Have you ever asked a dairy farm owner or manager, “What are the things that keep you up at night?” Or, if you are a dairy farm owner or manager, how would you respond to this question? I would expect responses relating to employee retention and labor concerns, current and future milk pricing or possibly future planning for growth and/or sustainability of the farm. I may get some answers that are more specific to milk yield issues, crop health or possibly manure management concerns. Most assuredly, not one person would respond with winter dysentery to this question.
Despite this seeming lack of concern regarding winter dysentery, nearly every dairy farm has, and unfortunately will have again, a winter dysentery disease outbreak. Winter dysentery is ubiquitous worldwide where cattle are present. Studies report on-farm clinical incidence rates anywhere from around 5% to well over 50% of a lactating cow herd can be affected by this contagious disease on an annual basis.
First-lactation heifers are often affected more severely by the profuse diarrhea-causing infection, reducing their milk production by 20% to 25% for several days during the peak of infection. Another cohort of animals often impacted by winter dysentery are aged cows that have eluded annual exposure for a few seasons. Previously acquired immunity to this disease for this population has waned and, just like the 2-year-olds, an immune-susceptible population will be affected more severely once they are exposed. In these populations, fevers spike, feed intake drops and projectile diarrhea develops that persists for three to 10 days for an individual animal.
For a herd, the entire duration of a winter dysentery outbreak can last two to three weeks before manure and herd performance return to normal. Those who have experience milking in a tail-to-tail stanchion barn know just how projectile that diarrhea can get, often reaching into the center aisle, some even reaching their herdmates on the other side of the aisle.
Winter dysentery is a contagious, infectious, diarrhea-causing disease in adult cattle caused by bovine coronavirus (BoCV) infection. The colloquial name, winter dysentery, comes from the fact that this malady generally occurs during the colder winter months of the Northern Hemisphere where barns are more tightly sealed up to accommodate the colder outdoor temperatures. Traditionally, cows would be kept inside rather than turned out on pasture, likely creating an environment of cool, humid air with animals housed more densely together, setting the stage for the virus to become more active. Although modern dairy farms have drastically changed housing conditions from when winter dysentery was first named in the 1940s, freestall-housed herds still experience winter dysentery breaks.
While this infection can affect a large number of animals on any given dairy farm, most cows show little to no symptoms and recovery is spontaneous for most animals. As previously mentioned, immune-naïve animals may exhibit more severe symptoms beyond diarrhea, including bloody diarrhea, reduced feed intake and rumination, moderate fever and possibly secondary infections including mastitis or pneumonia due to their compromised immune state. The good news is that while a large proportion of the herd might become infected, most often only minor clinical symptoms are noted and death loss is rarely, if ever, attributed to this disease.
Typically, after describing the disease and the agent that causes it, most authors would go into strategies to reduce the spread of infection by cleaning contaminated surfaces or isolating affected animals. However, these are not realistic options on a modern dairy farm. The author may discuss therapies to treat those most affected and, if vaccines are available, strategies to vaccinate prior to infection so that immunity can be established before exposure. However, as stated previously, this virus is on nearly every farm, and a population of cows on nearly every farm is going to experience some degree of symptoms, to which they will spontaneously recover after a few days; vaccines are not a practical option. So I will only mention that treatment of affected animals should include supportive care such as fever-reducing medications, gastrointestinal (GI) tract supportive care (probiotics) and therapies that boost hydration to counter fluid loss.
Winter dysentery is one of many challenges dairy herds face that is unpredictable but an unfortunate reality. Dairy farmers can’t know when winter dysentery will hit, just like many other infectious or non-infectious challenges dairy herds face. However, at various time points throughout the year, there will be something that will challenge the herd’s ability to function normally. It could be increased loose stools due to a poorly fermented silage pile, a mastitis that lingers and fills the treatment pen or a pneumonia outbreak that impacts the cull rate more than expected. Regardless of the challenge, every dairy farmer can relate to the unpredictable but reliable concept, which is why maintaining a healthy GI tract is important every day. If the cow’s rumen is healthy and the rest of the GI tract is functioning optimally, the likelihood of the individual and the herd managing through challenges greatly improves.
One way to maintain a normally functioning GI tract every day is to include a science-based, research-proven probiotic in the ration. Every animal, every day. Probiotics are viable bacteria or live yeast organisms that, once consumed by your cow, become active and multiply, conferring a positive effect on the animal. Some probiotics have been proven to improve mucus production in the small intestine, an important barrier to shield the animal’s body from unwanted GI pathogens. Some probiotics have demonstrated influence on the animal’s immune system to more rapidly respond to negative stimuli (i.e., mycotoxins, pathogens, etc.), even in areas beyond the GI tract (i.e., respiratory and reproductive tracts). Finally, some probiotics directly interfere with known pathogenic bacteria commonly found on dairy farms, including clostridium and salmonella.
Winter dysentery is only one of countless encounters dairy owners and managers combat while trying to maintain a healthy and productive dairy herd. And while there are very specific mitigation strategies for some challenges, other challenges are dealt with on a case-by-case basis. Winter dysentery, among others, is a disease that may fall into the unpredictable-but-reliable category – one cannot predict when it will hit, but sooner or later it will. For these types of situations, consider using a tool that can be working in every animal, every day to support a normal GI tract so that when that next challenge happens, you’re starting with a herd of healthy, functioning, productive animals. Daily feeding of an effective science-based, research-proven probiotic will support your herd through the inevitable ups and downs of dairy farming.
