Keeping Aware of Potential Genetic Defects
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As breeders well know, genetics play a huge role in a herd’s success, especially when trying to make improvements. Even with wise breeding decisions and top-quality animals, the road to development can be long and frustrating. Fortunately, most matings are not detrimental to the resulting kids, nor do they typically cause too significant of a setback in genetic progress.
However, genetic defects and hereditary diseases can occur in a small percentage when certain traits are passed along in a mating. A recessive trait can get passed along through the generations only to rear its head quite unexpectedly. There can also be mutations or changes in genetic makeup during the early development stages.
Where it all begins
Let’s take a look at the roots of genetic issues. Understanding how traits pass and how defects originate can be beneficial when scrutinizing the breeding stock chosen to impact your herd.
Offspring receive one trait of a gene from each parent. Bucks and does pass along traits that can impact the offspring depending on what one gene passes from each parent. Inherited defects resulting from mutant genes present in breeding lines may be expressed in typical patterns of inheritance. There are also dominant defect traits that are inherited as well.
A congenital defect is a development disruption noticeable at birth, but some genetic defects can appear later in life. Some defects that occur later could have been from a disruption before birth (this is not considered congenital).
There have been advancements in identifying many specific genetic, environmental, and infectious agents. The advent of genetic testing has been an enormous benefit to aid breeders in testing animals to try and help identify potential undesired traits, but not all of them can be wholly accounted for.
Some issues occur within specific breeds or types. For example, a prevalent inherited defect within Nubians is the G6-Sulfatase deficiency — a metabolic defect. The cause of this undesired defect is a mutation that renders the enzyme incapable of degrading complex polysaccharides. This deficiency affects how the animal digests food and affects their overall growth and development, and early death can be an expensive loss.
Some symptoms for genetic defects, like the G6-Sulfatase, can include failure to grow in addition to a smaller kid at parturition and then maturing slower. Immune function can also appear to be compromised.
A doe with one or more male littermates may be sterile in rare cases — known as a freemartin. This condition, essentially caused by the doe’s exposure to male hormones leading to an underdeveloped reproductive tract, is widespread in cattle but extremely unlikely in goats (some say as low as 1% or less of all does).
Congenital arthrogryposis affects the kid’s joints and structural development explicitly. As the name implies, it is congenital, making it distinguishable at birth.
Some congenital issues appear randomly and range from minor oddities that don’t interfere with the quality of life to very serious or even deadly ones. These are severe teat deformities that interfere with milking or nursing, hermaphrodites (intersex), and atresia ani (born without an anus).
Pay close attention to matings that result in these types of issues. Do not repeat the buck/doe pairing that resulted in them. If a single buck or doe continually has these issues with different mates, they should be culled or retired from the breeding program.
DNA tests can be expensive, but more and more breeders find them a worthwhile investment. Likewise, some buyers may be willing to pay a bit more for tested animals. Genetic tests can also be seen as a lifetime investment — they don’t need to be replicated like disease testing does.
G6-Sulfatase testing has become more common in Nubian circles for both bucks and does. Labs can do it by collecting either blood or hair (with root bulbs attached) samples and sending them to an accredited lab. Does who have difficulty breeding can get a freemartin test also using either blood or hair.
With the rise of the scrapie eradication program, a susceptibility DNA test can indicate if a particular animal has a greater genetic resistance or susceptibility to scrapie. Note that this resistance is the result of a natural mutation occurring in goats, not necessarily because it’s engrained in a specific lineage.
Genetic tests are continually becoming more and more reliant on their information quantity and quality. But unfortunately, with limited research, the genetic tests available for goats aren’t quite as broad a spectrum compared to other livestock species. Nonetheless, these developments are worth keeping an eye on as more breeders increase their demands and more progress is made.
Understanding issues of genetic lines or breeds can help you avoid problems when selecting bucks for does. Testing and good recordkeeping can help avoid undesirable traits, but it certainly won’t guarantee anomalies will never arise. Remember, certain genetic defects can arise randomly from a shift or change in a gene without parental influence.
Line, S., & Dart, A. (2020, October). Congenital and inherited anomalies in animals – generalized conditions. Merck Veterinary Manual. Retrieved April 7, 2022, from https://www.merckvetmanual.com/generalized-conditions/congenital-and-inherited-anomalies/congenital-and-inherited-anomalies-in-animals
Veterinary Genetics Laboratory. (n.d.). G6-sulfatase deficiency (G6-S MPSIIID). G6-Sulfatase Deficiency (G6-S MPSIIID). Retrieved April 7, 2022, from https://vgl.ucdavis.edu/test/g6-s-goat#:~:text=G6%2DSulfatase%20deficiency%20is%20an,growth%20retardation%2C%20and%20early%20death
Vidinish, D. (2001). A Genetic Defect and its Management. Nubian genetic defect G-6-S (mucopolysaccharidosis IIID). Retrieved April 7, 2022, from http://kinne.net/g6s.htm
Originally published in the July/August 2022 issue of Goat Journal and regularly vetted for accuracy.