Reprint from thc JOURNAL of the American Vetrinary Medical Association, Vol. 1417, No. t2, Dec., I5, 1965, pp. I377-86. http://users.erols.com/drrobert.sids/Calves.html

Robert C. Reisinger, D.V.M., M.S.

Summary

The pathogenesis of Escherichia coli diarrhea of newborn calves is the same today as when described so well by Theobald Smith and co-workers in the 1920's. There are multiple adverse contributing factors involved in precipitating this disease syndrome which vary from time to time and from area to area, but the pathogenesis of E. coli diarrhea of newborn calves remains the same. This will be true in later years when further research has given additional information as to the exact physiologic changes induced by presently known and as yet unknown adverse contributing factors, and to the various strains of E. coli involved. The newborn calf will not have changed (he will still be born into his world as naked on the inside as on the outside) and the pathogenesis of E. coli diarrhea in this animal will not have changed. The basic requirements necessary for prevention of diarrhea and death in problem herds and problem areas (which will be always with us) will remain the same, and will require (1) intelligent application of known husbandry and veterinary principles and method to ensure the birth of healthy calves into a favorable environment, (2) prompt feeding of colostrum, and (3) prompt and intelligent administration of appropriate drugs to offset both avoidable and unavoidable deficiencies which will arise from time to time in implementation of the first 2 requirements.

A visitor from another planet studying some of the literature on calf diarrhea published during the past several years might believe that the role of E. coli in the pathogenesis of this disease was just being discovered. Such is not the case. The classic work of Theobald Smith and co-workers from 1917 to 1930 ^52-62 clearly delineated the major aspects of the role of E. coli in the pathogenesis of diarrhea of newborn calves, including the protective role of colostrum. That work is as current and valid now as it was then. One reads reports of recent excellent studies which confirm various parts of this early work, although apparently the authors of such studies are often not aware that they are confirming previously reported experimental evidence. ^{9, 16} Others¹⁸ have questioned some of the findings because they differ from results of more recent but less extensive studies.⁶¹

While amply demonstrating the importance of the decisive role of E. coli in the pathogenesis of calf diarrhea Theobald Smith stated that there were other factors about which he knew very little which also played a part in this disease. In those days, technology did not include tools and methods to reveal obscure viral agents. Subsequent studies have revealed viral agents in some cases of calf diarrhea. ^{2,6,13,33-35,42,43,65} The observations⁵⁶ regarding the significance of quantitative and location factors in assessing the role of E. coli in the digestive tract of the calf with diarrhea have been fully confirmed.⁴³ In studies involving more than 60 calves,⁴³ quantitative cultures were made of the abomasum, 6-inch representative portions of the small intestine 10, 20, 30, and 40 ft. posterior to the abomasum, and the cecum and rectum of calves 1 to 10 days old which had been (1) apparently normal, (2) scouring, or suddenly dead or moribund without signs of diarrhea, (3) treated with chloramphenicol, and (4) treated with oxytetracycline. Coliform identifications were made, utilizing the replica plating technique³⁰ adapted⁶⁴ for screening intestinal coliform bacteria. Experiments also revealed the predisposing or contributing role of viral agents and of environmental stressors correlated with E. coli in the pathogenesis of this complex disease. Studies on bovine shipping fever have established that this syndrome is also a disease of complex pathogenesis involving various viruses, bacteria, and environmental stressors.^28,44,45

It has been observed that E. coli plays a similar role in pigs exposed to transmissible gastroenteritis (TGE) virus, by invading the upper intestinal tract of pigs exposed to TGE virus.⁶³ Transmissible gastroenteritis virus can cause death of newborn pigs, even "germfree" ones. However, it appears that in many cases of TGE infection in somewhat more resistant pigs. (i.e., those several days old and with variable amounts of antibody) which could survive TGE virus infection alone, multiplication and migration of E. coli into the upper digestive tract can be the determining factor in producing serious disease and death. These observations are supported by workers who isolated enteropathogenic strains of E. coli from pigs with TGE.^36,37 The usefulness of this method of assessing pathogenic strains was questioned since apparently another worker considered TGE a simple viral disease,¹⁸ rather than the complex disease which in reality it is.

