are two alleles. In some cases, one allele is dominant over the other in determining the trait. An example is coat color in Holsteins, where black is dominant (B) and red is recessive (b).
  • Heterozygous: An animal with two different alleles at a locus (e.g., Bb).
  • Homozygous: An animal with two identical alleles at a locus (e.g., BB or bb).
  • Qualitative Traits: Traits controlled by one gene pair, with a direct relationship between genotype and phenotype, such as sex or hair color.
  • Quantitative Traits: Traits controlled by many genes, with each gene having a small effect, such as milk production and fat percentage. These traits are also significantly influenced by the environment.
  • Environment: The external conditions that influence an animal's production and quantitative traits. A majority of the difference in cow's production is attributed to the environment.
  • Environmental Variance: The difference in performance due to environmental effects. Genetic evaluations account for this variance.
  • Breeding Value: The total genetic ability of an animal for a given trait, with each parent contributing half.
  • Transmitting Ability: An estimate of the average genetic merit passed from parent to offspring (half of the breeding value).
  • Heritability: The proportion of variation in a trait due to genetic factors, ranging from 0.0 to 1.0. Higher heritability leads to faster genetic progress.
  • Generation Interval: The average age of a parent when offspring are born. A shorter generation interval increases the rate of genetic change.
  • Inbreeding: Mating closely related animals, which can increase homozygosity and undesirable recessive traits, and negatively affect health, vigor, and production.
  • Crossbreeding: Mating purebreds from different breeds to improve performance, health, and reproductive performance.
  • Correlated Response: Genetic changes in other traits when selecting for one trait.
  • Variation: Differences in genetic merit due to random sampling of alleles.
  • Undesirable Recessives: Defects that may cause poor health or death, usually controlled by one gene. If an animal is homozygous for the recessive allele, the condition will be expressed.
  • Progeny: An animal’s offspring.

4. Genetic Evaluations:

  • Genetic evaluations are updated by the USDA and breed associations to provide accurate information for dairy breeders.
  • The Animal Model is the current method for genetic evaluations. It accounts for environmental and genetic factors to minimize inaccurate and biased proofs.
  • Factors considered in genetic evaluations include:
  • Herd Management Effects: Comparing daughters of bulls with their herdmates to minimize differences due to herd management.
  • Genetic Competition of Herdmates: Accounting for the genetic merit of herdmates.
  • Genetic Merit of Mates: Considering the genetic merit of the other parent when evaluating an animal.
  • Environmental/Sire-by-Herd Interaction: Addressing management differences for daughters of different bulls.
  • Ancestor Information: Including ancestor information in calculations.
Decoding Sire Summary: A Practical Guide to Dairy Cattle Genetics
  • Predicted Transmitting Ability (PTA): An estimate of genetic superiority an animal will transmit to its offspring. PTAs are calculated for various traits, including milk, fat, protein, somatic cell score, productive life, net merit, and final type score.
  • Genetic Base: A reference point for genetic evaluations, with the average PTA for all cows born in a certain year set to zero. The base changes every five years.
  • Standard Transmitting Ability (STA): Standardized values for linear type traits used because each trait has a different average PTA, and the ranges vary within traits. The average STA is 0.
  • PTA Dollars (PTA$): An economic index combining relative values of milk and its components.
  • Percentile: Indicates how an animal ranks relative to others. Bulls are ranked on Net Merit, while USDA's Elite Cow list is based on the percentile ranking for MFP$.
  • Animal Model: Implemented in 1989, it incorporates information from the animal, its ancestors, and its progeny, using all records of female ancestors and descendants.
  • Linear Composite Indexes: Combine linear descriptive type information into single number values for Udder (UD), Feet and Legs (FL), Body Form (BD), and Dairy Capacity (D).
Decoding Sire Summary: A Practical Guide to Dairy Cattle Genetics

5. What are Sire Summaries:

  • Sire summaries are publications by breed organizations containing genetic information on production and type traits.
  • They include information on production traits (milk, fat, protein), type traits (final score, linear traits, composite indexes), and health/management traits (productive life, somatic cell score, calving ease, daughter pregnancy rate).
  • The USDA calculates genetic evaluations for production quarterly. Breed associations compute genetic values for type traits.
  • The first Holstein sire summary was published in 1967 and has evolved over time.
  • Multiple-trait Across Country Evaluations (MACE) are released by INTERBULL to compare sires from different countries.
  • Sire summaries assist dairy producers, A.I. organizations, and others with breeding, merchandising, and marketing decisions.
Decoding Sire Summary: A Practical Guide to Dairy Cattle Genetics

6. Parts of the Sire Summaries:

  • Holstein sire summaries are published three times a year and divided into sections.
  • Section 1 includes the Top 100 TPI bulls with high reliability and the Top 50 Sire Lists for various traits.
  • Section 1 contains production and type information on the top 400 TPI bulls with available semen and high genetic rankings. It also includes a linear profile and proof block for each sire.
  • Section 2 includes limited genetic information on Active, Limited, or Foreign bulls.
  • Section 3 includes the top 100 TPI Inactive Sires and Top 100 TPI Sires with high reliability, as well as Red and Red Carrier Sires ranked by TPI and the Top 100 TPI International Bulls.

