Ulna: One of the two bones of the forearm.

Umbilical Hernia: A usually self-correcting hernia of the intestines in which protrusion occurs through the abdominal wall in the region of the navel.

Underage Dam: Dam under eight months of age at the time of mating.

Underage Sire: Sire under seven months of age at the time of mating.

Undercoat: Dense, soft, short coat concealed by a longer top coat.

Underline: The combined contours of the brisket and the abdominal floor.

Undershot: The front teeth (incisors) of the lower jaw overlapping or projecting beyond the front teeth of the upper jaw when the mouth is closed.

Unilateral Cryptorchid: See Cryptorchid

United Kennel Club (UKC): An official registry in the United States for purebred dogs.

Unsound: A dog incapable of performing the functions for which it was bred.

Upper Arm: The humerus or bone of the foreleg, between the shoulder blade and the forearm and associated tissues.

Urethroliths: A general term referring to mineral deposits that form an obstruction in the urethra of male dogs.

Uterus: A hollow muscular organ located in the pelvic cavity of female mammals in which the fertilized egg implants and develops. Also called womb.

Utility Dog (UD): A title awarded to a dog that has been recorded a Utility Dog by the AKC as a result of having won certain minimum scores in Utility classes at a specified number of AKC licensed or member obedience trials. This title may be combined with the TD or TDX title and shown as UDT or UDTX, respectively.