Jaw Defects in Sheep

Prognathism and Brachygnathism


Jaw defects in sheep, Prognathism and Brachygnathism, or "bulldog mouth" and "parrot mouth", appear occasionally as genetic abnormalities in most breeds of sheep, but it is especially common in some of the meat-type breeds such as Suffolk, Hampshire, etc.

Between the two, bull-dog jaw seems to be the more common type, and it is more of a handicap to sheep than parrot-mouth is.

What is it?

  • Jaw defects are associated with the failure of the incisor teeth to properly meet the dental pad.
  • Overbite: "Parrot Mouth" (Branchygnathia)- This condition is when the upper jaw is longer than the lower jaw, and there is a gap between the upper and lower incisors when the mouth is closed
  • Underbite: " Bulldog or Monkey mouth" (Prognathism)- This condition is when the lower jaw is longer than the upper jaw.
  • If lamb is identified with a jaw defect, it will not be able to properly nurse, which will result in not getting enough nutrition, or eat from a creep feeder.
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Genetic Transmission

  • Jaw defects are inherited traits, also known as autosomal recessive traits, and it is when there is a failure of the incisor teeth to properly meet the dental pad.
  • These defects are known as recessive characters, which means that both rams and ewes may have normal mouths and throw offspring with the defects.


The most effective way to reduce the number of sheep affected with jaw defects is to identify the sire and dam of the offspring, and cull accordingly.

When breeding, breeders should only use rams and ewes that are free from Prognathism and Brachygnathism, as well as making sure their line of ancestors is free from the defects.

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To prevent jaw defects in sheep, breeders of sheep should be able to recognize these defects and cull the sire and dam of the offspring, and make sure that all other animals in their flock do not show signs of these defects.

Discussion Point


Is it ethical to cull animals who show signs of jaw defects, regardless of the impacts it can have on them? Are there other ways to prevent your flock from getting this type of defect, even though the traits are inherited from their parents?



  1. http://www2.luresext.edu/photos/undershot.jpg
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  • McNeal, Lyle G. "Bulldog Jaw and Parrot Mouth Defects in Sheep." (n.d.): n. pag. Web. 29 Apr. 2016.