Pink eye hits fast. One morning you’re checking bunks, and everything looks fine. Two days later you’ve got a steer squinting, tearing up, and standing off from the group with one eye clamped shut. Left alone, that eye can ulcerate, cloud over, and rupture inside a week.
The fix in a pasture setting is oxytetracycline (LA-200 or an equivalent), 4.5 ml per 100 pounds of body weight, given subcutaneously in the neck, then repeated 48 to 72 hours later. Slap a glue-on eye patch over the affected eye to block sunlight and flies, and tighten fly control across the whole herd before you have twenty more head with the same problem.
That’s the short version. The rest of this article covers what to do when standard treatment isn’t holding, why pink eye keeps coming back in the same pastures every summer, what actually happens when you try WD40 or ivermectin, and the fescue-endophyte connection almost nobody talks about.
What causes pink eye in cattle?
Pinkeye in Cattle: Visual Examples
These images show how pinkeye can progress from early tearing and irritation to more advanced clouding and discharge.
Pink eye in cattle is infectious bovine keratoconjunctivitis, or IBK. The main culprit used to be Moraxella bovis. It still is in a lot of cases. Over the last fifteen years, though, Moraxella bovoculi has been showing up more often and doesn’t always respond to the same treatments. Some outbreaks also involve Mycoplasma bovoculi and IBR virus, which can muddy the picture and change what works.
The bacteria live in tears and nasal secretions of infected cattle. They spread through direct nose-to-nose contact and through face flies that feed on eye secretions and move from animal to animal. Anything else that touches multiple eyes can carry them too, whether that’s a scratchy piece of hay or a rough post at the mineral station.
UV damage, dust, tall seed heads, and face flies tip the balance from carrier to case. A healthy eye can handle a low bacterial load all day long. Scratch the cornea with a foxtail seed head, expose it to a hot sun with a face fly walking across it, and you’ve got pink eye by Thursday.
What are the first signs of pink eye in cattle?
The symptoms of pink eye in cattle progress through four stages. Catching it at stage one saves the eye and saves you money on drugs.
Early tearing and squinting
Excessive tearing and squinting, sometimes with a slightly reddened conjunctiva. The eye still looks clear. Treated at this point, most cases clear in 5 to 7 days with a single round of antibiotics.
White spot on the cornea
A white spot appears in the middle of the cornea. That’s the ulcer starting. The eye is cloudy around it, and there’s real pain. The animal will hold the eye shut most of the day. Still treatable, but the eye may carry a scar.
Deep ulceration and cloudiness
Deep ulceration with pronounced cloudiness across most of the cornea. You may see a yellowish tinge and the eye can bulge from swelling behind it. Treatment gets harder. Permanent vision damage in that eye is likely even if you save it.
Rupture
The cornea perforates, aqueous humor leaks, and the eye collapses. Nothing saves the eye at that point. You can save the animal from further infection, but the eye is gone.
If you’ve never seen the stages up close, pull up pictures of pink eye in cattle before season starts and study them alongside photos of foot rot in the face, cancer eye, and IBR. They can look similar in early stages, and misdiagnosis wastes drugs and time.
Check eyes every time you’re in the pasture from May through September. A squinting animal a hundred yards off isn’t hard to spot once you’re looking for it.
How do you treat pink eye in cattle?
The best antibiotic for pinkeye in cattle in a commercial cow-calf setting is oxytetracycline, sold as LA-200, Bio-Mycin 200, or generic equivalents. For stubborn cases and heavy stage three ulcers, tulathromycin (Draxxin) is the second-choice drug. Both work systemically. Subconjunctival injection and eye patches are the tools that turn a slow-healing case into a fast-healing one.
Oxytetracycline (LA-200 and equivalents)
Dose is 4.5 ml per 100 pounds of body weight, given subcutaneously in the neck.
A 1,200-pound cow gets about 54 ml. That has to be split across multiple sites. Beef Quality Assurance guidelines cap subcutaneous doses at 10 ml per site, so a mature cow’s dose goes into five or six locations along the neck. For a 500-pound calf, the dose works out to about 22 ml split into three sites.
