Livestock Breeding Systems Overview

Selection and Breeding Systems

• Animal breeding aims to improve livestock genetic makeup, enhancing productivity, disease resistance, and overall quality.
• This process heavily relies on selection and breeding systems.

Animal Breeding

• The goal is to improve the genetic makeup of livestock populations.
• This process is vital for enhancing various traits, including productivity, disease resistance, and overall quality.

Selection

• Selection is the act of choosing individuals to become parents for the next generation.
• It ensures desirable genes are passed on.

Selection Methods

• Individual Selection: Focuses on the individual animal's performance, most effective for traits with high heritability.
• Family Selection: Considers the average performance of a family, useful for traits with low heritability.
• Pedigree Selection: Choosing breeding animals based on their ancestors' performance.
• Progeny Testing: Evaluates an individual's breeding value based on its offspring's performance; especially helpful for traits observed after breeding or those restricted by sex.

Breeding Systems

• Breeding systems involve mating animals to achieve specific genetic outcomes.
• Example breeding systems include: outbreeding (outcrossing and crossbreeding), inbreeding, and species hybridization.

Outbreeding

• Animals that are not closely related are bred.
• Outcrossing: Mating animals that aren't closely related within the same breed.
• Crossbreeding: Mating animals from different breeds; can exploit heterosis (hybrid vigor).

Inbreeding

• Involves mating closely related animals.
• Increases homozygosity (having identical alleles) of the population.
• Often leads to inbreeding depression (reduced fitness).

Species Hybridization

• Different species interbreed.
• Results in hybrid offspring.
• Can lead to new traits, adaptations, and in some cases, new species.

Genetic Control of Farm Animal Traits and Inherited Disorders

Phenotypic Traits

• Qualitative: Classical Mendelian traits under strong genetic control, little environmental influence. Examples include form, structures, antigens, and antibodies.
• Quantitative: Measurable traits strongly affected by both genetic and environmental factors. Examples include milk production, meat yield, height, and weight.

Management and Control of Inherited Diseases

• Genetic Screening and Breeding Management:
  • Screening
  • Selective Breeding
• Early Diagnosis and Identification of At-Risk Animals:
  • Health Monitoring
  • Management of Carrier Animals
• Medical Management and Disease Control:
  • Vaccination
  • Medication
• Regular Monitoring and Health Tracking:
  • Routine Health Checks
  • Record Keeping

Inherited Disorders in Farm Animals

• Widespread use of artificial insemination and international semen trading spreads undesirable genes.
• Most common inheritance pattern for genetic diseases is autosomal recessive.

Autosomal Recessive Inheritance

• An individual must inherit two copies of a defective gene (one from each parent) to express the disorder.
• Specific examples like Bovine Brachyspina Syndrome (BBS), Bovine Leukocyte Adhesion Deficiency (BLAD), and Porcine Stress Syndrome (PSS) are highlighted.

Control of Single Gene and Multifactorial Disorders by Selection and Breeding

Single Gene (Mendelian) Disorders

• Mutations in a single gene create these disorders, with diverse inheritance patterns:
  • Autosomal Dominant: Mutation in one gene copy causes the disorder.
  • Autosomal Recessive: Both gene copies must be mutated for the disorder to appear.
  • X-Linked: Disorders linked to mutations on the X chromosome.

Breeding and Selection for Single-Gene Disorders

• Effective breeding programs are facilitated by genetic testing allowing breeders to:
  • Identify carriers
  • Avoid affected individuals
  • Use genetic testing as a preventative tool

Multifactorial Disorders

• Disorders influenced by multiple genes and environmental factors.
• Specific example disorders mentioned include diabetes, heart disease, and cleft palate.

Breeding and Selection for Multifactorial Disorders

• Breeders aim to reduce the risk by:
  • Selecting individuals with fewer risk alleles.
  • In the absence of precise genetic markers, selecting based on observable traits or health outcomes, and
  • Managing environmental factors affecting animals.

Non-genetic (Environmental) Control of Inherited Disorders

Environmental Factors

• Environmental factors influence whether a genetically predisposed condition is expressed, including factors like nutrition, housing, and management practices.

1. Nutrition

• Balanced diets are essential for optimal growth and health.
• Poor nutrition can induce previously dormant genetic disorders.
• Examples include nutritional disorders in livestock.

2. Management Practices

• Stress can exacerbate genetic predispositions.
• Stress lowers the animal's immune response.
• Management practices (e.g., housing conditions, handling techniques) should minimize stress.

Types of Mating Systems In Sexual Animals

• Monogamy: Single male with a single female; both contribute to defense and offspring care.
• Polygamy: One male breeds with multiple females.
  • Resource defense
  • Male dominance
  • Harems
  • Lek
• Promiscuity: Both males and females have multiple mates.
• Polyandry: One female breeds with multiple males; multiple males often contribute to care and provisioning.
• Polygynandry: Multiple females and males mate with each other; males may care for several females' offspring.

Selection of Phenotypes

• Phenotypes are observable traits resulting from gene-environment interactions.
• Physical characteristics and other observable traits are included in this process.

Phenotypic Selection

• Individuals with different traits differ in survival/reproduction.
• Phenotypic selection is nonrandom differential survival/reproduction of individuals.

Types of Selection

• Stabilizing selection: Favors an average phenotype. Selection against extreme phenotypes.
• Directional selection: Phenotypes at one end of the spectrum are favored. Selection caused by environment changes.
• Diversifying selection: Phenotypes at opposite extremes are favored. Intermediate forms have lower fitness.