7. How to Read Sire Information (Practical Step by Step Protocol):

The document provides a detailed guide on how to read sire information, which can be summarized as follows:

Decoding Sire Summary: A Practical Guide to Dairy Cattle Genetics
  • Block A: Identification and Pedigree Information:
  • Line 1: Bull's Registration Name and Total Performance Index (TPI).
  • Line 2: Nation Code, Registration Number, %RHA, Genetic Test Results, Final Score, Birth Date, and Recognitions.
  • Line 3: Sire’s Name and TPI Value.
  • Line 4: Sire’s Nation Code, Registration Number, %RHA, Genetic Test Results, Classification Score, Recognitions.
  • Line 5: Dam’s Name and CTPI Value.
  • Line 6: Dam’s Nation Code, Registration Number, %RHA, Genetic Test Results, Final Score, Classification Breakdowns, and Recognitions.
  • Block B: Production Summary:
  • Line 1: Milk: PTA, % Reliability, Sire’s PTA, Dam’s PTA, Daughter Averages, and Management Group Average.
  • Line 2: Fat: PTA, PTA %, Sire’s PTA, Dam’s PTA, Daughter Averages, and Management Group Average.
  • Line 3: Protein: PTA, PTA %, Sire’s PTA, Dam’s PTA, Daughter Averages, and Management Group Average.
  • Line 4: Evaluation Date, Number of Daughters and Herds, Percentage of Records in Progress (RIP), and Percentage of Daughters in U.S..
  • Block C: Additional Genetic Information:
  • Line 1: Productive Life: % Reliability, Sire’s PTA, Dam’s PTA.
  • Line 2: Somatic Cell Score (SCS): PTA, % Reliability, Sire’s PTA, Dam’s PTA, % Difficult Births in Heifers (Calving Ease), and Calving Ease % Reliability.
  • Line 3: Net Merit ($), Cheese Merit (CM$), and Fluid Merit (FM$).
  • Block D: Type Summary:
  • Line 1: Type: PTA, % Reliability, Sire’s PTA, Dam’s PTA, Daughter Averages for Final Score (SC), and Average Age Adjusted Score (AASC).
  • Line 2: Udder Composite (UDC): Linear Composite Index for Udder (UDC), Sire’s UDC, and Dam’s UDC.
  • Line 3: Feet & Legs Composite (FLC): Linear Composite Index for Feet & Legs (FLC), Sire’s FLC, Dam’s FLC, Body Size, and Dairy Capacity.
  • Line 4: Evaluation Date, Number of Daughters and Herds, and Effective Daughters per Herd (EFT D/H).
  • Block E: Ownership Information:
  • Line 1: Name and State of the Bull’s Breeder.
  • Line 2: Name and State of the Bull’s Owner or Lessee.
  • Line 3: Name of the Bull’s Controller.
  • Block F: NAAB Data Information:
  • Line 1: Semen Status.
  • Line 2: NAAB Number and Sampling Code, Sampler Controller Number.
  • Line 3: Short Name.
  • Block G: Trait Name Block: Displays the names of 23 traits for which STA values are graphed.
  • Block H: Standard Transmitting Ability (STA): Displays STAs for each of the 23 traits.
  • Block I: Biological Extremes: Highlights traits where a bull's STA is in the top 20% of the available bull population.
  • Block J: Trait Profiles: A graphic representation of the STA and Confidence Range for each trait.

8. Genetics in the Future:

  • The document discusses several techniques used to accelerate genetic improvements:
  • Embryo Transfer (ET): Increases selection intensity and reduces generation intervals by producing more offspring from elite dams.
  • Cloning: Creates multiple copies of an embryo.
  • Multiple Ovulation and Embryo Transfer (MOET): A process designed to increase genetic improvement by comparing progeny within a single herd.
  • Transgenic Animals: Involves injecting DNA into one cell embryos to introduce specific desirable genes from other species.
  • Genetic Markers: Identifies structural differences in DNA to link specific production traits with patterns.
  • Embryo Sexing: A process to determine the sex of an embryo before implantation.

Need help with feeding or a health problem in your cows or buffaloes? Message Dr. Ibne Ali on WhatsApp.

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