An increase in coliform organisms and a decrease in gram-positive flora were reported in pigs with diarrhea.⁹ Exposure of young rabbits to cold resulted in intestinal E. coli overgrowth, enteritis, and death.⁶⁶

A recent monograph¹⁸ furnishes an excellent and up-to-date review of the literature on diarrhea of newborn calves. There are several omissions of pertinent work ( some previously unpublished ), some of which we will attempt to supply. In some cases our conclusions differ with those reported in the monograph.¹⁸ The more important of these differences are mentioned.

The Disease

Infectious diarrhea (scours) of newborn calves (9 to 10 days of age) is characterized usually by watery white or yellowish diarrhea, rapid onset and course, and high mortality. In affected calves diarrhea begins typically within 36 to 72 hours after birth, and the calves die within 2 to 3 days. Some calves may die several hours after having appeared healthy, without having any diarrhea at all.

The disease may affect most calves born in a herd, or may occur as a sporadic infection affecting only one or several calves while the rest remain well. Epizootics usually occur during the colder seasons of the year, but may occur during any season.

On the same farm or ranch and under the same apparent conditions of management, diarrhea may appear one year and not the next. Severity of the disease is known to vary considerably from year to year on given premises, even in an isolated herd.

Despite the many and varied studies undertaken regarding its cause, pathogenesis, prevention, and treatment, infectious diarrhea is still the major cause of death and illness in newborn calves, and often the major cause of economic loss to the raiser of beef and dairy calves.

Pathogenesis

The following facts must be considered to adequately understand, prevent, and treat diarrhea in newborn calves:

1 ) The calf derives no maternal antibody from its dam while in utero.^{1,15,18,26,31,32,38,43,54}

2) The calf is exposed to E coli, and to other bacteria and viruses, as soon as it is born. The calf is very often exposed to microorganisms, particularly E. coli, during its passage through the birth canal.^14,18,43,56

3) These organisms begin to multiply in the calf immediately. Escherichia coli organisms capable of being pathogenic exist on every farm and ranch and in every animal.^43,56 They are normally confined to the rectum, large intestine, and lower portion of the small intestine. ^43,56 The abomasum and approximately the first 30 to 40 ft. of the small intestine (where most digestion and absorption of nutrients occur) are normally acid and provide a suitable environment for the "benign" lactobacilli and enterococci which normally inhabit them. When these bacteria are established they, by their competitive physical presence and production of acid, help to create and maintain an environment inhospitable to E. coli. Lactobacilli are apparently normal inhabitants of the udder, since they are in raw milk, and also of the vagina.

4 ) The colostrum contains antibodies against those organisms to which the dam has previously developed some immunity. Colostrum may contain 15 to 20 times the concentration of protective antibody contained in the blood serum of the dam.

5) During the first several hours (approx. 6 to 24) of life, the upper portion of the calf's small intestine is highly absorptive.^18,26 This absorptive capability is not of an "on" and "off" nature, like an electric light switch, but is ever-decreasing. During this period, which nature apparently intended to allow absorption of the relatively large amount of antibodies contained in colostrum, toxins and other harmful substances can also be most readily absorbed.

6) Under "normal" conditions, a healthy calf partakes of colostrum within minutes after birth. Antibody begins immediately to be absorbed via the lymphatics into the general blood circulatory system and also spreads through the intestinal tract, limiting the growth and invasion of E. coli and other harmful agents. Lactobacilli from the colostrum and enterococci from the digestive tract of thc dam become established in the upper digestive tract, E. coli in the lower, and a healthy equilibrium is established (Fig. 1 ).

7) When colostrum is not taken by the calf immediately after birth, an alteration of this "normal" condition results. Escherichia coli organisms unhampered by colostral antibodies actively compete with enterococci, and the few lactobacilli which may have been collected by the calf on its way through the birth canal, for a place in the upper intestinal tract. If the calf is subjected to one or more additional adverse contributing factors (Table 1 and Fig. 3), the E. coli usually win and become the dominant flora in this absorptive portion of the intestine which is normally "off limits" to them (Fig. 2). As they go through the processes of multiplication and death, they release increasing amounts of highly potent and lethal endotoxin. Depending upon the potency and amount of toxin absorbed by the calf, varying degrees of illness, or death, ensue. Damages to intestinal epithelium may allow entry of E. coli organisms into the general circulation and internal organs. Some strains are more highly invasive than others, and can quickly gain entrance through apparently intact mucosa.^18,22 In other cases, with less invasive but highly potent strains, toxin may be so quickly absorbed from the intestinal tract that illness and death result from toxemia without bacteremia--often so quickly that death results without observed illness.

