Lecture 7: Physical health and disease

Why do purebred dogs often suffer from health problems?

Because modern dog breeds were formed from small founder populations with strong selection for physical traits (e.g. color, size), causing high inbreeding and accumulation of harmful genetic variants.
Example: Bulldogs often suffer from breathing issues due to their shortened snouts.

What is inbreeding depression in dogs?

The reduction in health and fitness due to breeding within a limited gene pool, increasing the expression of harmful recessive traits.
Example: Hip dysplasia and epilepsy are more common in inbred lines.

What is the purpose of genetic mapping in dogs?

To identify disease-causing variants and understand inheritance patterns. Methods include association studies (population-based) and linkage analysis (family-based).

What are some common health issues found in purebred dogs, and why do they occur?

Selective breeding for appearance (morphology, size, color) has reduced genetic diversity in purebred dogs, leading to inherited health problems. Common issues include:

• Hip dysplasia: Poor hip joint formation, common in large breeds like German Shepherds.

• Breathing problems: Seen in Bulldogs due to shortened snouts (brachycephalic traits).

• Epilepsy: More frequent in some purebred lines because of hereditary neurological predispositions.

• Heart defects: Certain breeds are genetically more prone.

• Eye problems: Beagles often develop glaucoma; Pugs suffer from eye injuries due to facial structure.

• Bloat (gastric torsion): Common in deep-chested breeds like Boxers.

• Skin and ear infections: Breeds with wrinkled skin or floppy ears, such as Bloodhounds, are especially susceptible.

How are genetic risk factors identified for canine diseases?

Through two main methods:

• Association studies (GWAS): Compare DNA from unrelated affected and healthy dogs to find variants linked to disease.

• Linkage analysis: Uses family pedigrees to track how diseases and genetic markers are inherited together.

Both methods can locate genes for monogenic (single-gene) and complex diseases.

Example: The same mapping techniques used for coat color genes can identify mutations causing inherited disorders.

What are antigens and antibodies, and how do they work together?

• An antigen is a foreign substance (like bacteria, viruses, or toxins) that triggers an immune response.

• Antibodies, produced by B cells, bind specifically to these antigens and help immune cells destroy them.

• When an antigen activates a B cell, it divides into plasma cells that release millions of antibodies into the blood and lymph system.

Example: When a virus enters the body, antibodies attach to it so immune cells can recognize and eliminate it.

How is pain assessed in rabbits?

Through behavior-based scoring systems that quantify signs of distress, now widely used to improve welfare assessment.

What is the “Ridden Horse Pain Ethogram” (RHpE)?

A list of 24 specific behaviors that indicate pain in horses during riding, such as pinned ears, tail swishing, or resistance to rein cues.
Example: A horse showing head tossing or refusing jumps may be in discomfort.

Why is identifying pain in ridden horses difficult?

Because rider cues (e.g. rein tension, leg pressure) can influence horse behavior and mask signs of pain. Also, emotional stress or confusion may mimic pain behaviors.

What are “conflict behaviors” in horses?

Behaviors that arise from contradictory signals or frustration rather than pain itself, such as anxiety when separated from herd mates.

What is the immune system’s main function?

It defends the body against pathogens and cancer by identifying and eliminating foreign invaders like bacteria, viruses, and parasites.

What is the difference between the innate and adaptive immune systems?

• Innate: Immediate, non-specific defense (skin, phagocytes).

• Adaptive: Specific, slower response that forms memory for future protection.
  Example: Vaccination works by activating the adaptive system.

What is ELISA used for?

(Enzyme-Linked ImmunoSorbent Assay)

A biochemical test that detects and measures antibodies, antigens, proteins, or hormones based on antigen-antibody binding.
Example: ELISA is used in pregnancy tests and disease diagnostics.

How do hormones like cortisol and adrenaline affect immunity?

• Cortisol (a glucocorticoid) suppresses the immune system by reducing T cell activation and proliferation, weakening adaptive immunity and lowering vaccine effectiveness.

• Adrenaline and noradrenaline can boost innate immunity (e.g. macrophage activity) but may inhibit adaptive immunity by altering T and B cell function.

The effects depend on context, such as whether the stress is acute or chronic.

What happens to the immune system during acute stress?

It temporarily boosts immunity (“fight or flight” mode) by mobilizing immune cells and producing pro-inflammatory cytokines to handle immediate threats.
Example: A short chase can make immune cells more active in an animal.

What happens during chronic stress?

It suppresses adaptive immunity, reducing T and B cell activity and increasing susceptibility to infections.
Example: Farm animals kept in crowded or unstable groups show weaker vaccination responses.

What did studies in mice show about stress and immunity?

• Acute stress increased norepinephrine, which boosted macrophage activity but suppressed T cell activation.

• Chronic stress reduced B cell function and weakened antibody responses, showing long-term harm to humoral immunity.

Overall, acute stress can temporarily enhance immunity, while chronic stress leads to immune suppression.

What is the role of the microbiome in immunity?

Gut microbes help train and regulate both innate and adaptive immune systems. Disruption (by stress or antibiotics) can cause inflammation or autoimmune issues. 

How does social stress affect farm animals?

• Social stress alters lymphocyte levels, natural killer (NK) cell activity, and vaccine responses.

• High stocking density increases pathogen transmission.

• Individual animals react differently — e.g. cows with high cortisol after isolation showed stronger fever responses to infection a year later.

• Pigs with different escape behaviors showed varied immune changes after stress.

How does biosecurity and stress interact in real farm environments?

• Farm animals often face multiple, overlapping stressors that vary in intensity and duration.

• Natural pathogen exposure involves complex interactions between different pathogens.

• Real-world stress is more variable and intense than in controlled experiments, making immune responses harder to predict.

(Biosecurity: Actions taken to protect animals from diseases and prevent infection spread.)

How does pasture access affect dairy cattle health?

It reduces some diseases (like mastitis and hoof issues) but increases risk of parasites and malnutrition. Balancing welfare and biosecurity is key.

How does urbanization impact animal health?

It increases exposure to toxins, parasites, and stressors such as light and noise pollution, negatively affecting physiology and reproduction.

What did the house sparrow study reveal about noise pollution?

Birds nesting near generators had fewer and weaker offspring. Noise reduced parental feeding rates, confirming stress and reproductive costs.

What were the results of the “City Sicker?” meta-analysis?

Urban wildlife generally had higher toxicant loads, parasite levels, and stress compared to non-urban animals, especially invertebrates and amphibians.

What factors determine an animal’s likelihood of disease?

1. Human selection (morphology, genetics)

2. Human interaction (handling, stress)

3. Environmental conditions (natural vs artificial habitats)