New Forest eye (NFE) is unfortunately a common disease of bovine eyes and can occur throughout the year, not just during the typical “fly season”. The disease NFE, also known as infectious bovine keratoconjunctivitis (IBK), is caused primarily by a Gram-negative aerobic bacteria, Moraxella bovis. The disease is a painful condition of the eye and is a significant welfare concern for affected animals. Despite this, the no doubt large economic impact of the treatment and the reduced performance (Funk et al., 2014) means a greater understanding of the disease, including prevention, would be welcomed by both farmers and vets.
Severe outbreaks of NFE in groups may be linked to underlying immune suppression, caused for example by a calf persistently infected (PI) with bovine viral diarrhoea (BVD) virus.
Clinical disease process
NFE presents in the early stages with tearing, blepharospasm and conjunctivitis, followed by stromal corneal ulcers and can end with a ruptured globe in the most severe cases (Figure 1). Surprisingly, even severely affected animals can recover with minimal corneal scarring, but blindness during the disease process creates a risk factor for further ocular damage from trauma.
Early identification is key and if lesions with ulcers or abscesses are seen, it could be useful to age the disease to help farmers understand how long the disease has been present. The corneal oedema severity and vascularisation of the lesion will indicate chronicity.
In the UK, the most common licensed topical treatment for NFE is a penicillin-based ointment and is used widely for early stages of the disease due to its ease of application and zero day withholds. Traditionally, many farmers have used antibiotic eye powders or intramammary tubes for the treatment of NFE. The latter is not appropriate and should be discouraged. Careful application of the ointment is essential and if only a single eye is visibly affected, it may be beneficial to treat the unaffected eye as well, ensuring to treat the healthy eye first to avoid cross contamination.
Eye injections or subconjunctival treatments are often a hot topic of debate. The first step is clarifying the location of the injection site and ensuring that the animal is receiving the correct treatment as opposed to an intramuscular injection in a highly sensitive area of the body (Figure 2).
Anecdotally, it is thought that subconjunctival injections on the scleral conjunctiva (bulbar or “white”) of the eye are more effective than at the palpebral location. Safe restraint of the animal is essential (Figure 3). Topical local anaesthetic should be applied to remove pain associated with the injection of an antibiotic bleb; 0.5% tetracaine drops although not licensed specifically for cattle have no maximum residue limits (MRL) required and so can safely be used under the prescribing cascade. The administration of antibiotics via subconjunctival route is off-licence, so again the treatment falls onto the prescribing cascade, resulting in a minimum of seven-day milk and 28-day meat withhold. Its use in lactating dairy cows is therefore not the best approach.
Steroid use in small animals is advised against in cases with corneal damage due to the delay in healing of the cornea (Belknap, 2015). However, in farm practice it is fairly commonplace to combine oxytetracycline with a short-acting dexamethasone for subconjunctival injections to provide immediate pain relief for the animal.
As with all lesions of the eye, they need treating promptly. Bulbar subconjunctival injections (Figure 4) have a role in treating NFE cases, but arguably should not be the first line of treatment. Rapid treatment with topical and/or systemic treatment is quick and stress free for the animal and prevents issues that can arise with some farms “saving up enough cows” to justify getting a vet out, the delay causing prolonged welfare issues and a likely poorer treatment outcome. The authors also feel it is unacceptable for anyone other than a vet to perform a subconjunctival injection due to the nature of the location and ability to provide topical local anaesthetic prior to injection. Inappropriate treatment used – be it location or medicine type, volume or combination – is likely to have adverse effects on healing and welfare.
Systemic treatment with an injectable antibiotic, such as oxytetracyclines or florfenicol, is effective at treating NFE (McConnel et al., 2007) is an easy and effective treatment but farmers may be put off by the cost when groups require treating (although speed and ease of administration probably negates this). Use of macrolides has been proven to be effective in treating NFE (Lane et al., 2006); however, the cost and responsible use of antibiotics makes this antibiotic class less appropriate.
Non-steroidal anti-inflammatory drugs
The authors would advocate the use of non-steroidal anti-inflammatory drugs (NSAIDs) in combination with antibiotic therapy for cases as it is deemed a painful condition (Hudson et al., 2008). However, there is limited evidence for the benefit of NSAID use in ophthalmic conditions in cattle.
For severe cases, surgical treatments in addition to one of the above methods may be necessary. Tarsorraphy, third eyelid flaps and in some cases enucleation may be necessary. The bovine eye appears to have remarkable powers of healing and it is not uncommon to have severely ulcerated eyes resolve with minimum scarring; enucleation should not be embarked on too quickly.
Metaphylaxis treatment for the whole group may be indicated on welfare grounds for groups with a significant proportion affected; the exact percentage to initiate metaphylaxis needs to be determined by the veterinary surgeon.
Management of disease
Animals severely affected by NFE bilaterally are often blind and as a result are easily panicked and wild in nature. It is important to ensure animals with reduced vision have easy access to food, remain in familiar surroundings, are kept with other animals and ideally where possible kept out of direct sunlight.
Prevention is key for the control and reduction of NFE, and it is important to note that younger animals are more prone to disease (Allan and Van Winden, 2020). Fly control, decreasing stocking density, improved ventilation and adequate feed and water space will help to minimise disease on-farm. For outdoor grazing animals, avoiding high-risk pastures where woodland is adjacent is useful. With regards to fly control, there are many options available including topical application of pyrethroids, fly tags, environmental control (surface spraying, parasitic larvae and reduction of fly breeding grounds) and above all ensuring animals are well grown, on a good plan of nutrition and have no underlying disease (eg BVD).