In the course of extensive studies on calf diarrhea, pathognomonic lesions associated with peracute deaths in very young calves could not be demonstrated.³⁴ Peracute deaths due to the "enteric-toxemic" form of E. coli proliferation in the small intestine, without bacteremia, have been reported in calves up to 6 months of age.²¹ It is apparent that in such cases, lacking pathognomonic lesions and with negative bacteriologic cultures of internal organs, unless various levels of the small intestine are examined quantitatively for E. coli the case will go undiagnosed, or be recorded as "sudden unexpected death" (SUD) of undetermined cause.

It is the multiplicity of number and degree of adverse contributing factors referred to which makes diarrhea of newborn calves such a complex and variable disease. These factors include (1) unavoidable rigorous weather conditions, and sometimes avoidable adverse management conditions, that result in exposure to cold, wind, and wet;^43,66 (2) subnormal nutritional state derived from the dam, including avitaminosis A;^4,25 (3) pathogenicity, concentration, and multiplicity of viral and bacterial agents to which the calf is exposed; (4) the time interval between birth and colostrum feeding;^6,34,43 and others.

These adverse contributing factors are inter-related. When the total effect of adverse contributing factors, including those just described in (1), (2), and (3) is small, the "allowable time" before first colostrum feeding is large--conversely, as the total effect of adverse contributing factors becomes greater, the allowable time between birth and first colostrum feeding becomes smaller, until it approaches zero (Fig. 3). For example, the time factor will not be as critical for a calf born on clean grass on a warm sunny morning from a healthy dam as for a calf born into mud and manure on a cold windy night from a dam with avitaminosis A or otherwise diseased.

8) If a calf receives colostrum after the chain of adverse internal events is underway, it may (1) recover without clinical signs (even subclinical cases may result in stunted calves, preventing their achieving optimal potential), (2) become clinically ill and yet recover, or (3) die, depending upon the total effect of adverse contributing factors, and upon others, many yet unknown. Once the chain of adverse events has begun, E. coli alter conditions in the anterior intestine, to a greater or lesser degree, to their own requirements, and it becomes increasingly difficult for lactobacilli and enterococci to become established. Escherichia coli may multiply to the extent that as many as 100 million to 1 billion may be demonstrated per cubic centimeter of intestinal contents even in the upper portion of the small intestine. On a quantitative basis, there may then be insufficient E. coli antibody in the colostrum to adequately cope with this vast number of organisms. Usually at this stage one of the many strains of E coli present will have asserted itself over the others and become numerically predominant. It is in this manner that the most highly pathogenic strains of E. coli are "selected out," and become the predominant flora in a calf, or in an epizootic. Ability to multiply quickly in the host is usually an inherent mechanism of pathogenicity in bacterial organisms--hence, when opportunity allows, the most highly pathogenic strains flow into the breach and become the predominant flora. This is one logical explanation of why the incidence of calf diarrhea may increase and the disease become more severe as calving season progresses. Pathogenic strains are selected out and have grown perhaps even more pathogenic.

When one, or even several, highly pathogenic strains predominate, there may result a quantitative antigen-antibody imbalance. Colostrum normally contains antibodies to many different types of E. coli. When only one or several types predominate, antibody against these types, while present, may be quantitatively insufficient unless given most promptly after birth of the calf.

Prevention

In clearly visualizing the condition existing in the intestinal tract of the normal calf and in one with diarrhea, one can understand that any factor which serves to upset the equilibrium between upper and lower bowel may result in disease. Overfeeding can result in dilution of the normal acid condition of the anterior portion, ballooning of the bowel, sluggish peristalsis, and a resultant forward migration of E. coli. Chilling and wetting can result in lowered vitality and suppression of normal peristalsis with the same result. Such factors in older calves are not as highly or quickly lethal, since the intestinal tract in these animals is tougher and less absorptive than in the 1- and 2-day-old calf.

