Summer months in the northern plains mean an opportunity for cattle producers to graze weaned calves on pasture. While “grass calves” are considered to be under less risk of infectious diseases compared to calves weaned and concentrated into drylots in the fall, these calves still are at risk for certain disease issues while out on pasture. What are the major illness risks for weaned calves on pasture, and what can be done for prevention? Pasture diseases for which vaccination may play a role include:
- Blackleg. This disease is caused by toxins that are released from the bacterium Clostridium chauvoei. Spores (environmentally-resistant forms) of this germ are fairly common in the soil where animals have grazed. Certain pastures seem to be more at risk than others. Blackleg hits calves so quickly that it’s uncommon to see signs of illness, such as acute lameness. More often than not, previously healthy calves are simply found dead on pasture.
It’s a widely held view by most veterinarians that one dose of a bacterin-toxoid against blackleg (normally contained in “7-way” Clostridial vaccines) is protective through the grazing season. Calves that have not previously received 7-way vaccines should get a dose prior to turnout. It’s unclear whether one dose of “7-way” given to a newborn fall calf is enough to protect against blackleg the subsequent summer; it’s probably best that those calves receive a booster going out to pasture as well.
- Pinkeye. A common scourge among calves on summer pasture, pinkeye has proven to be a challenging condition when it comes to prevention through vaccination. Many commercial vaccines are available against Moraxella bovis, the most common species implicated in pinkeye cases. Autogenous (farm-specific) vaccines are becoming widely used in individual herds where other strains such as M. ovis or M. bovoculi have been found.
However, vaccination has not been found to universally prevent pinkeye. It’s been considered by most veterinarians that successful prevention through vaccination may occur when vaccine strains match the outbreak strains. Therefore, vaccines that contain many different strains of bacteria may be better choices than single-strain vaccines. As with many conditions, pinkeye is a multifactorial illness: eye irritation due to flies, dust, and tall grass can create the right conditions for the bacteria to take hold. Attention to these other factors can greatly enhance the success of a prevention program.
- Respiratory disease. Weaned calves on grass are usually considered at a lower risk for bovine respiratory disease complex than calves weaned into a backgrounding lot, however, conditions sometimes exist that can make respiratory disease pop up on summer pasture. Calves that have been properly pre-conditioned with respiratory vaccines administered prior to weaning are likely well-protected against illness due to viruses such as IBR, BVD, and BRSV. Fall calves that have not received these vaccines (4-way virals and possibly Mannheimia hemolytica) should get at least one dose (depending on the particular product) prior to pasture turnout.
- Anthrax. Certain locations in the Dakotas are especially prone to problems with anthrax. This disease shares a few features with blackleg, discussed above. In particular, the bacteria (Bacillus anthracis) produces a toxin that usually acts so quickly that cattle are found dead with no prior clinical signs. And like blackleg, the bacteria forms spores that are extremely resistant to destruction due to environmental conditions. Conditions present this summer, especially in areas adjacent to where the Missouri River flooded last year, have the potential to produce conditions in which anthrax spores may be more readily available to cattle grazing those areas.
Animals going out to pasture in anthrax-endemic areas should be vaccinated with anthrax vaccine upon turnout. One dose of this vaccine is considered to provide protection through the grazing season. Anthrax is a reportable disease with human health implications, and a key reason why pastures should be checked frequently during the summer and death losses promptly investigated.
Successfully getting calves through the summer grazing months depends on many factors, only one of which is the proper vaccination program. These factors are different for every group of calves and every pasture, so having a conversation with a local expert—your veterinarian—is a great first step in ensuring a successful grazing season.