In a herd of Holstein Friesian cattle, (n = 98) kept in a loose housing system, we observed an outbreak of an unusual eye condition, which included unilateral or bilateral hyperaemic conjunctiva, lacrimation, photophobia, anterior uveitis, and cloudy cornea in four highly pregnant heifers, housed together with another older dry cow in dry cow group, during winter. The affected heifers were physically examined and conjunctival swabs, blood samples, individual raw milk samples of lactating cows (n = 78), and corn and hay silage samples were collected for laboratory analyses. Micrococcus sp. and Enterococcus faecalis were isolated from one conjunctival swab and Listeria monocytogenes from three others (three heifers). All the affected heifers were serologically negative in complement fixation test for listeriosis. Individual raw milk samples and grass and corn silage samples were negative for Listeria monocytogenes. Organoleptic and chemical analysis of wrapped baled grass silage showed that it was of inferior quality. The affected heifers were for 4 d systematically treated with oxytetracycline and ophthalmic ointment with hydrocortisone and oxytetracycline. All the heifers recovered within a fortnight. Ocular form of listeriosis in heifers was related to feeding of baled grass silage and traumatic injuries were caused by wind carrying particles of sawdust and mineral wool.
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