Prevention of diarrhea and death in newborn calves must be directed toward establishing as rapidly as possible the normal bacterial flora and normal physiologic state within the intestinal tract.

Colostrum.--The greatest single factor for accomplishing normalization is early feeding of colostrum, preferably within 15 minutes after birth.^34,43 If fed within this time, the initial amount required is not great. Under experimental conditions 1/2 to 1 pint has proved sufficient. The key word is early.

"Prompt" feeding of colostrum has been, defined as "within 24 hours after birth''¹⁵ but this definition is not valid, at least not for this country. Studies in Wisconsin^33,34,43 have shown that many calves born during the winter months would have diarrhea if not fed colostrum within the first 2 hours or less after birth. In some calves, the ability to absorb, from colostrum, antibody to a somatic antigen of E. coli may be lost as early as 6 to 8 hours after birth.

Prevent Overfeeding.--For the first several days of life, feeding milk equal to 10% of the body weight per day is ample. This may be fed in 2 equally divided meals--for example, two 4-lb, feedings for an 80-lb calf. In cool, damp weather, calves will not require additional water for these first several days.

In problem herds, a temporary muzzle may be constructed of a piece of meta1 or plastic mesh and a piece of baling wire, with a piece of binder twine tied behind the cars for thc strap, to prevent overeating of milk and ingestion of straw and filth. Individual calf pens are, of course, preferable and are becoming increasingly more popular.

Antibiotics.--There is no adequate substitute for early feeding of colostrum. Adhering to the recommendation for early feeding of colostrum will sometimes require truly Herculean efforts, but the results will be worth the efforts and work involved. However, it is realized that under even the best conditions it will not be possible to get colostrum promptly into 100% of the calves. In cases of delay, depending upon the total effect of the adverse contributing factors, it may be necessary to administer an appropriate antibiotic simultaneously with the colostrum. Since E. coli organisms are gram negative and the benign lactobacilli and enterococci are gram positive, an antibiotic more selectively active against the gram-negative bacteria than against the gram-positive ones is required.

Chloramphenicol is such a drug.^{8,ll,24,34,43} While it may reduce the numbers of lactobacilli and enterococci to some extent, it is very quickly and highly effective against E. coli. The recommended dosage is 500 mg. per orum administered at approximately 12-hour intervals until 2 or 3 doses have been given. This will keep the E. coli bacteria in check until the calf's intestinal tract has become more resistant and less absorptive. The effectiveness of chloramphenicol is due to quickly eliminating E. coli from the small intestine, and even from much of the large intestine. Aerobacter species become the predominant flora in these areas, so that after chloramphenicol treatment is stopped, the E. coli must compete with these to re-entrench in even its normal habitat.

Parenteral injection of chloramphenicol is recommended also, if E. coli septicemia is suspected or confirmed. It must be remembered, however, that necessary antibiotic levels for required prompt destruction of E. coli in the intestinal tract cannot be achieved by parenteral injection, and that calves can readily die from absorption of toxins from the intestinal tract even in the absence of bacteremia. Thus, parenteral administration is an adjunct to, and not a substitute for, oral dosage. It should also be recognized that calves may develop pneumonia even while being given oral doses of chloramphenicol adequate to prevent or control intestinal infection, and supportive parenteral administration of penicillin-streptomycin combinations or other appropriate therapy should be administered when indicated.

The tetracycline group of antibiotics should not be relied on for prevention or therapy of diarrhea of newborn calves. A1though probably effective at one time, they have been so widely used clinically and as feed additives that many strains of E. coli are now resistant to them.^{3,24,27,49,50}

Contrary to some popular opinion and much illusionary advertising, there is no valid controlled experimental evidence to prove that feeding tetracycline supplements to calves decreases the incidence of diarrhea.

Calves allowed no colostrum but given 500 mg. of oxytetracycline twice daily from shortly after birth developed diarrhea and died slightly more quickly than similarly fed calves given no treatment at all.^34,43 In the guinea pig, "the normal gram-positive intestinal flora is inhibited in its development soon after the administration of penicillin, chlortetracycline, and bacitracin. The gram-negative bacilli overgrow other organisms of the intestinal tract, secreting toxins that paralyze the normal intestinal peristalsis," with resulting illness and death.¹² A similar condition appears to be elicited in certain instances in calves.

