A new inherited ocular anomaly in pigmented white Leghorn chickens.

Abstract

Inherited ocular anomalies in chickens include several types of microphthalmia, retinal dysplasia, retinal degeneration, cataract, buphthalmos and pop-eye, or keratoconus in White Leghorns.2–5,7,8,12,15–18 In this report, a new ocular anomaly that appeared in pigmented White Leghorns homozygous for a mutation at the dominant white (I) locus is described with emphasis on clinical, gross, and histologic findings to aid in the diagnosis of the ocular lesions. An incompletely dominant mutation, called Smoky Joe (SJ), allows the production of feather pigment, which the I allele inhibits. The SJ mutation originally appeared in ADOL Line 0, a noninbred White Leghorn line maintained at the USDA Avian Disease and Oncology Laboratory (ADOL) in East Lansing, Michigan. Females homozygous for SJ have dark grey feathers with barring and homozygous males have much lighter colored plumage. This dimorphism in color is the result of the dilution that occurs with two copies of sexlinked barring in the males. The plumage of heterozygous birds (I, SJ) is intermediate in color compared to either parental type. Phthisis bulbi was noticed in adult females of the second generation of the homozygous SJ population. None of the parents of these females had apparent ocular lesions. Approximately 30% of the 85 surviving females had phthisis bulbi, while none of the 100 surviving males were affected. There was no clinical evidence of bacterial or viral infection, and the chickens were housed in pens isolated from chickens with experimental viral infections. Because the ocular anomaly appeared to be recessive and sex-linked, 4 test matings were designed to further study the inheritance. In matings 1 and 2, sighted SJ males, which were suspected of being carriers of the syndrome, were mated to either affected or sighted SJ females. These same male birds were then mated to either sighted females of Line 0 (II) (mating 3) or sighted females of ADOL Line 15I5 (II) and Line 0 (II) (mating 4). All chicks had ophthalmic examinations at hatch and 2, 4, and 8 weeks of age. In mating 1,197 chicks were examined. Of the females, 62% were affected, and 10% of the males were affected.