A novel day blindness in sheep: Epidemiological, behavioural, electrophysiological and histopathological studies Merav H. Shamir a,1 , Ron Ofri a,1 , Amir Bor b , Ori Brener c , Shay Reicher d,e , Alexey Obolensky f , Edward Averbukh f , Eyal Banin f , Elisha Gootwine e, * a Koret School of Veterinary Medicine, The Hebrew University of Jerusalem, Rehovot 76100, Israel b Bor Clinic, Tel Aviv 67329, Israel c The Weizmann Institute, Rehovot 76100, Israel d Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel e A.R.O., The Volcani Center, Bet Dagan 50250, Israel f Department of Ophthalmology, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel article info Article history: Accepted 20 May 2009 Available online xxxx Keywords: Awassi sheep Day blindness Achromatopsia abstract Four genetically related Improved Awassi sheep flocks had sporadic births of lambs with congenital visual impairments that differed from other known forms of sheep blindness. Pedigree analysis suggested an autosomal recessive mode of inheritance. Behavioural studies of 4-month old affected lambs showed that their day vision (but not night vision) was impaired. Electrophysiological results at this age demon- strated diminished function of cones but not rods. Histopathological and immunohistochemical evalua- tion of affected retinas from 5-month old lambs revealed both red-green and blue cones, suggesting that the behavioural day blindness and reduced cone electroretinograms reflect cone dysfunction rather than severe cone photoreceptor loss. Awassi day blindness may be a form of achromatopsia. Ó 2009 Elsevier Ltd. All rights reserved. Introduction Sporadic births of visually impaired Improved Awassi lambs have been noted since 2003 in the Ein Harod flock in Israel (B. Ope- mhiemer, personal communication). Similar reports have also emerged from three other flocks that over the last decade have established Improved Awassi breeding nuclei by purchasing rams and ewes from the Ein Harod flock. The affected lambs manifest impaired vision as early as 1 day of age. Despite their handicap, they grow to a marketing weight of about 50 kg, albeit at a slower growth rate compare to their normal counterparts. It has been pos- tulated that senses other than vision enable the lambs to orient themselves in the shed while searching for food and water. This condition differs from other cases of sheep blindness so far reported. Intoxication (Borges et al., 1999), nutritional imbalance (O’Toole et al., 1996) and infectious diseases (Christodoulopoulos et al., 2008) can cause blindness in sheep, but these diseases usu- ally manifest in adulthood and are characterised by blindness that is followed by neurological abnormalities not observed in the Awassi lambs (Abo-Shehada et al., 2002). The impaired vision of Awassi sheep also differs from ‘bright blindness’ caused by pro- gressive degeneration of the retina due to consumption of bracken fern (Pteridium spp.) (Watson et al., 1972), from blindness caused by inherited ceroid lipofuscinosis (Shelton et al., 1993) and from blindness associated with microphthalmia, a recessive genetic dis- order in Texel sheep (Tetens et al., 2007). The Ein Harod dairy flock has been a closed flock for several dec- ades. Foreign genetic material was introduced only once (in 1986) following insemination of Improved Awassi ewes with semen ta- ken from five Booroola Merino rams (Gootwine et al., 2008). The recent observation of impaired vision in four genetically connected flocks run under different husbandry conditions suggests that the Awassi blindness has a genetic rather than environmental back- ground and is due to a relatively recent genetic event. The aim of this study was to investigate the clinical, behavioural, electrophys- iological and structural characteristics of this novel disease of im- paired vision in sheep and to establish its mode of inheritance. Materials and methods Animals The intensive management of the Improved Awassi dairy flock of Ein Harod is described elsewhere (Gootwine and Pollott, 2000). The flock is kept indoors year round and reproductive management includes controlled breeding of ewes follow- ing heat detection. At 1 day of age, all lambs are tagged, their birth weight is re- corded and they are moved to an artificial rearing unit until weaning at about 35 days of age. After weaning and during the fattening period, ram lambs and 1090-0233/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2009.05.029 * Corresponding author. Tel.: +972 3 9683752; fax: +972 3 9603678. E-mail address: gootwine@agri.gov.il (E. Gootwine). 1 Both authors contributed equally. The Veterinary Journal xxx (2009) xxx–xxx Contents lists available at ScienceDirect The Veterinary Journal journal homepage: www.elsevier.com/locate/tvjl ARTICLE IN PRESS Please cite this article in press as: Shamir, M.H., et al. A novel day blindness in sheep: Epidemiological, behavioural, electrophysiological and histopathol- ogical studies. The Veterinary Journal (2009), doi:10.1016/j.tvjl.2009.05.029