ANSC 306 (EXAM 4): Lecture 1-Genetic Diseases Responsible Breeding

What does Hyperkalemic Periodic Paralysis (HYPP) primarily affect in horses?

It is a muscular disease that disrupts ion channels, leading to excess potassium in the blood and excess sodium in muscle cells.

What is the inheritance pattern of HYPP?

Autosomal dominant; only one allele is needed for the disease to manifest.

How does the severity of HYPP differ between homozygous and heterozygous horses?

Homozygotes are typically more severely affected than heterozygotes.

What are common clinical signs of an HYPP episode?

Muscle tremors, spasms, weakness, sweating, third eyelid prolapse, noisy or labored breathing, paralysis, collapse, and death.

What environmental factors often trigger HYPP episodes?

Stress is a common trigger for clinical signs.

What are the dietary management goals for a horse with HYPP?

Avoid high-potassium feeds (e.g., alfalfa, brome, soybean meal, molasses) and maintain a diet with less than 5% total potassium.

Which specific horse breed and family line is famously associated with HYPP?

The 'Impressive' bloodline in American Quarter Horses.

What is the approximate carrier rate of HYPP in the AQHA population?

4.4 to 5% of the general AQHA population, but over 50% of the halter horse population.

What does MYHM stand for in the context of equine genetic diseases?

Myosin-Heavy Chain Myopathy.

What is the inheritance pattern of MYHM?

Autosomal dominant with variable penetrance.

What are the two distinct clinical presentations of MYHM?

Immune-mediated myositis (IMM) and non-exertional rhabdomyolysis.

What triggers the immune system to cause muscle disease in MYHM-affected horses?

Certain illnesses or vaccinations (where the needle exposes muscle proteins to the immune system).

What are the symptoms of the non-exertional rhabdomyolysis form of MYHM?

Stiffness, swelling of muscles along the back and haunches, and difficulty rising.

What is the definition of selective breeding in horses?

Selective breeding is the practice of directed evolution, where humans choose specific parents to influence the traits of future generations.

What are some common reasons horse owners decide to breed their horses?

To produce a specific performance horse, to continue a bloodline, for personal companionship, or for commercial sale.

What parameters should be considered when selecting breeding stock?

Genetic health, temperament, conformation, performance history, and the overall purpose of the foal.

What are some general best practices for responsible horse breeding?

Genetic testing for known diseases, evaluating the necessity of breeding, and ensuring the long-term welfare of the offspring.

What makes a horse 'unwanted'?

A horse is considered unwanted when it is no longer wanted by its current owner due to age, health, performance issues, or the owner's financial/personal circumstances.

What are some common misdiagnoses for HYPP episodes?

Tying up, colic, and choke.

Are all horses with the HYPP genetic mutation symptomatic?

No, some affected horses show no signs at all or have only one or two episodes in their lifetime.

What types of hay are preferred for horses with HYPP?

Later cuts of timothy, oat, or bermudagrass hay.

What is the primary physiological defect in IMM (a form of MYHM)?

Acute epaxial and gluteal muscle atrophy or damage.

Which breeds are primarily associated with MYHM?

Quarter Horses and related breeds, specifically linked to the Peppy San Badger bloodline.

What is the duration of clinical signs during an HYPP episode?

The duration varies from minutes to hours.

Why is regular exercise important for horses with HYPP?

Frequent access to turnout and regular exercise helps manage the condition and reduces the likelihood of severe episodes.

What is a common trigger for Myosin-Heavy Chain Myopathy (MYHM)?

Strangles vaccine or infection.

What are the initial clinical signs of MYHM?

Stiffness, weakness, and decreased appetite.

What is the age risk profile for developing Immune-Mediated Myositis (IMM)?

Horses less than 8 years old or greater than 17 years old.

What percentage of horses that develop IMM experience a reoccurrence?

50%.

What condition do some horses develop after recovering from non-exertional rhabdomyolysis?

Immune-Mediated Myositis (IMM).

What does the acronym HERDA stand for?

Hereditary equine regional dermal asthenia.

What is the inheritance pattern of HERDA?

Autosomal recessive.

What are the primary clinical signs of HERDA?

Loose, stretchable, hyperextensible skin, fragile skin that sloughs, and disfiguring scars.

