There has been a marked increase in recent weeks of queries relating to blindness in sheep and options for treating liver fluke in lambs destined for slaughter. Two reader queries are addressed here that capture relevant advice.
Q: “I have had an outbreak of blindness in one batch of finishing lambs over the last week. Lambs are not being fed silage or hay, which I know is often linked to issues, but are being fed meal in a creep feeder. There is a grey/blueish scum over their eyes and it is spreading pretty quick. Do I need to treat it or will it rectify itself?”
A. There was extensive coverage on eye issues at the Teagasc Hill Sheep Conference in 2022 by vet Gerard Roarty and Teagasc adviser Seamus Campbell.
There are two possible causes of the eye issue you describe: keratoconjunctivitis or ‘pink eye’, and Anterior Uveitis, which is commonly known as ‘silage eye’.
Both ailments are linked most commonly with the feeding of silage or hay and, particularly where sheep are burrowing their heads into forage or, in your case, eating in close confines at a meal trough.
Pink eye’s first early signs include tear stains in the area under the eye, a partially closed eye and, in more advanced cases, a reddening of the tissue around the eyeball (conjunctiva), which is normally a salmon colour.
The disease can progress quickly from conjunctivitis to ulceration and permanent loss of the eye, with temporary or permanent blindness.
The starting point with regard to treatment is to isolate any cases as soon as they are identified where practical, and to treat these accordingly. Moving animals to a sheltered paddock without the risk of falling into drains is generally best.
Treatment of the ailment is complicated by the fact that it is difficult to deliver the necessary concentration of medicine required to kill bacteria.
Moving animals to a sheltered paddock without the risk of falling into drains is generally best
Options include: intramuscular injection, subconjunctival injection, topical cream and ointment. Gloves should be worn where administering a subconjunctival injection or topical cream/ointment.
For ointment, the recommendation is to apply it at least three times daily, which is not readily practical in a lot of flocks.
Another limitation highlighted with this treatment route is that many licensed ointments contain cloxacillin, which is not active against mycoplasma species. A long-acting injectable oxytetracycline antibiotic may result in a clinical cure, but may not always eliminate the bacteria, meaning that the disease may reappear in these animals or they may become carriers.
There have also been queries received in the last week, questioning if ailments will resolve themselves over time.
Many animals will recover in time, but this approach is not an animal welfare-friendly approach and can lead to the disease progressing to active ulceration and corneal rupture and the loss of sight/eye.
Intervention must take place in such cases, along with the administration of pain relief.
The bacteria linked to silage eye, Listeria Monocytogenes – which is frequently found in poor-quality silage, badly preserved silage or mouldy silage – gives rise to its name.
Outbreaks typically occur 10 days after feeding poor-quality feed and cases of listeriosis can often also be seen.
Symptoms of silage eye are similar to pink eye, with regard to a watery discharge from eyes, a wet stained area under the eye and visible irritation.
There will also be a light blue, white or grey-coloured cloudiness or scum on the cornea of the eye, which leads to blindness in the eye. This sounds more like the issue you are experiencing in your flock.
Treatment options are also similar to pink eye and include topical antibiotics in ointment, aerosol or injectable form.
Gerard advised that a combination of 1cc of a steroid, such as dexamethasone, along with 1cc of oxytetracycline administered in to the sub-conjunctiva is more successful than antibiotics administered on their own.
Veterinary intervention is needed when working with steroids. This is due to the fact that products not licensed have to be used under cascade on welfare grounds, and also owing to the fact that steroids should generally not be administered to pregnant sheep.
Q. “I have lambs, which I estimate are about four to five weeks from slaughtering. A follow-up on the liver status of the last batch drafted showed active liver fluke infestation. What options have I to target at least immature stages of the parasites, as all products I have looked at have a long withdrawal period? The only ones with a short withdrawal period that I can see are those targeting adult liver fluke.”
A. You are right in your assessment that flukicides on the market that target early immature and immature stages of the liver fluke parasite have a longer withdrawal period, ranging from 42 days in closantel-based products to in excess of 60 days.
There are few alternative options where the target is to treat at least immature liver fluke.
Using a product which targets only the adult stage of liver fluke is not advised at present, as acute and sub-acute liver fluke is still the greatest threat.
This will typically remain the case until into the new year.
It is critical to highlight the importance of adhering to withdrawal periods and not drafting sheep that may have veterinary medicines in their system. Residues pose a risk to food safety and public health.
Withdrawal period must be considered also, for animals being drafted for sale live in marts or farm-to-farm.
Residues pose a risk to food safety and public health
It is the responsibility of the owners of animals to declare any recent veterinary medicines administered and the date of administration.
Producers should note that animals slaughtered are monitored on an ongoing basis for the presence of veterinary medicines.
Adhere to stated withdrawal periods on product packaging and use the correct dose for the weight of animals, as excessive volumes will increase the stated meat withdrawal period.