The second dose goes in 48 to 72 hours after the first. In my experience, 72 hours is enough for stage one and early stage two cases. Stage three cases usually need a third dose around day 5 or 6.
Slaughter withdrawal on LA-200 is 28 days for beef cattle. Not something most cow-calf operators think about with a mature cow, but it matters if you’ve got a bull you’re culling or a fed steer close to finish. Since the 2023 FDA prescription rule change, you’ll also need a script from your vet before you can buy it.
Cost per head runs about $4 to $8 depending on where you buy and what animal size you’re dosing.
Tulathromycin (Draxxin, Increxxa, generics)
Heavier hitter. Dose is 1.1 ml per 100 pounds, given subcutaneously in the neck, single dose. Cost per head is roughly $20 to $40 depending on animal size and where you source it.
I go to tulathromycin when I’ve got a stage three case, a bull I can’t safely run through the chute twice in a week, or when LA-200 stops holding on a specific pasture. Some Moraxella bovoculi strains are showing resistance to tetracyclines but still respond to macrolides.
Slaughter withdrawal is 18 days.
Subconjunctival injection
This is where a lot of ranchers stop reading. It sounds intimidating. It’s actually the best tool for a stubborn stage two or stage three case, and it isn’t hard to learn. Have your vet show you the first time.
You inject 1 ml of procaine penicillin G (300,000 IU/ml) or 1 ml of tulathromycin under the bulbar conjunctiva, which is the membrane covering the white of the eye. Use a 20-gauge, one-inch needle. The needle goes under the mucous membrane sitting on top of the eye. It doesn’t enter the eye itself. The tissue bubbles up like a small blister when you inject. That’s what you want.
The advantage is putting the drug right where the infection is at a concentration you couldn’t get systemically. A subconjunctival injection can turn a stage three case around in 24 hours when systemic antibiotics are still working their way in.
The downsides are that it requires a good chute, a headlock or halter that keeps the head steady, and confidence. If you’ve never done it, don’t learn on your best cow.
Eye patches
Patches don’t cure pink eye. They protect the eye from sunlight and flies while the antibiotics work. On a stage two case or worse, a patch cuts recovery time roughly in half.
The glue-on patches from Nasco, Valley Vet, or the co-op work fine. Clip the hair around the eye with a #10 blade, apply a thin bead of the included adhesive around the eye socket (never on the eye itself), press the patch on firmly, and hold for thirty seconds. The patch stays on for 10 to 14 days and falls off naturally.
Common patch mistakes include gluing the patch to the eyelashes so it pulls the lid open, using too much adhesive so it runs into the eye, and patching an eye with active pus discharge. If there’s active discharge, treat systemically for 48 hours first, then patch.
How long does it take for pink eye to go away in cattle?
Timeline depends on the stage you catch it and whether you actually treat.
Stage 1, treated at first sign: eye clears in 5 to 7 days. Squinting stops within 48 hours of the first antibiotic dose.
Stage 2, treated within 24 hours: 10 to 14 days for the ulcer to close. A small permanent scar on the cornea is likely but vision usually stays intact.
Stage 3, treated aggressively with subconjunctival injection and patch: 3 to 4 weeks. Vision loss in the affected eye is probable even with treatment.
Untreated cases: unpredictable. Some clear on their own within 2 to 3 weeks if fly pressure drops and the animal has good immune function. Most progress. Field estimates suggest 30 to 50 percent of untreated moderate cases end up with lasting vision damage.
The animal stays infectious to herdmates through face flies for the whole clinical course and for weeks after visible signs resolve. That’s why fly control matters as much as antibiotic treatment.
Treatment mistakes that cost you the eye
Underdosing. LA-200 gets estimated at “about 40 ml” for a cow that actually weighs 1,300 pounds. A short dose means a partial kill on the bacteria and a higher chance of resistance developing in that population. Use a weight tape if you don’t have scales.
Skipping the second dose. LA-200 is called “long-acting” but it isn’t a single-shot treatment for pink eye. Bacteria that survive the first dose will rebound if you don’t hit them again within 72 hours.