At what age are HERDA signs typically identified?

Approximately 18-24 months of age, though some may not show lesions until 4+ years.

How does the skin of a horse with HERDA compare to a normal horse?

It is 2-5 times more stretchable.

Besides skin, what other tissues can be affected by HERDA?

Cornea, great vessels, tendinoligamentous structures, and heart valves.

What is the recommended management for a horse with HERDA?

Minimize trauma, avoid group turnout, protect from insect bites, eliminate rubbing surfaces, remove obstacles, and restrict from training.

Which nutritional supplements are recommended for managing HERDA?

Copper, Zinc, Vitamin C, and Omega-3 fatty acids.

To which Quarter Horse stallion is the HERDA mutation traced?

Poco Bueno (1944).

What is the estimated carrier frequency of HERDA in the overall Quarter Horse population?

3.8%.

What is the estimated carrier frequency of HERDA in elite cutting horses?

Approximately 28.3%.

What does the acronym OLWS stand for?

Overo Lethal White Syndrome.

What is the inheritance pattern of OLWS?

Autosomal recessive.

What are the physical characteristics of a foal born with OLWS?

All white coat, pink skin, and blue eyes.

What physiological defect causes the death of foals with OLWS?

A lack of ganglion nerves in the intestines.

How quickly do foals with OLWS typically show signs of colic?

Within 12 hours of birth.

What percentage of frame overo horses carry the OLWS gene?

Greater than 94%.

Can a horse without white markings carry the OLWS gene?

Yes, horses of overo lineage without white markings can still carry the gene.

Which genetic tests are required for AQHA breeding stallions?

HYPP, PSSM, MH, GBED, HERDA, and MYHM.

Which genetic tests are required for APHA breeding stallions?

HYPP, PSSM, MH, HERDA, and OLWS.

Which five genetic conditions must APHA breeding stallions be tested for?

HYPP, PSSM, MH, HERDA, and OLWS.

Does the Arabian Association require genetic testing for stallions?

No, they have no genetic testing requirement for stallions.

How is breeding defined in the context of animal husbandry?

Choosing individuals expected to have offspring with desirable properties.

In artificial breeding, how is 'fitness' defined?

Fitness is defined by the breeder rather than by the individual's ability to survive and reproduce in nature.

What is the primary role of breeding in the horse industry?

Refining breeds, ensuring they meet intended use demands, and preserving unique traits, heritage, and cultural identities.

How is a 'wanted' horse defined in the context of the 2023 NAHMS survey?

A horse that is not unwanted by its current owner due to age, injury, sickness, unmanageability, failure to meet expectations, or financial constraints.

What is the goal of the 'Full Circle' program?

To encourage individuals to provide a 'forever home' for horses.

What is a common saying regarding the responsibility of owning livestock?

If you have livestock, you also have deadstock.

List four factors considered during breeding stock selection.

Conformation, health, athletic ability, and performance history.

What is the fundamental rule regarding which horses should reproduce?

Not all horses should reproduce.

What is the primary goal of a responsible breeder when selecting mates?

To breed quality individuals with the goal of producing an even higher quality individual.

What must a breeder ensure regarding a mare's physical health before breeding?

That she is healthy enough to withstand the stress of pregnancy and foaling.

What is a key ethical guideline regarding genetic disease in breeding?

Do not breed to genetic disease carriers.

What is a critical consideration for a breeder regarding the foal's future?

Develop a functional plan B if the plan A is to keep the foal 'forever'.

What is the warning regarding the risk of breeding a specific mare?

Don't breed her if you don't want to lose her.

What are the five key areas responsible breeders evaluate in potential breeding stock?

Conformation, disposition, pedigree, performance, and health.

What is the purpose of genetic disease testing in breeding programs?

To identify and limit the transmission of harmful genetic traits within the breed.

Why is 'disposition' a critical factor in breeding?

To ensure the offspring have a temperament suitable for their intended use and safety.

What is the breeder's obligation regarding the 'entire life cycle' of offspring?

To think about and plan for the long-term welfare of the offspring throughout their entire life.

What is the consequence of selecting for specific traits in horse breeding?

It plays a pivotal role in refining the breed and ensuring adaptability.

