Harmful effects of selective breeding

Interbreeding
1. Well known that pedigree dogs typically have a shorter life expectancy and worse health than that of their cross-bred counterparts - pedigree dogs are more in-bred
  1. Cross bred animals have a higher chance of displaying "hybrid vigor" - making them more functional due to beneficial (diverse) genetic contributions from both parents
2. Breeds displaying a severe prevalence of inherited conditions are often descended from very few animals = small founding
  1. KCCS - Thought to descend from only 6 dogs
    1. Rusbridge and Knowler, 2003
3. Line breeding
  1. Commonly practiced in the dog breeding community - keeping lines "pure" by continually mating a handful of successful animals which share a common ancestor = greater chance of replicating desirable characteristics
  2. Line breeding reduces genetic variability and prevents hybrid vigor from occuring in most matings
    1. Using popular sires also dramatically reduces genetic variability
  3. Due to line breeding, of the 45,000 Boxers surveyed in the UK, all could be traced back to only 45 breeding dogs
    1. Calboli et al., 2008
  4. Often, by selecting for a select gene another seemingly un-related gene is also promoted - Dalmatians black patches promotes high uric acid that can contribute to urinary disorders
4. Out-crossing to increase genetic variability and reduce heritable conditions
  1. For example: Dalmatian out crossed with a Pointer, then back in to Dalmatians that didn't have a heritable disorder (high uric acid) = progeny without genetics for the disorder
    1. The KC will only register the 5th generation of these out-crosses however = breeders are put off
      1. Rooney and Sargan, 2009
Many perspective owners will buy dogs based on their pedigree - believing it indicates quality = promotes further pedigree breeding
Morphological extremes
1. Large head - dystocia
  1. C-section often required
    1. Females have no limitations on number of C-sections allowed
2. Short legs & long backs - limited locomotion & predisposition to spinal issues
  1. Disc prolapse & subsequent spinal cord compression - pain, weak back legs & eventual paralysis
    1. Singh and Masuda, 2005
3. Large, heavy set breeds - joint issues
  1. Osteochondrosis - death of bone cells growing too quickly for blood supply to function effectivly
    1. Limits mobility - lameness from an early age
    2. Can cause secondary damage - often permanent
    3. PAINFUL.
    4. Ekman and Carlson, 1998
  2. Hip/ elbow dysplasia
    1. Malfitting of bones into joints and surrounding tissue too weak to hold in place- erosive change of joint/ dislocation occurs
      1. PAINFUL - often progressive through the creation of arthritis
4. Brachycephalic - respiratory issues
  1. Elongated soft palette interferes with air passage into the trachea
    1. Monet, 2004
  2. Dogs commonly cause secondary damage to larynx when attempting to breath (forced) which can lead to laryngeal collapse
  3. Stenotic nares- shortening of the nostrils reduces air inspired
  4. Surgical opening of the nostrils and ressection of soft palate VERY common to allow for more normal exercise
  5. Reduced area for evaporation when panting - prone to heat stroke
    1. Bruchim et al., 2006
5. Skin folds - dermatitis, bacterial infection & inflammation
6. Toy breeds
  1. Prone to stress fractures from minimal trauma - eg jumping up and down
  2. Patella luxation common - pain & lameness
7. "Neotenous facial features" - Puppy face in adulthood (KCCS/ Pomeranian)
  1. Incomplete development of skull - predisposes to syringiomyelia
    1. Under-developed skull = disrupts cerebrospinal fluid causing accumulation & cyst formation - cyst can grow over time causing damage to spinal cord
      1. Headaches, weakness, referred pain, stiffness and paralysis
        Rusbridge, 2005
    2. Can also be a heritable condition
8. Curved tails predispose to curvature of the spine
  1. Hind limb weakness
  2. Paralysis
  3. Faecal/ urinary incontinence
Morphological extremes that affect behaviour
1. Hungarian Puli - hair covers eyes
  1. Cannot see as well therefore more likely to react aggressivly / be unaware of surroundings due to its lack of context
2. Brachycephalic/ Short legged
  1. Ability to move/ exercise is limited - difficulties in play, exercise and normal dog interactions
  2. Less able to show facial expressions - lack of signalling
3. Toy breeds
  1. Due to their size they often suffer from high levels of fear/ defensive behaviours
    1. Duffy et al., 2008

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Harmful effects of selective breeding

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