I recently attended the Ohio Beef Cow/Calf workshop held in Washington County, where the focus was reproduction and genetics as important factors that ensure longevity within a herd.
As the crowd learned about profitability and genetic selection using expected progeny differences and forage testing, questions arose around disease prevention and control. The two diseases that were brought up were blackleg and grass tetany.
While I don’t get many questions on blackleg, I do get multiple questions each spring about grass tetany and how to prevent it. These are two issues that are highly preventable through proper vaccination protocols and management.
Let’s take a closer look at how each of these illnesses present themselves in cattle and how we can prevent them.
Grass tetany
Grass tetany is a metabolic disorder caused by dangerously low magnesium levels in grazing cattle, most often in early spring when lush, rapidly growing grasses dominate pastures. It progresses quickly and can be fatal, which is why understanding its causes, symptoms and prevention is essential for anyone managing cattle.
Grass tetany is a form of hypomagnesemia, meaning magnesium levels in the blood and cerebrospinal fluid drop below what the nervous system needs to function normally.
It most commonly affects lactating cows, whose magnesium demand is highest, animals that are grazing lush, cool-season grasses and cattle that are exposed to rapid spring pasture growth. Magnesium deficiency develops because young grasses often contain low magnesium, high potassium and high nitrogen, a combination that interferes with magnesium absorption in the rumen.
So, why does this happen? There are several environmental and nutritional factors taking place at this time that create the risk of grass tetany.
• Lush spring growth dilutes magnesium in plant tissue.
• High potassium and nitrogen in young grass block magnesium uptake.
• Low soil magnesium, especially in fields limed with calcitic rather than dolomitic lime because it can reduce the mineral available to plants.
• Cold, cloudy weather slows grass growth and further reduces magnesium content.
• High milk production increases magnesium demand in cows.
These factors make early spring the most dangerous period, especially for high-producing cows turned out onto fresh pasture.
Symptoms start out subtly and, within hours, can escalate and become dangerous if not observed. Symptoms alerting you to this condition include: twitching, hypersensitivity, uncoordinated gait, muscle spasms, rapid breathing, collapse or seizures. Because progression is rapid, any suspicion of grass tetany is an emergency requiring immediate veterinary attention. Treatment requires precise dosing and monitoring, so it must be performed by a veterinarian or under veterinary guidance.
Prevention. We all know prevention is easier than treatment and in most cases much less expensive. From a management standpoint, what are some preventative measures that can be taken?
First, we can use magnesium supplementation and include a free-choice mineral mix that contains magnesium.
Second, we can be more selective about who is going into the pastures. Keeping older, high-producing cows off high-risk pastures during that early spring flush and providing hay before turnout to reduce rapid intake of lush grass can help protect cattle from grass tetany.
Third, we can be more proactive in our pasture management by avoiding turning high-risk cattle out into lush spring pasture without supplementation, mixing grasses with legumes, which tend to have higher magnesium and managing our soil fertility to avoid excessive potassium and nitrogen.
Blackleg
Now that I have mentioned soil fertility, let’s talk a little about blackleg. Blackleg is a rapidly fatal clostridial disease of cattle caused by Clostridium chauvoei, a soil-borne bacterium that can persist for years and strike without warning.
It is considered one of the most devastating diseases in beef production because it often kills the healthiest animals in the herd. Blackleg is an acute, highly fatal infection that affects cattle — most commonly those between 6 and 24 months old — and occasionally sheep. The bacteria enter the body when animals ingest spores from contaminated soil.
These spores can remain dormant in muscle tissue until activated by bruising, rapid growth or other stressors. Once activated, the bacteria multiply quickly and release toxins that destroy muscle and cause severe toxemia.
How? Soil contamination is the primary source because spores can survive for decades. Exposure can occur during grazing and with soil disturbance. Droughts, excavation and heavy rains can increase soil disturbance, therefore increasing exposure.
The sad part about blackleg is that the healthy, faster-growing cattle are usually the most susceptible and, in more cases than not, they are just suddenly found dead. If signs are observed, they can include sudden lameness, swelling in large muscle groups (thighs, shoulders, neck), fever and reluctance to move.
The most notable is a crackling sensation under the skin due to gas, also known as crepitus.
Treatment is rarely successful and animals found alive may receive high doses of penicillin, but survival is uncommon. Prevention is therefore the primary strategy.
Prevention. Vaccination is the most effective and widely used method. Calves are typically vaccinated at 2–4 months, with a booster 3–6 weeks later. Vaccines are inexpensive and highly effective.
How can we prevent blackleg from a management standpoint?
• Remove carcasses promptly to reduce environmental contamination.
• Avoid unnecessary soil disturbance that may expose buried spores.
• Maintain good nutrition to support immune function.
• Keep accurate vaccination records to ensure boosters are not missed.
Death of livestock is always difficult and can cause financial hardships for producers. Through proper management and prevention, we can minimize the profitability loss in our herds.
(Catelyn Turner is an Ohio State University Extension Agriculture and Natural Resource Educator.)
