Common Pathogens Causing Diarrhea in Dairy Calves

Introduction

Diarrhea is associated with more preweaning dairy calf deaths than any other disease. It is important to understand which pathogens are associated with calf diarrhea, and which cleaning agents are effective against different pathogens to sanitize the calf’s environment [1]. Calves with diarrhea have a fecal consistency that is either watery or loose and sifts through bedding [2], Figure 1. Infection occurs via the fecal-oral route [3]. Several pathogens are responsible for diarrhea in preweaned calves including bacteria, viruses, and protozoa [3], Figure 2. The most common pathogens responsible for diarrhea in calves are viruses such as bovine rotaviruses and coronaviruses, protozoa such as Cryptosporidium parvum, and bacteria such as E. coli spp.,Clostridium perfringens, and Salmonella spp. [4]. This article covers common pathogens associated with calf diarrhea and sanitation methods to sanitize the environment to kill specific diarrheic pathogens.

score 0 = normal (solid)
score 1 = yogurt consistency
score 2 = pancake batter consistency (abnormal)
score 3 = orange juice consistency (watery, diarrhea)

What happens when calves experience diarrhea?

Calves that experience diarrhea have cell death in the small intestine leading to impaired nutrient absorption and excessive liquid secretions from the small intestine which cumulatively causes dehydration [3]. Provide fluid replacement therapy, such as electrolytes, to keep on top of dehydration in diarrheic calves [4]. Concurrent infection, when calves are infected with two or more pathogens, is commonly reported in diarrheic calves [5, 6]. Data collected during the most recent USDA survey observed that producers treated 68.8% of diarrhea cases with antimicrobials, yet many cases of diarrhea were not caused by bacterial infection [7]. Dairies must take fecal samples on healthy and sick calves during an outbreak to evaluate which pathogens are commonly associated with diarrhea in the herd.

Viruses

Rotaviruses are extremely common in young calves and have a very short incubation period of roughly 12 to 24 hours after infection [8]. This virus often infects calves before 2 weeks of age and leads to malabsorptive diarrhea due to intestinal damage and the toxins released by the virus [5]. Rotaviruses can remain infectious for extremely long periods at regular room temperatures [8]. Chlorine bleach at 1750 ppm and environmental temperatures above 60° C kill rotavirus, as does 3% hydrogen peroxide, phenol, formalin, and quaternary ammonium compounds [9]. One way to minimize the impact of rotavirus infections is to work with your veterinarian to create a vaccination plan that includes a rotavirus vaccine in your dry cow program. A dry cow vaccination program provides specific antibodies in the colostrum to allow for better protection if a calf is exposed to the virus.

Coronaviruses are another common diarrheic pathogen identified in healthy and sick calves [10]. Most cases will occur in calves between 5 to 10 days of age; however, calves up to 30 days can become clinically ill [10]. Adult cattle can be carriers [11] and fomites like clothing and equipment can spread this disease easily [3]. Diarrhea in coronavirus cases is characterized by feces containing blood and mucus [3].  This virus is susceptible to most disinfection agents containing phenol, formalin, quaternary ammonium compounds, bleach, and hydrogen peroxide; however, coronavirus can live in the soil for up to 3 days [11]. Therefore, calf manure must be removed before disinfection to eliminate this virus in the calf’s environment [11]. One step to controlling coronavirus is to work with your veterinarian to implement a vaccine into the dry cow program.

Protozoa

Protozoa are single-celled organisms that invade a living host to reproduce [12]. Cryptosporidium parvum(Crypto) is a parasitic protozoan species where calves experience the infection around 7 to 90 days of age and have compromised feed efficiency for the duration of the infection [13]. Diarrhea caused by this pathogen is usually watery and can often last for several days [3]. Only 10² oocysts are needed for infection, about the size of a teaspoon of fecal matter [13]. Infected calves can shed the oocysts for weeks after the initial infection [13], making it extremely difficult to eliminate from a calf barn [14].  Currently, there is no FDA-approved preventative for Crypto, so it is imperative to maintain a clean environment to prevent Crypto outbreaks in calves [3]. Crypto is a zoonotic pathogen, so biosecurity practices such as handwashing, boot washing, and changing clothes before leaving the farm prevent the spread of infection to your family and employees [3]. The only agent that destroys the cysts is 3% to 6% hydrogen peroxide solutions with 20 minutes of contact time, and a drying period [14]. However, hydrogen peroxide is flammable and corrosive, so proper personal protective equipment should be worn when using this chemical [14].