The writer's experience is specifically with chloramphenicol and the tetracyclines. Other antibiotics and chemotherapeutic agents' such as the nitrofurans,^{23,29,38,39,40} may be as effective in preventing diarrhea of newborn calves as is chloramphenicol.

The 3 criteria for selecting a preventive or therapeutic agent are: (1) it must act effectively against E. coli in the calf's digestive tract, not just in the uncomplicated environment of a bouillon tube or agar plate; (2) it must not destroy great numbers of the necessary lactobacilli and enterococci organisms; and (3) it must act quickly. Some drugs ineffective against diarrhea of newborn calves may be effective in treating older calves where the time factor is not so critical and the digestive tract is tougher and not so absorptive. But in preventing diarrhea and death in newborn calves, time is a highly critical factor.

One worker¹⁰ found a lower pH in feces of normal calves than in calves with diarrhea, and has had success in prevention and treatment of diarrhea with solutions of dilute acids. This is analogous to the farm remedy of "a coke bottle full (6 oz.) of vinegar," and of the extensive use of vinegar in human folk medicine in northeastern United States. This treatment may present excellent possibilities, since it would create an environment favorable to lactobacilli and unfavorable to E. coli. Furthermore, one would not expect development of resistant strains of E. coli, as must be anticipated with use of antibiotics.

Favorable results have been reported in some cases in calves and lambs following use of acidophilus milk.^46,47 This excellent and painstaking work was apparently the basis for some of the lactobacilli powders commercially available today. Although undoubtedly of benefit in some cases, including cases in which prolonged use of broadspectrum antibiotics has destroyed all or most of the normal gram-positive flora in the small intestine, action of the dried cultures is apparently too slow to be of decisive benefit in critical cases, and use of liquid acidophilus milk is unavoidably cumbersome.

Artificial Immunization.--It is theoretically possible that, in some instances, colostrum from most cows within a herd may be lacking in specific antibodies against certain E. coli strains in the herd environment. This might be expected to occur when there have been additions to a segregated herd recently enough so that cows have not had time to be exposed to "imported" strains, and so develop antibodies against them. However, definitive evidence is lacking that this is so, and that absence of specific colostral antibody in the dam is a critical factor in cages and epizootics of calf diarrhea usually encountered.

Bacterins containing killed cultures of E. coli and other Coliform organisms have been used for many years, inoculated into both cows and calves in the hope of preventing calf diarrhea. None has yet been proved effective.¹⁸ Killed cultures of E. coli are notably poor inducers of antibody production. There are many different strains, most of which are potential pathogens, and they mutate quickly on artificial mediums.⁵⁸ Even allowing for the possibility of an adequately antigenic autogenous bacterin prepared against certain strains in a particular herd, such a bacterin could hardly be expected to induce appreciable antibody production in time for the current calving season. The E. coli strains causing diarrhea during one calving season would not be expected to be the most prevalent troublemakers during the next. Furthermore, by the following calving season, the cows should have contacted the strains sufficiently in the environment to be naturally immunized against them.

In studies in Ontario, Canada, calves fed colostrum from unvaccinated cows were resistant to colisepticemia when challenged with an imported virulent strain, RVC 1787, even though some of these calves had no demonstrable agglutinins to RVC 1787 in their serum, and RVC 1787 has not been isolated from calves with naturally occurring cases of the disease in Ontario.²² Because "colostrum-fed calves are resistant to experimental infection with serotypes of E coli associated with colisepticemia regardless of the presence or absence in their serum of specific agglutinins against these serotypes," it was considered unlikely that lack of K agglutinins in colostrum or serum was an accurate indicator of lack of protective antibody.^l8 Other workers found no relationship between bactericidal activity of the serum and resistance of the calf.²³

The greatest proportion of diarrhea in newborn calves appears due, not to lack of specific antibody in colostrum, but to lack of promptness in its administration, coupled with a variety of adverse contributing factors.

