Veterinarian advises on how to protect eyes of beef cattle
“Even though we haven’t really seen a lot of resistance in face flies, it’s just good practice to be a little judicious,” she said. Severalpinkeyevaccinesexist,butMaier said it’s “difficult to make recommenda- tions, basedon theevidence thatwehave.” There are various risk factors, different bacteria and, within thosebacteria, differ- ent strains where one vaccine may work, and another doesn’t. “It just kind of depends on whether it covers the strain that is circulating in the herd,”Maier said. Timing of the vaccine is also important. “Has the vaccine been given at the right time, where the cattle had time todevelop immunity? And if it’s given too late, then wemay see outbreaks where a lot of cattle get it at the same time,”Maier said. Even with the vaccine, fly control re- mains important, she said. “I would still use fly control in addition to a vaccine, just because some years are worse for pinkeye,” Maier said. “Any vac- cine can be overwhelmed by large expo- sures, so if you had a lot of flies, you can be overwhelmed. I think amulti-pronged approach is always better.” There isminimal dataondeworming re- sistance inCalifornia,butbecausethereare onlya fewclassesofwormerandnothing in thepipeline,oncethesedrugsstopworking, there’snothingelse to fall backon, she said. Weighing animals and dosing to the weight is the ideal, but that may not be feasible. Instead, Maier advised ranchers
to consult with their veterinarians and to avoid underdosing. What animals should be treated?Maier recommends treating young, growing an- imals—calves that are close to weaning; stockers; replacement heifers; first-calf heifers; and bulls. “Youshoulddefinitelydewormbulls,be- causeyouonlyhavea fewof thoseandthey shouldbe in tip-top shape,”Maier said. Regardingyoungcalves, shesaid, “Some studies say yes, it helps. Some say no, it doesn’tmakeadifference. But I thinkclose to weaning, during that stressful period of weaning, maybe they get moved, that’s the time when deworming can be really beneficial for them.” These animals aremore vulnerable be- cause they haven’t built up immunity yet. Older cows, on the other hand, especially those that have been in the herd for a few years, that look good and have good body condition, probably don’t need to be de- wormed, she said. Pasturemanagement is also important. Maier saidmost of the infected larva reside in the bottom4 inches of the pasture, so if the pasture isn’t grazed too far down, the animalswillpickupfewer infectious larvae. Resting the pasture canhelp reduce the wormburden, too, shesaid,becauseby the time the animals return to thepasture, the worms will have died off. (Kathy Coatne y i s a repor t e r in Bend, Oregon. She may be contacted at kacoatney@gmail.com.)
ByKathyCoatney Pinkeye in beef cattle is a fairly com- mon disease and can be a frustrating to deal with, according to Gabriele Maier, extensionveterinarianat theUniversityof California, Davis. Pinkeye in cattle is a bacterial disease; Maier said the bacteriumMoraxella bovis is the cause that’s themost established. Face flies are considered a predispos- ing factor inpinkeye. They feedoneyeand nose secretions fromcattle, which is their source of protein. Face flies can do damage to the surface of the eye, Maier explained, and she said ultraviolet light also plays a role. “We know that cells in the cornea, the outermost layer of the eye, undergo an aging process, and you go from light cells tomediumtodark cells,”Maier said, add- ing Moraxella preferentially binds to the dark cells. UVlight contributes to theagingprocess of those cells, so if there’s a lot of UV light, there’s a lot of dark cells, making it easier forMoraxella to bind, Maier said. Another predisposing factor for pinkeye isgrasses. It’sthought thatwhencattlegraze, grasses canscratch the cornea, but she said nostudiesexisttoshowhowmucharancher couldreducepinkeyebymanagingpastures.
The main antibiotics for pinkeye are oxytetracycline and tulathromycin, but many others work, she said. Additional treatments such as Banamine—an an- ti-inflammatory—are frequently used, which she said makes the eyes less painful. Some producers use eye patch- es, alone or in combination with other treatments. A patch can shield the eye fromUV light and flies, Maier said. Vetericyn spray, an over-the-counter product, disinfects the eye, and a study found it to be beneficial, she said. “It’s supposedtokill thebacteria that are on the eyes, and in the study, it was used often: several times aday formultipledays in a row,”Maier said. Managing face flies is important. Insect growth regulators, or IGRs, represent one method for controlling face flies. IGRs are fed to cattle in mineral mixes or protein tubs, to interfere with development of the fly larva in feces. Ear tags arealsoused for fly control, and Maier said timing is important. “Don’t put themin toosoon, don’t leave them in too long,” she said. Maier recommends judicious use of fly control, especiallywith ear tags, and to fol- lowmanufacturerrecommendationsonthe lengthoftimetheeartagstaysontheanimal.
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April 28, 2021 Ag Alert 17
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