Bacteria

Enterotoxigenic E. coli (ETEC) almost exclusively infects calves under 5 days of age [3-4]. Calves can become infected by swallowing manure during parturition, especially during dystocia, or from dirty maternity pens, contaminated colostrum, or poorly maintained colostrum feeding equipment [3-4].  A calf who ingests feces before colostrum feeding is at an increased risk of E. coli infection, and is less likely to achieve successful passive transfer of immunity status from the colostrum [3, 15]. This pathogen causes secretory diarrhea, meaning that the cells in the intestinal wall secrete extra mucus [5]. Because less mucus is excreted, damage to the intestinal cells is less of a concern, but in consequence, dehydration occurs rapidly in these calves [3, 16]. Calves infected with ETEC are at greater risk of sepsis because of the toxins secreted by ETEC; this leads to systemic signs of illness such as fever, and poor recumbency though some of these signs are rare [17]. Antimicrobial treatment is often warranted during severe infections, but work with your veterinarian to make these decisions. Focus on regularly cleaning the maternity pen, and keep colostrum feeding equipment well maintained to control this disease [3]. For example, if an esophageal feeder has bite marks down the tube toss it out as this is a reservoir for ETEC bacteria. Disinfection of calf housing, feeding equipment, boots, and clothing can prevent outbreaks [3]. Most disinfectant agents are effective at killing E. coli, consult the label of the product being used to ensure contact time is sufficient [18]. One step to controlling ETEC is to work with your veterinarian to implement a vaccine into the dry cow program.

Salmonella spp. infects calves throughout their life cycle, but many Salmonella infections related to diarrhea in calves occur when they are under one month of age [3]. Salmonella typhimurium is a common cause of diarrhea in calves [5]. Being an open herd is a known risk factor and increases the likelihood of infection on the farm. According to the most recent USDA survey, the prevalence of Salmonella spp. was 28% in dairy cattle [7].  Salmonella invades cells by waiting for the immune system of the calf to be weakened [5], meaning that calves with poor passive immunity status or prior infections are most likely to be infected. All species of Salmonella are frustrating to manage once they are in a barn because many animals silently shed the pathogen as carriers without outward clinical signs of disease [5]. Clinical cases shed the pathogen for weeks after the calf resolves the infection so good sanitation practices are fundamental to reduce the spread of the disease [5]. Salmonella spp. are also zoonotic, thus strict biosecurity practices are imperative to protect employee health and reduce the likelihood of transmission [15]. Most Salmonella spp. are susceptible to cleaning agents including alcohol, chlorhexidine-based products, hydrogen peroxide, and chlorine-based disinfectants [18]. A contact time of 10 minutes and sufficient rinsing and drying time are crucial to successful disinfection [18]. If a farm has a Salmonella Dublin outbreak, allow a few days of barn rest before restocking the barn with new naïve cattle if possible.

Clostridium perfringens is a bacterium native to the gastrointestinal tract of calves, but an overgrowth can cause bloating and death in a matter of hours [3]. The most common cause of bacterial overgrowth is improper nutritional management of young calves [19], such as feeding milk at the incorrect temperature or incorrectly mixing milk replacer. This can lead to an overgrowth of the bacteria and the production of toxins, which are what ultimately cause diarrhea from the cellular damage incurred [5]. The type of toxin created depends on the strain of Clostridium [5], so testing is required to determine the specific strain or toxin responsible. Prevention practices can include vaccination [19] or using a milk replacer with a coccidiostat such as Lasalocid [20], which helps inhibit the overgrowth of Clostridium. Proper nutritional management is the easiest way to reduce mortality due to this bacteria.

Several pathogens are associated with diarrhea in calves, but knowing what is causing diarrhea cases in your herd is the first step in managing and controlling it. Diarrhea can wreak havoc on preweaned calves’ health and productivity. However, simple biosecurity, prevention, and disinfection practices can protect your herd from diarrhea-related losses.

References

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