Treating without a patch. On a hot, sunny July day with face flies at 40 per animal, systemic antibiotics can’t keep up with the reinfection rate. Patch the eye or accept slower recovery.
Waiting too long. Every day you delay treatment, the ulcer gets deeper. A stage one case treated on day one costs about $6 in drugs and clears in a week. That same case at stage three costs $28 in drugs plus a subconjunctival injection plus a patch, and leaves a permanent scar on the cornea.
Do WD40, ivermectin, or home remedies actually work?
Every summer someone at the sale barn swears by WD40, or ivermectin poured in the eye, or a colloidal silver flush. The reality on each is different.
WD40 for pink eye in cattle. It doesn’t work. There’s a persistent story that spraying WD40 in the eye clears pink eye. What actually happens is that WD40 coats the eye briefly and possibly reduces fly attraction for a few hours. It doesn’t kill Moraxella. Putting a petroleum-based lubricant on an ulcerated cornea can cause chemical irritation that slows healing. Skip it.
Ivermectin. Ivermectin is a parasiticide. It does not affect bacteria. Pour-on ivermectin knocks down face fly populations for a few weeks after application, which reduces disease spread across the herd, so it can help indirectly as a prevention tool. Ivermectin poured directly into the eye doesn’t treat pink eye and can irritate.
Natural treatment for pink eye in cattle. The most common home remedies are saline flushes, honey, colloidal silver, and raw apple cider vinegar. Saline flushes actually do help by clearing debris and secretions from a scratched cornea, and are worth doing before a systemic treatment goes in. Honey has mild antibacterial properties but isn’t strong enough to clear an established Moraxella infection. Colloidal silver has never demonstrated meaningful bacterial kill on Moraxella in peer-reviewed testing. Apple cider vinegar in an already-inflamed eye burns and slows healing.
If you can’t use antibiotics for organic-certification reasons, your only real tool is aggressive prevention: face fly control, mineral, pasture management, and immediate isolation of affected animals. Certified organic operators should call their vet and their certifier before an outbreak, not during one.
Why pinkeye keeps coming back in the same pastures
If pink eye has broken out in the same paddocks three summers running, luck isn’t the issue. Four factors are usually at play, and you can influence all of them.
Face flies
The face fly (Musca autumnalis) is the primary mechanical vector for pink eye. They feed on eye and nasal secretions and move from animal to animal. Twenty face flies per animal is the threshold where pink eye risk climbs sharply. Above 50, you’ll almost certainly see cases.
Fly control that actually works is layered. Insecticide ear tags (two per animal, rotated between chemical classes each year to prevent resistance) give you 12 to 15 weeks of coverage. Dust bags at mineral feeders and water points extend that. Pour-ons every three to four weeks bridge gaps in coverage.
Feed-through IGRs (insect growth regulators) like Altosid in mineral break the fly life cycle in manure. They don’t kill adult flies. They stop larvae from developing into new adults. Combined with tags and dust bags, feed-through IGR can drop face fly counts 60 to 80 percent by mid-summer.
Tall grass and seed heads
Foxtail, mature brome, and Johnsongrass seed heads scratch corneas as cattle graze. A scratched cornea is where Moraxella gets its foothold. Rotational grazing that keeps swards under 12 inches during peak pink eye season reduces mechanical eye trauma noticeably.
UV exposure and face pigmentation
White-faced cattle (Herefords, some Simmentals, Hereford-cross cows) get pink eye at higher rates than dark-faced cattle. Less pigment around the eye means less UV protection for the cornea. You can’t change the herd you have this summer. If you’re buying replacements, factor eye pigmentation into your selection.
Mineral status
Copper and selenium deficiencies suppress immune function. Cattle on a short mineral get pink eye more often and take longer to clear. Pull the tag on your mineral and compare copper (should be 1,500 to 2,500 ppm for most regions) and selenium (26 to 40 ppm depending on your state’s FDA maximum).
The fescue connection almost nobody talks about
Endophyte-infected tall fescue produces ergot alkaloids that constrict blood vessels. Cattle grazing hot fescue in summer have reduced blood flow to the extremities and to the eye, which impairs immune response and slows healing.