What is one reason people might incorrectly choose to breed a mare?

To 'settle her down' or because 'every mare deserves to have at least one foal'.

What is a common misconception about breeding horses for profit?

That it is an easy way to make money, ignoring the costs of health, training, and the risk of not being able to sell the foal.

What does the term 'unwanted' imply for a horse?

The horse is no longer wanted by its current owner due to factors like injury, old age, or failure to meet performance expectations.

What is the breeder's responsibility regarding the foal's training?

To ensure the foal is properly trained and socialized.

What is the ultimate goal of responsible breeding regarding the breed's future?

To improve the health, athleticism, and adaptability of the breed.

What is the primary difference in disease expression between autosomal dominant and autosomal recessive traits?

Autosomal dominant requires only one allele for expression, while autosomal recessive requires two copies (homozygous recessive) for expression.

How does the severity of disease expression differ between homozygotes and heterozygotes in autosomal dominant conditions?

Homozygotes are typically more severely affected than heterozygotes.

Which four equine diseases are classified as autosomal dominant?

HYPP, MYHM, MH, and PSSM1.

Which four equine diseases are classified as autosomal recessive?

HERDA (Hereditary Equine regional dermal asthenia)

SCID (Severe combined immunodeficiency)

OLWS (Overo lethal white syndrome)

GBED (Glycogen branching enzyme deficiency)

What is the physiologic defect associated with HYPP?

A mutation disrupts the sodium ion channel, leading to excess potassium in the blood and excess sodium in muscle cells.

What are common clinical signs of an HYPP episode?

Muscle tremors/spasms, weakness, sweating, 3rd eyelid prolapse, noisy/labored breathing, and potential paralysis leading to collapse or death.

What dietary management strategy is recommended for horses with HYPP?

Avoid high-potassium feeds (e.g., alfalfa, brome, soybean meal, molasses) and prioritize timothy, oat, or bermuda hay.

Why is regular exercise beneficial for horses with HYPP?

Adrenaline produced during exercise helps move potassium into the cells, reducing blood potassium levels.

What is the physiologic defect in MYHM (Myosin Heavy Chain Myopathy)?

A mutation in the myosin heavy chain isoform 1 in Type IIX muscle fibers, which requires immune system triggers to activate.

What are the two primary clinical presentations of MYHM?

Immune-Mediated Myositis (IMM) and non-exertional rhabdomyolysis.

What characterizes the IMM presentation of MYHM?

Acute epaxial and gluteal muscle atrophy, with up to 40% muscle loss occurring within 72 hours.

What is the primary physiologic defect in HERDA?

A collagen defect that makes the skin 2 to 5 times weaker than that of a normal horse.

At what age or life stage do HERDA lesions typically appear?

Lesions often appear between 18-24 months of age or when the horse is first saddled for training.

What is the physiologic cause of Overo Lethal White Syndrome (OLWS)?

Foals lack intestinal ganglion nerves, resulting in a total lack of peristalsis.

What are the classic clinical signs of a foal with OLWS?

All-white coat, pink skin, blue eyes, and onset of colic within 12 hours of birth, leading to death within a few days.

What is the definition of selective breeding in the context of equine management?

Choosing individuals expected to produce offspring with desirable traits, often described as 'directed evolution' where fitness is defined by the breeder.

What are three primary purposes of selective breeding?

To improve health, athleticism, and adaptability, and to preserve breed identity and heritage.

What defines an 'unwanted' horse?

A horse that is old, injured, sick, unmanageable, fails to meet performance/color expectations, or is owned by someone who can no longer afford its care.

What is the current status of the 'unwanted horse' issue in the North American equine industry?

It is ranked as the number one welfare concern according to the 2023 NAHMS survey.

What are the key criteria for selecting breeding stock?

Soundness, conformation, health, athletic ability, performance history, disposition, and pedigree.

What is the 'key message' regarding the decision to breed horses?

Not all horses should reproduce.

What are three responsible breeding practices mentioned in the text?

Performing genetic testing, avoiding breeding carriers to carriers, and having a plan for the foal's entire life cycle.

What is a major consideration regarding the financial reality of breeding?

The cost of keeping a foal alive and trained, the risk of it not selling, and the reality that 'if you have livestock, you also have deadstock.'