Genetics

Genetic Traits in Horses

• Traits in horses can be dominant or not, impacting breeding outcomes.

  • Dominant traits tend to prevail in offspring.

  • Incomplete dominance can occur, where traits blend together (e.g., red and white to produce roan horses).

Genetic Disorders

• Genetic disorders exist within horse breeds, affected by recessive genes.

  • HYPP (Hyperkalemic Periodic Paralysis): A disorder in horses where potassium cannot move in and out of cells effectively.

    • Symptoms include muscle spasms and weakness triggered by stress or exercise.

    • This disorder is associated with the "Impressive" bloodline of Quarter Horses.

• Inbreeding increases the likelihood of expressing recessive genes that lead to disorders.

Breeding and Genetic Considerations

• Breeding requires understanding the risks of genetic abnormalities and disorders.

  • Altering breeding pairs (i.e., outcrossing) is one method to reduce risks of inherited disorders.

  • Record keeping is vital to track bloodlines and potential hereditary issues.

Advancements in Genetic Science

• Genetic mapping in horses has improved understanding of hereditary traits.

  • Researchers can identify specific segments in DNA associated with traits through genomics.

  • Genetic testing (e.g., through hair and blood samples) provides breeding insights and helps predict outcomes:

    • Certain traits can be tied to genetic markers or "snips" in the DNA sequence.

Hormonal Influence on Reproduction

• Male hormones (mainly testosterone) are crucial for sperm production and overall behavior.

  • Testicles produce sperm and hormones and must remain at a cooler temperature than the body.

  • Cremaster Muscle: Regulates the position of testicles based on temperature, drawing them closer in cold and further away in heat.

Sperm Production Process

• Male puberty occurs around 15 months of age, but optimal breeding usually starts around 3 years.

• A typical ejaculation contains millions of sperm necessary for successful fertilization.

• Sperm undergo different stages of development:

  • Meiosis: Process of halving chromosome numbers to create gametes (sperm).

  • Spermatogenesis: Final stage of sperm maturation, including developing tails and heads.

Sperm Transport and Accessibility

• Sperm travels from testicles through the epididymis and vas deferens.

  • Sperm can remain viable in the female reproductive tract for days, helping ensure successful fertilization within a narrow window.

Understanding Genetic Abnormalities in Horses

• Genetic abnormalities can lead to severe health issues or fail to produce viable offspring (e.g., failed pregnancies).

  • Abnormalities can stem from recessive traits when inbreeding occurs.

  • As awareness of breeding implications grows, ethical breeding practices are increasingly emphasized.