If you’re on Kentucky 31 or unimproved fescue and you’re seeing more pink eye than your neighbor across the fence line, look at the fescue first. Interseeding red clover dilutes the endophyte load. Rotating to a Bermuda paddock or a novel-endophyte fescue variety during peak summer works even better.
I’ve watched a herd on hot fescue go from a 25 percent pink eye rate to under 5 percent in two years by interseeding red clover and moving the cows to a Bermuda paddock from mid-June through August. Same fly load, same UV, same everything else.
When should you call the vet for pink eye?
Pick up the phone if any of the following is true:
- You’ve treated with two doses of LA-200 and the eye is worse at day 5
- The cornea has ruptured or looks like it’s about to
- More than 20 percent of the herd is affected within a week
- A calf under 200 pounds is affected (dosing gets tricky and small calves go bad fast)
- You’re dealing with a bull you can’t safely handle in your chute for a second dose
A farm call for a bad pink eye case runs $80 to $150 in most parts of the country. Compared to losing an eye on a $2,200 bred heifer, that’s a bargain.
How do you prevent pink eye in cattle?
Print this and put it on the wall of your working facility.
April, before pink eye season:
- Insecticide ear tags at spring processing, two per animal, rotated class from last year
- Start feeding IGR mineral by mid-April
- Clip pastures that carried foxtail or brome seed heads last summer
- Verify mineral copper and selenium levels
May through September, during the season:
- Check eyes every pasture drive-through
- Refresh dust bags monthly at mineral and water points
- Rotate pour-on applications every three to four weeks
- Keep grazing swards under 12 inches where you can
- Treat any suspected case at stage one the same day you spot it
October, after the season:
- Pull spent ear tags to prevent resistance building in overwintering fly populations
- Note which pastures had the worst outbreak and plan clipping for next spring
- Restock patches, LA-200, syringes, and needles before winter
FAQs
What’s the fastest treatment for pinkeye in cattle?
A single dose of tulathromycin (Draxxin) at 1.1 ml per 100 pounds subcutaneously, paired with a glue-on eye patch, is the fastest field treatment for a moderate case. Most animals show clear improvement within 24 to 48 hours.
Can pinkeye go away on its own without treatment?
Mild stage one cases sometimes resolve if the animal is otherwise healthy and fly pressure is low. Waiting is a bad bet in July or August. Untreated stage two cases usually progress to ulceration and permanent scarring.
How long is a cow contagious with pinkeye?
Cattle can shed Moraxella for weeks to months after clinical signs resolve. Some animals become long-term carriers. That’s why fly control matters even after visible cases have cleared.
What’s the LA-200 dose for pinkeye in a 500-pound calf?
About 22 ml, subcutaneously in the neck, split across two or three sites, repeated in 48 to 72 hours. Give it in the neck rather than the hip because injection-site lesions in the round hurt carcass value later.
Does the pinkeye vaccine work?
Commercial killed vaccines like Piliguard and Alpha-7/MB-1 can reduce clinical severity but rarely prevent pinkeye outright. Autogenous vaccines made from your own herd’s Moraxella strains work better but cost more and require lab turnaround time. Fly control gives you more bang for the buck than vaccination in most operations.
Do face flies bite cattle?
Face flies don’t bite, they sponge. They feed on tears, saliva, and other secretions. That sponging action is exactly what spreads Moraxella from one animal’s infected eye to the next animal’s healthy eye.
The bottom line
Pink eye is one of the most common summer problems in beef herds and one of the most preventable. The treatment itself isn’t complicated. What separates ranchers who spend a full day a week treating pink eye cases from ranchers who see two or three cases a summer is the prevention work done in April and the willingness to treat at stage one instead of waiting until it’s ugly.
Keep patches, LA-200, and syringes stocked from May through September. Check eyes every time you’re horseback or on the four-wheeler. If you keep seeing the same problem in the same pasture year after year, the fix probably isn’t more antibiotics.
This article is for educational purposes and reflects practices used in commercial cow-calf operations. Work with your veterinarian on treatment protocols, especially when a case isn’t responding or when using antibiotics that require a Veterinary Feed Directive or prescription in your state.