PREVENTING CALF SCOURS IS DIFFICULT BUT IMPORTANT TO HERD MANAGEMENT

by: Stephen B. Blezinger
Ph.D., PAS


There are few herd health issues that create the level of problems and cause the degree of financial loss to the cow calf producer as that created by intestinal infections and the related scouring in calves. Interestingly, scours, or extreme diarrhea as it can be otherwise termed is not uncommon at all and can be attributed to a variety of conditions. In older calves or cattle, in some cases, it can be caused by a change in the diet, for instance when cattle go from being fed dry hay to grazing lush grass or legume pastures in the winter or spring. Other dietary changes that can produce a similar result may be seen when cattle are changed from a high forage diet to a high grain diet and the appropriate steps are not taken to make this change gradually enough to prevent a digestive upset.

The type of scours or diarrhea to be addressed here is not caused by a dietary change but the more serious type created by an infection of the digestive tract. It is also not a disease in and of itself at all but a symptom of disease that can have a variety of causes. Feces in calves with scours are typically very watery, the result of the stools having a much higher liquid content than is normal. While the feces of very young calves is generally fairly soft due to the fact that they are on a liquid diet for the first weeks of their lives, an infection of the intestinal tract resulting in an inflammation of the tissues. This results in a rapid, higher volume discharge of fluids from the body. This is a problem in the young calf since this animal is about 70 percent water and the rapid loss of fluids can rapidly lead to dehydration. The fluid loss is also accompanied by the loss of electrolytes such as sodium, potassium, magnesium. This results in a change in the calf's body chemistry and is generally considered the actual cause of death in severely affected calves.

The remaining focus of this article is to take a more in-depth look at the causative organisms and surrounding issues.

Basic Causes

As mentioned above, diarrhea is common in newborn calves. It is common in all young ruminants including lambs, and kids. The acute disease is characterized by progressive dehydration and death, in some cases as soon as within 12 hours of onset. In the less severe or subacute form, diarrhea or scouring may continue for several days and result in malnutrition and emaciation.

An enteropathogen is an organism that is capable of producing a disease in the intestine. There are several enteropathogens associated with diseases in the neonatal calf that can result in diarrhea. Their prevalence, for the most part, varies geographically, but the most prevalent infections in most areas are Escherichia coli, rotavirus, coronavirus, and Cryptosporidium parvum. Cases of neonatal diarrhea are commonly associated with more than one of these agents, and the cause of most outbreaks results from a variety of factors. Determining the particular pathogen causing an outbreak of diarrhea can be important because specific therapy is available for some. In some cases the problem here is magnified due to the fact that some organisms can be transferred to humans where a subsequent infection can occur. Let's discuss some of the more common infective organisms.

Bacteria

E coli is the most significant bacterial cause of diarrhea in calves. There at least two distinct types of disease resulting in diarrhea produced by different strains of this organism. One type is associated with enterotoxigenic (producing a toxin in the digestive tract) E coli which has fimbrial antigens which enable them to attach to and colonize the villi (finger-like projections) of the small intestine. These enterotoxigenic E coli also produce an enterotoxin that influences intestinal ion and fluid secretion to produce a diarrhea not related to tissue inflamation. Diarrhea in calves also has been associated with enteropathogenic E coli that adhere to the intestine to produce lesions, with a breakdown of the brush border and loss of microvillous structure at the site of attachment. More simply put, these bacteria attached to the tissues of the intestine causing lesions which are the result of a breakdown and “sloughing off” of these outer layers which are normally involved in nutrient absorption. This also results in a decrease in enzyme activity, and changes in ion transport (mineral absorption) in the intestine. These enteropathogens are also called “attaching and effacing E coli.” Some produce a “verotoxin,” which may be associated with a more severe hemorrhagic diarrhea. The infection most frequently is in the cecum and colon (large intestine), but the later segments of the small intestine can also be affected. The damage in severe infections can result in edema and mucosal erosions and ulceration, leading to hemorrhage into the intestinal lumen. In cases such as these it is common to see a bloody discharge or blood in the feces.

The Salmonellas, especially S typhimurium and S Dublin, as well as other strains, cause diarrhea in calves ranging from 2 to 12 weeks of age. Salmonellae produce enterotoxins but are also invasive and produce inflammatory change within the intestine. In calves, infection by Salmonella commonly progresses to bacteremia or the presence of bacteria in the blood.

Other bacteria such as Clostridium perfringens types A, B, C, and E produce a variety of “tissue killing” (necrotizing) toxins and cause a rapidly fatal hemorrhagic enteritis in calves. Fortunately the disease in calves is fairly rare and usually sporadic. Infection with type B or C is also a common cause of enteritis and dysentery. Campylobacter jejuni and Yersinia enterocolitica may be present in the feces of calves and lambs with diarrhea but also may be found in the feces of healthy animals. This creates some speculation as to the how problematic these organisms truly are unless in the presence of another challenge such as stress.

