What is the difference between inbreeding and line breeding? Actually not much….Line breeding, in itself is inbreeding, we softened the name to make it more acceptable to our ears. Many of us have been taught that inbreeding is breeding very closely related animals, such as Father to Daughter, Brother to Sister. Line breeding, as we were taught, is breeding Grandsire to Grand daughter, etc. Needless to say, people will have their own opinions on what is considered inbreeding and line breeding. But technically, unless you outbreed, you are in fact inbreeding on some level.
- Lower fertility
- Lower “vigor”
- Birth defects
- Smaller size
- Fewer offspring
- Slower growth
- Higher offspring mortality
- Shorter lifespan
- Increase in genetic diseases
- Reduced “genetic potential” (ability to improve a trait)
- Increased uniformity
- Increased prepotency (ability to pass on traits to offspring)
- “Fixing” of desired traits and breed type
Notice how short the list of ‘advantages’ are when compared to the disadvantages? Seriously, during our studies we were very surprised to find what we found. Namely, that “90% of unique genetic variants are LOST over six generations, indicating a dramatic effect of breeding patterns on genetic diversity”[iii]
Line breeding and inbreeding is a necessary practice when you start a new species or breed. It is impossible to start a new species or breed without it. However there is a time when the continued practice could, and has, destroyed a line completely.
Now let’s point out that if you have Kinder goats, you most likely have goats that have been either line bred or inbred at some point. Let’s also note that Sue Bowling explains that the term inbreeding is ‘not generally used to refer to matings where a common ancestor does not occur within a 5 generation pedigree’.
Now let’s look at the term Homozygous that you will find in any research you do on inbreeding and line breeding. Homozygous means having identical pairs of genes for any given pair of hereditary characteristics. So let’s look at an example….you have two goats that have trait, such as build, color, size, etc. By using inbreeding/line breeding you increase the chances of that trait being passed to the offspring.
What people need to also understand is that there are thousands of genes that make up any animal, plant, and human. For all the visible traits that we can see, there are many, many, more that exist that are beyond our sight. It’s these ‘recessive’ genes that cause the problems. All these issues that have appeared in so many breeds and species are because they remained hidden until it was too late. Here is just a SMALL sampling of them:
- Addison’s disease in Portuguese Water Dogs[iv]
- Interstitial lung disease in West Highland White Terriers[v]
- Canine Narcolepsy[vi]
- Patent ductus arteriosus (PDA)[vii]
- Lethal chondrodysplasia in a family of Holstein cattle[viii]
- Deleterious recessive allele in the endangered Scottish chough (Pyrrhocoraz pyrrhocorax)[ix]
- Tuberculosis in Red Deer (Cervus elaphus)[x]
- Progressive retinal atrophy[xi]
Now let’s talk about another term you are likely to hear if you research inbreeding/line breeding…..Coefficients. We aren’t going into a ton of information, just the basics. Pearl[xii] published a number of papers regarding the subject and calculations. Pearl came up with the first formula for the ‘risk’ factors associated with the practice. Pearl’s calculations were limited, they did not show the factors for multiple generation. Pearl’s research showed that problems did arise with the practice. Later, Dr. Sewell Wright[xiii] expanded on this, saying that multiple generations needed to be taken into account to show the true coefficient numbers. Wright stated in his paper that “If an individual is inbred, his sire and dam are connected in the pedigree by lines of descent from a common ancestor or ancestors”. He further showed that the total for every line the parents are connected needed to be taken into consideration. Studies done at Cornell University by Dr. John Pollock showed that health and productivity problems increased as the COI (Coefficient) rose beyond 9%. [xiv] Now think about this, breeding half-siblings is at a coefficient of 25%, breeding Parent to offspring is a coefficient of 50%. You can see where this is going can’t you?
As Kinder breeders, we are lucky. Yes lucky! We have a chance to use the experience of this research, as well as the problems proven by other species to change our mind set and make better choices for breeding our Kinders. We have a chance to expand on a gene pool that, in itself, is limited.
We, ourselves, have seen patterns in our own goats that correspond with the list of disadvantages. Just one example on offspring numbers will show you that. With our outbreed does we have had 1 single birth, 4 sets of twins, 3 sets of triplets, and 2 sets of quads. Our line breed does have given us only singles and twins. Also, in the many years we have been breeding, we have had only 2 bucks that we kept intact and neither could be registered. This is the first year we have had registered bucks of good quality – in fact 4! What changed? New blood lines! We have does not closely related to our other does and a buck that isn’t related to any of our other stock. How’s that for perspective?
We have seen how the disadvantages have been proving correct. We also have our own personal experiences to show us. We need to STOP and think about our breeding practices and use the research and experience of other species to make better choices for ourselves and our Kinders.
So what we’ve decided? Unless we have NO choice, we are NOT going to line breed and we will NEVER inbreed!
“…the breeding of purebred dogs is akin to [breeding laboratory mice]…[most breeds] are becoming progressively more inbred. My observation is that most are on the road to extinction, but most breeders do not even realize they are part of an experiment”.
~John B Armstrong, PhD
Nick & Brenda Lee
[i] The Institute of Canine Biology; http://www/instituteofcaninebiology.org/blog/the-costs-and-benefits-of-inbreeding
[ii] The Institute of Canine Biology; http://www/instituteofcaninebiology.org/blog/the-costs-and-benefits-of-inbreeding
[iii] “Population Structure and Inbreeding from Pedigree Analysis of Purebred Dogs”; US National Library of Medicine National Institutes of Health; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2390636/
[iv] Understanding the genetics of autoimmune disease: two loci that regulate late onset Addison’s disease in Portuguese Water Dogs; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775482/
[v] Interstitial lung disease in West Highland White Terriers; http://www.ncbi.nlm.nih.gov/pubmed/15657270
[vi] The sleep disorder canine narcolepsy is caused by a mutation in the hypocretin (orexin) receptor 2 gene; http://www.ncbi.nlm.nih.gov/pubmed/10458611
[vii] Epidemiology, presentation and population genetics of patent ductus arteriosus (PDA) in the Dutch Stabyhoun dog; http://www.ncbi.nlm.nih.gov/pubmed/27297070
[viii] Lethal chondrodysplasia in a family of Holstein cattle is associated with a de novo splice site variant of COL2A1; http://www.ncbi.nlm.nih.gov/pubmed/27296271
[ix] A bird's eye view of a deleterious recessive allele; http://www.ncbi.nlm.nih.gov/pubmed/27279331
[x] Tuberculosis, genetic diversity and fitness in the red deer, Cervus elaphus; http://www.ncbi.nlm.nih.gov/pubmed/27245150
[xi][Progressive retinal atrophy; http://www.eyevet.ca/pra.html
[xii] American Naturalist, 1917, 51: 545-559; 51: 636-639
[xiii] Coefficients of Inbreeding and Relationship; Dr. Sewall Wright; Bureau of Animal Industry, US Department of Agriculture
[xiv] Why Incest Isn’t Best, By C.A. Sharp; first published in Australian Shepherd Journal, Nov/Dec. 2002