Monitoring and management of congenital entropion in lambs: A prospective study

Comparison of entropion outcome with and without intervention in Romane and Ile de France sheep breeds

BACKGROUND

Congenital entropion is the most frequent ocular disorder in newborn lambs of certain sheep breeds, which, if not treated, can result in complete blindness and death due to starvation.

OBJECTIVES

The aims of this study were to compare the spontaneous healing of entropion in two breeds and assess the outcome of cases with and without therapeutic intervention.

METHODS

A total of 158 entropion cases (119 Ile de France and 39 Romane) were investigated, and swab samples were collected from the cornea and conjunctiva of 73 of the affected lambs for bacteriological investigation. In addition, an ocular intervention was carried out in 123 affected animals.

RESULTS

The Romane breed developed entropion at an average age of 7 days compared to the Ile de France, which developed it at an average age of 1 day. Likewise, significant differences were found between bilateral and unilateral involvement in both breeds. Meanwhile, 22.1% of cases recovered spontaneously, and the highest rate of spontaneous recovery without intervention was observed in the Romane breed (66%). Bacteria isolated from ocular samples included Staphylococcus spp. (42.5%), Bacillus spp. (21.9%), Trueperella pyogenes (13.7%), Corynebacterium spp. (12.3%) and Escherichia coli (9.6%).

CONCLUSIONS

The results of the study showed that the onset time of entropion, bilateral involvement, the severity of the process and the need for re-treatment were higher in the Ile de France breed than in the Romane breed. Likewise, the Romane breed showed a higher degree of spontaneous recovery of entropion.

Genome-Wide Association Identifies SLC2A9 and NLN Gene Regions as Associated with Entropion in Domestic Sheep

Entropion is an inward rolling of the eyelid allowing contact between the eyelashes and cornea that may lead to blindness if not corrected. Although many mammalian species, including humans and dogs, are afflicted by congenital entropion, no specific genes or gene regions related to development of entropion have been reported in any mammalian species to date. Entropion in domestic sheep is known to have a genetic component therefore, we used domestic sheep as a model system to identify genomic regions containing genes associated with entropion. A genome-wide association was conducted with congenital entropion in 998 Columbia, Polypay, and Rambouillet sheep genotyped with 50,000 SNP markers. Prevalence of entropion was 6.01%, with all breeds represented. Logistic regression was performed in PLINK with additive allelic, recessive, dominant, and genotypic inheritance models. Two genome-wide significant (empirical P<0.05) SNP were identified, specifically markers in SLC2A9 (empirical P = 0.007; genotypic model) and near NLN (empirical P = 0.026; dominance model). Six additional genome-wide suggestive SNP (nominal P<1x10^-5) were identified including markers in or near PIK3CB (P = 2.22x10^-6; additive model), KCNB1 (P = 2.93x10^-6; dominance model), ZC3H12C (P = 3.25x10^-6; genotypic model), JPH1 (P = 4.68x20^-6; genotypic model), and MYO3B (P = 5.74x10^-6; recessive model). This is the first report of specific gene regions associated with congenital entropion in any mammalian species, to our knowledge. Further, none of these genes have previously been associated with any eyelid traits. These results represent the first genome-wide analysis of gene regions associated with entropion and provide target regions for the development of sheep genetic markers for marker-assisted selection.