Husbandry Practices.--Trite though it may sound, the ultin1ate prevention of diarrhea and death of newborn calves entails having a healthy, vigorous calf born to a healthy well-nourished dam under excellent environmental conditions--facts well demonstrated and documented in past ranching, farming, and research experience. This simple statement encompasses all phases of animal husbandry and veterinary medicine.

As stated before, if the total of adverse contributing factors becomes great enough, the allowable time for feeding colostrum approaches zero. It must be recognized that environmental conditions can become so impossibly inadequate they cannot be overcome. No presently known measures, nor any capable of being developed through the most thorough and adequate research, can prevail against them.

"Instead of having to endeavor to control disease under impossible conditions, it should, by proper planning, be possible to develop intensive management systems which are both favorable to the animal and adequately hygienic "⁵ For the rancher and dairyman to accept this statement, this philosophy, he must know why, and we have the responsibility to adequately explain why in specifics, not generalities. If, as is becoming increasingly the case, the cattleman chooses to have his cows bred so that they calve early in the year in hopes that he will have heavier calves to market as feeders, he must be given adequate and understandable facts, so that he may know beyond a shadow of a doubt exactly why, if unfavorable weather conditions prevail during calving season and there is not adequate shelter for his calves, his losses may well be high. At the same time he must be given information as to what he can best do under the circumstances to, as far as possible, reduce these losses. He must bc told beforehand that if the previous summer was dry and hot, and his hay is, therefore, weedy and low in vitamin A and other essential components and the calving season is co1d,windy and wet, and his cows have been brought into relatively small pastures or lots where proximity favors selection of particularly virulent strain" of E. coli and fosters spread of various viral agents, he had better be riding or walking night-herd (and day-herd) to see that calves get early colostrum and shelter, and in some cases promptly administered appropriate antibiotics. There is no easy way.

Workers have demonstrated a viral agent (calf pneumonia, enteritis virus) in the lungs of normal cattle, and reported that during the winter months this agent became concentrated in the relatively closed and humid atmosphere of dairy barns.⁶ Calves born into this atmosphere and not promptly given colostrum had diarrhea and usually died. Another worker confirmed the latter observation⁴³ and further demonstrated that calves born outside during the winter months, not given colostrum and not dried, and placed inside a clean isolation unit maintained at approximately 45 F., had diarrhea and died. Large numbers of E. coli were found in their anterior intestinal tracts, and in one instance in spleen and heart blood. Calves treated similarly, except that they were promptly rubbed dry with absorbent cloth sacking rinsed in hot water and squeezed as dry as possible, remained healthy and had no diarrhea. It is postulated that these 2 situations are analogous to those which occur when a calf is born and its dam either (1 ) immediately wanders off for a variable time or (2) remains to nuzzle and lick the calf dry and allows it to partake of colostrum.

We are told that early calving is a question of economics. Some years ago we were told that winter racing for 2-year-old Thoroughbreds was a question of economics. There was very high attrition among these 2-year-olds. There was a complete numerical turnover of horses in training on the race track approximately every 3 years-- 27,000 horses were in training on all tracks, and about 9,000 Thoroughbred foals were registered each year. There was very little or nothing that we, as veterinarians, could do to stop this attrition. We were working against reason and nature with people who were trying to do something that could not be done. There has been a marked decrease in winter racing of 2-year-olds over the past several years. The reason is called economic. It was finally realized that a 4 1/2-furlong race contested by erratically running youngsters was not a particularly interesting spectacle or favorable wager for the bettors, and also that perhaps the economic cost in crippled youngsters was too high. So now the trend is reversing primarily due to what is called economics.

The veterinary profession has no authority to determine how any person will manage his livestock. This is determined by each individual's ideas or interpretations, as long as his individual "economics'' will stand it. But our profession does have the responsibility to explain to the rancher, dairyman, or other animal owner, as clearly and as objectively as possible, the probable health and disease results and consequences relating to various husbandry practices.

It is appropriate here to quote from the words of Theobald Smith, "The achievements of science are neutral, until applied by man for purposes constructive or destructive, good or evil."^30A Research on diarrhea and death of newborn calves should be continued and expanded. But while we are seeking further answers, we must apply all available knowledge, which is considerable, to solving present problems.

References