Winter dysentery in cows: The causes and methods of control
Winter dysentery in cattle
For many cattle farms, the winter season can also bring with it an unwanted side effect: winter dysentery. Incidences of winter dysentery in cows often increase between November and March, when environmental temperatures are generally at their lowest, because the virus is highly resistant to freezing temperatures [1, 3].
What causes winter dysentery?
Winter dysentery is caused by a bovine coronavirus, which is also associated with calf diarrhea and shipping fever pneumonia, among other diseases . Beef and dairy cattle of all ages can be affected by winter dysentery, but it is more prevalent in adult dairy cows and more common in those that have recently calved . Winter dysentery is highly contagious; after the first animal gets sick with the disease, it spreads quickly to other animals within a few days.
Generally, winter dysentery has been known to affect 30–50% of a herd, but in some cases, it has affected up to 100% of the animals in a herd . The risk of death in animals affected by winter dysentery is low, ranging between 1–2%. That risk increases, however, for animals that are affected by secondary bacterial infections .
How is the winter dysentery virus transmitted?
The winter dysentery virus can infect the digestive tract, including the large and small intestines, as well as the respiratory tract and the lungs [2, 4]. After the infection is established and the virus has spread to the animal’s digestive and/or respiratory tract, the virus is released into the environment via the feces and/or nasal secretion for a period of one to four days . Healthy animals coming to contact with contaminated feces and nasal secretion is responsible for new infections.
What are the symptoms of winter dysentery?
Some animals do not present with symptoms of winter dysentery despite being infected with the disease. This can become a problem for producers, because if animals are not identified as being sick, they will continue spreading the disease to other healthy animals in the group/pen.
Some of the most notable signs that a cow has been afflicted with winter dysentery include acute diarrhea, manure with a liquid consistency and even visible blood in the feces. Once an animal is infected, they will begin showing these symptoms — as well as a reduced feed intake and a drop in milk yield — between three to eight days later .
On their first day the symptoms manifest, animals generally present with mild diarrhea characterized by loose consistency and increased frequency. In the following days, the symptoms often evolve to more severe diarrhea and dysentery . The colour of the feces can vary from dark green and/or dark red to almost black. The diarrhea episodes are described as projectile , and the diarrhea symptoms usually last for 4 to 7 days .
Some animals struck with winter dysentery may show signs of abdominal pain or colic, including an arched back or hunched-up appearance . In severe cases, animals also present with dehydration and weakness . The virus can also infect the lungs — and if that is the case, animals usually present with respiratory symptoms, such as cough, difficulty breathing and/or nasal discharge .
Due to the way it affects the body, animals experiencing winter dysentery often have impaired gut integrity — meaning that the cells on the surface of their intestines could be damaged, resulting in increased permeability in the gut. This increased permeability is problematic because it means that the gut can absorb more toxins while also experiencing a reduced absorption capacity for useful components, such as nutrients. In severe cases, a loss of surface epithelial cells, necrosis and the desquamation of crypt epithelial cells in the large intestine have also been observed , further compromising nutrient absorption and, in turn, the animal’s performance.
Animals that are affected by winter dysentery can experience a significant drop in feed intake, which subsequently leads to a drop in milk yield in those animals, as well as a decrease in their body weight and reduced body condition scores . Although their feed intake generally returns to the levels observed before the disease, milk yield takes longer to bounce back, and the cow’s production levels may not ever reach their pre-infection levels again . In some cases, as a consequence of their impaired immune response, animals affected by winter dysentery become more susceptible to other infections, which could extend their recovery time.
When animals are cured of winter dysentery, their feed intake recovers fast. However, milk production takes longer to recover, and the cow’s production level may not ever return to what they achieved before the disease.
While winter dysentery does respond to most conventional disinfectants, there is not any official treatment for it, and the negative impact it can have on a cow’s milk yield can last for several weeks while the animal recovers from diarrhea and other exhausting symptoms. The many negative characteristics of the disease can have a major impact on animal performance and, subsequently, can lead to significant economic consequences for an affected farm.
Risk factors for winter dysentery
Some factors could contribute an increased probability of a cow contracting winter dysentery. These factors include:
- The age of the animal (animals between 2 to 6 years old have a higher risk)
- Larger herd sizes
- Cattle in close confinement
- The use of manure-handling equipment for feed
- Poor barn ventilation
- A history of previous outbreaks in the herd
In a study of the risk factors for the development of winter dysentery, visits from veterinarians, artificial insemination technicians and bulk milk transporters were not associated with disease outbreaks .
Preventing and controlling winter dysentery
Because winter dysentery is caused by a virus, no specific treatment for it exists. However, the herd veterinarian should be contacted to evaluate the best support treatments for the secondary symptoms of dehydration and/or pain, as well as to observe the herd for signs of any secondary infections.
Reducing the risk factors for the herd and improving their gut health and immune responses are the best approaches to mitigating the spread of winter dysentery in cows. Other methods that can be utilized to decrease the risk of contracting the virus include:
- Following proper hygiene protocol
- Taking measures to avoid manure contamination in water and feed bunks
- Not using the same equipment for manure handling and feed
- Quarantining new animals in the herd
- Improving barn ventilation
- Staying vigilant and aware of any cows presenting with symptoms of winter dysentery
Including feed additives in the diet also has the potential to improve gut health and, as a result, could help animals get through an outbreak of winter dysentery with less stress.
The use of mannan-rich fractions from yeast in a herd’s diet can help support their gut integrity and optimize animal performance. This bioactive fraction derived from yeast has been shown to support nutrient utilization, help maintain digestive function and improve animal performance . Mannan-rich fractions also work to improve immunity, which helps animals build their defences against infection, including infection by the winter dysentery virus. These products also help decrease the risk of secondary infections, as they can reduce the number of pathogenic bacteria in the gut .
Talk with your nutritionist about using feed additives to help prevent and control incidences of winter dysentery in your herd.
Additionally, utilizing mycotoxin binders can be a good strategy, because exposure to challenged feedstuff can increase a cow’s susceptibility to disease and, as a result, could exacerbate the negative impact of winter dysentery.
Winter dysentery has a negative effect on animal health, thereby compromising animal performance. This disease spreads quickly and threatens to infect the whole herd, which would have a significant and lasting economic impact.
The best strategy for avoiding economic losses is to prevent the occurrence of winter dysentery in the herd. As such, reducing the herd’s risk factors and improving animal health can help diminish the negative consequences of the disease.
Alltech, a leader in animal nutrition, provides a full line of nutritional feed additive solutions to help address some of the biggest challenges for dairy producers in Canada.
Talk with your nutritionist about utilizing feed additives to help improve animal health and mitigate the negative impact of an outbreak in your herd.
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