Kerala, India
Fortunately, sheep possess relatively few inherited defects that compromise their survival or production capacity. A discussion of the primary genetic defects follows.
Jaw defects. Jaw defects occur in virtually all sheep breeds and are associated with improper alignment of incisor teeth to the dental pad. An undershot jaw occurs when incisor teeth extend forward beyond the dental pad; an overshot jaw occurs when teeth contact behind the dental pad (this condition is termed parrot mouth). Cull sheep displaying either genetic defect. If the sire and dam can be identified, eliminate them from the flock.
Rectal prolapse. Rectal prolapse represents a serious defect most commonly observed in meat-type sheep. It occurs most frequently among lambs receiving high-concentrate rations. This weakness is believed to result from inheritance. Surgical correction is sometimes attempted for this condition, but affected animals frequently prolapse again after surgery. Cull breeding sheep exhibiting this condition from the flock.
Inverted eyelids. Inverted eyelid (entropion) is prevalent among most sheep breeds. This trait demonstrates high heritability. Inverted eyelids involve an inward “rolling” of the eyelid margin. This condition produces severe irritation and, if unaddressed, can ultimately cause blindness. The condition may be observed at birth and treated immediately. One treatment method involves clipping a metal suture to the affected eyelid center. Gather sufficient skin under the clip in a vertical direction to hold the lid away from the eye. The clip can remain in position for several days. Mark affected lambs and prevent them from entering the breeding flock.
Cryptorchidism. Rams with one or both testicles retained in the abdomen are cryptorchids. The condition typically inherits as a simple recessive trait. Some association appears to exist between this condition and the polled characteristic found in some fine-wool rams. Purebred breeders should make comprehensive efforts to eliminate this condition.
Skin folds. Skin folds are highly heritable. They were once deemed desirable in some fine-wool breeds because they provide additional surface area for wool growth. This condition is no longer considered advantageous, and most purebred breeders are attempting to breed smooth-bodied sheep. Excessive skin folds are positively associated with reduced fertility and overall productivity. Additionally, folds are difficult to shear and are susceptible to insect attack.
Face covering. The quantity of wool growing on the face is also highly heritable. Cull sheep with excessive wool growing below the eyes and on the lower facial areas because face wool can obstruct vision. Ewes with impaired vision are generally less productive than open-faced ewes.
Fleece defects. Some inherited fleece defects include the occurrence of belly-type wool growing high on the sheep’s side, hairiness or hairy wool, and colored wool. Through a rigorous selection and culling system, the potential for genetic defects can be minimized.
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