Viruses

Rotavirus is the most common viral cause of diarrhea in young ruminants. Groups A and B rotavirus are involved, but group A is most common and clinically important and contains several strains which differ in virulence. Rotavirus replicates in the mature absorptive and enzyme-producing surface cells (enterocytes) on the villi of the small intestine, leading to rupture and sloughing of these cells. Subsequently this results in a release of viruses that can and will infect adjacent cells. Rotavirus does not infect the immature cells of the crypts. With the disease producing strains of rotavirus, the loss of enterocytes exceeds the ability of the intestinal crypts to replace them. This then means that as the population of villi in the small intestine is reduced there is a in intestinal absorptive surface area and intestinal digestive enzyme activity. Overall, this means greatly reduced digestive function.

Coronavirus is also commonly related to with diarrhea in calves. This organism differs in that it replicates in the epithelium of the upper respiratory tract AND in the surface cells of the intestine, where it produces similar lesions to rotavirus but also infects the epithelial cells of the large intestine to produce atrophy of the ridges in the colon.

Protozoa

Cryptosporidium parvum is a common cause of diarrhea in calves (especially dairy calves) and lambs. The parasite does not enter the cells or tissues of the intestine but adheres to the exposed surface of enterocytes at the far end of the small intestine and the colon. This results in losses of intestinal villi, decreased mucosal enzyme activity and fusion of the villi which leads to a reduced surface absorptive area. Finally inflammatory changes in the submucosa are commonly seen. Cryptosporidia is not host specific in mammals which means it can infect other species besides calves. This can include dogs, cat, horses and people.

The more well known (and expensive) diarrhea-causing disease in the beef industry is coccidiosis, caused by coccidia organisms such as E zuernii, E bovis, and E auburnensis. Experimentally, other species have been shown to be mildly or moderately pathogenic. Coccidiosis is commonly a disease of young cattle (from one to two months to one year of age) and is usually sporadic during the wetter seasons of the year. Conditions such as “summer coccidiosis” and “winter coccidiosis” in range cattle probably result from severe weather stress and crowding around a limited water source. This concentrates the hosts and parasites within a restricted area. Although severe outbreaks have been reported in feedlot cattle during extremely cold weather, cattle confined to feedlots are susceptible to coccidiosis throughout the year. Outbreaks of this type commonly occur within the first month after entry into the feedyard. The typical incubation period is 17-21 days.

A significant problem with infections by one organism or another is that calves can experience concurrent infections. These “follow-up” infections may more severely affect calves than normal due to the initial effect of the primary organism and subsequent damage to the intestinal tract and a weakened immune system.

Preventative Measures?

There are essentially two factors that prevent the calves from developing diarrhea (scours), becoming ill and dying. One is the dose or amount of the infectious agent(s) received. The higher the dose in the environment of the calf the more likely the calf will be exposed to the agent(s) and become ill. As such, sanitation is very important in keeping the dose low. Calving the cows in clean fields or pastures is very helpful and keeping the cows spread out (low density) is also important. The second important factor in preventing scours is the immune system of the calf. The calf's immune system has two important facets: (1) the ability of the individual calf to resist disease, and (2) the colostrum the calf receives from the cow soon after birth. Both of these factors are dependent on good quality nutrition before the calf is born.

Scour Vaccines?

Yes, there are some excellent vaccines for Rota virus, Corona virus, and E. coli K99. These are given to the pregnant cows/heifers during the last three months of pregnancy. Remember, these vaccines stimulate the cow to make antibodies that are then transferred to the colostrum, so if you short the cow on protein or other nutrients which involve the immune system the vaccine (or any other vaccine) will not do its job for you. At the present time there is no effective vaccine for Cryptosporidium on the market.

Other Management Tools

The important ideas here are sanitation and isolation to help prevent calf scours. Here are a few areas to be aware of in a prevention program. These are also good tips for your operations biosecurity in general.

1. Calve the heifers earlier than the main cowherd in clean fields. The heifers have lower quality colostrum and lower amounts. Their calves are more susceptible and isolation is helpful.

2. Try to calve at a time of year when it is not wet or muddy in the calving pastures.

3. Do not bring in outside cattle during the calving season. These cattle can be the source of diseases your cattle have no immunity against.

4. Use strict sanitation when treating sick calves. Treat sick calves only after handling the well       calves — never before. Disinfect all balling guns or esophageal feeders after treating sick calves, use disposable gloves, wash your clothes and equipment after treating scouring calves, etc. You can carry the “bugs” on your gloves, clothes, and equipment from a sick calf to a healthy calf. Thus, you can become the cause of an outbreak and not the cure.

5. Isolate sick calves and their cows to a separate field or area to avoid the build-up of pathogens in the main cowherd.

6. Try to avoid feeding hay when the calves are very young (granted, this may be impossible). This concentrates the cattle and their feces on the hay feeding areas and increases the load of “bugs.” Use of good pastures or fields put aside during the first two to three weeks of the calves' lives is a good idea. Feeding cottonseed meal (or soybean meal) with 30-40 percent salt in feeders can be a successful way to supplement during this time.

Conclusions

Preventing calf scours is an important part of management; however, it is not simple to accomplish. Feeding the pregnant cows and heifers is a very important part of this equation that is sometimes overlooked. Your veterinarian and nutritionist can provide you with additional helpful information that is specific to your herd.

Steve Blezinger, Ph.D., PAS is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached by phone at (903) 352-3475 or by e-mail sblez@verizon.net.







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