Feedlot Diseases of Cattle and Sheep

Lecturer: Dr. Don Montgomery

With some exceptions, and considering the older age group of feedlot animals, the spectrum of diseases commonly affecting cattle and sheep in confined feeding operations (feedlots) does not differ greatly from those observed in cow-calf or stocker businesses. Special circumstances in the feedlot do, however, modulate the frequency, magnitude, and economic impact of these diseases (Table 1).  Various factors act in concert to seriously impact the incidence and severity of diseases in the feedlot setting.

Fig. 1: Data from incidence of disease among cattle in US feedlots.  Respiratory diseases are far and away the most important sources of disease and loss

As you are aware, recently weaned calves and lambs are stressed.  They are more susceptible to infectious disease. Calves and lambs entering feedlots can be unvaccinated or have questionable natural and acquired immunity. The source of animals entering a feedlot can also effect the incidence of diseases that occurs. Animals entering the feedlot from one source, i.e. directly from a ranch, may be imnnunologically naïve to many of the infectious diseases they encounter in confinement operations. Alternatively, other animals are purchased from order buyers or through sale barns with recent exposure to a variety of diseases immediately prior to arrival at the feedlot. Another factor to consider with regard to the source of animals is their origin; in other words,  climatic and other conditions to which animals were acclimated may be differ markedly from what they are exposed to in the feedlot.  Transport stress has well recognized effects on animals with regard to susceptibility to infectious disease. Already hinted at is the effect of commingling animals either at the feedlot or at sale barns and order buyer facilities. This exposes some animals to a multitude of infectious diseases to which their immune systems have not been specifically primed or to which their immunity may have waned. Lastly, there are dietary concerns that can contribute to a whole host of problems. Animals arriving at a feedyard have generally not received adequate or plentiful water and food prior to and during transport. The animals are exposed to a potentially new environment where drinking from water troughs and eating from feed bunks are new experiences, further contributing to water and feed concerns. Cost of feed, weight gain, and marketing are the most important economic factors driving the feedlot industry. From a nutritional perspective, these animals are pushed to the maximum using concentrated, high carbohydrate-based rations to effect efficient feed conversion and marketing within a customary time frame. Although effective from an economic standpoint, such rations can contribute to or cause serious digestive disturbances if there are interruptions in the delivery of feed to the animals.

Respiratory diseases

Respiratory disease is the most important cause of sickness (morbidity), death (mortality) and of or chronic, poor-doing animals in feedlots.

Bovine respiratory disease (BRD) complex/shipping fever: Various predisposing factors contribute to this disease.  These include commingling cattle from multiple sources, altered immune status, and other stressors. Feedlots are often dusty environments with the air laden with organic dusts including mold spores, plants particles, and endotoxins. This dusty environment can hinder some of the protective mechanisms existing in the respiratory system, and allow infection by various microorganisms to gain a foothold. Shipping fever is a complex disease, involving the interactions of these predisposing factors with superimposed infection by a variety of viral and bacterial pathogens ultimately leading to pneumonia. As this is covered elsewhere in the course, the various viral and bacterial pathogens are listed here for reinforcement (Table 2). Some of the more severe respiratory disease ‘wrecks’ are encountered when naïve calves of ranch origin are introduced into the feedlot and exposed to these pathogens when commingled with calves that originated in sale barns or were grouped by order buyers already incubating an infection or with ‘early stage’ pneumonia. Very young, lightweight cattle, cattle not acclimated to weather extremes, and animals transported long distances are at increased risk.   As you might expect, there is a distinct seasonality to respiratory disease - it tends to peak in the fall and winter months.

Percentage death loss in sentinel feedlots by cause.  Note that respiratory disease is more important that all others in every month.  It peaks in Sept - Nov. USDA Animal Health Report 2006

An animal with pneumonia will be uncomfortable (as would you), will drooped ears, a dull eye, and gaunt.  Other signs are being off food, some (or a lot of) nasal discharge (pus or mucus), a high rate of ventillation, coughing (if it's moist - it's pneumonia), and fever (>104.0 F).

Atypical interstitial pneumonia/acute bovine pulmonary edema and emphysema: In range or pastured cattle, this disease is most commonly associated with movement of cattle from dry or dormant pastures to pastures with active lush growth. The disorder is also associated with ingestion of some plants or mold-contaminated plants. The cause is the high tryptophan levels with conversion to 3-methylindole, a pneumotoxic (= toxic to tissues of the lung) metabolite. In feedlot cattle this disease is fairly common, but its incidence is sporadic. There is some seasonality, with problems occurring in spring, and late summer-fall. The disease may be associated with rations containing high levels of tryptophan but this does not seem to be the cause or sole explanation in some instances. Other causes, all difficult to prove and speculative, include allergic reactions to molds or other organic antigens, reactions to lungworms (Dictyocaulus spp.), and inhalation of dust-laden air. In some instances infection with and/or vaccination for respiratory syncytial virus have been incriminated.  This seems to not uncommon in feedlot situations.

DIGESTIVE SYSTEM DISORDERS

Diseases affecting the digestive system are second only to respiratory disease as a cause of morbidity and mortality. 

Digestive diseases due to infectious/septic/parasitic causes: With the exception of diseases associated with neonatal scours, the primary infectious diseases affecting the digestive system of feedlot cattle are little different from diseases found in other husbandry situations. Most of these are covered elsewhere lectures and are included here in tabular form (Table 3).

Physical diseases: Diseases due to organ misplacements, torsion, or volvulus of the tubular digestive tract are uncommon in feedlot cattle and will not be covered here. Another, largely physical disorder, is ruminal tympany ("bloat"). Rumen fermentation produces gas that, even with maximum gas production, can be expelled via eructation preventing accumulation and rumen distension. There are three classes or types of bloat. Frothy bloat occurs when the gas produced by fermentation is trapped within the mass of ingesta, preventing accumulation of free gas in the dorsal or uppermost part of the rumen or gas cap. This type of bloat occurs when cattle graze lush legumes or winter wheat pastures and also is seen with ingestion of highly concentrated rations typically used in feedlots. The second type of bloat is free-gas bloat. One of the more common causes of free gas bloat is exposure to higher levels of highly concentrated, readily fermentable carbohydrate rations to which the animals are not accustomed. This results in increased acidity of the rumen, ultimately resulting in decreased rumen motility and contractions requisite for eructation and free gas accumulates. The third type of bloat, obstructive bloat, results from the inability to eructate ruminal gases due to obstruction of the esophagus (uncommon in feedlots) or to mainly left lateral recumbency where rumen ingesta covers the cardia of the rumen.

Metabolic disease: The primary metabolic disease affecting the digestive system is ruminal acidosis. Cattle adjust to high levels of readily fermentable carbohydrates provided it this is done gradually so the rumen can acclimate. When exposed to concentrate rations suddenly, acidosis occurs. Acidosis also occurs in situations where the supply of feed is interrupted and cattle over-consume. Normal rumen pH of cattle on concentrate rations is typically 5.0 to 5.5.  A pH of 5.0 considered borderline - the cutoff for diagnostic purposes. It should be remembered that it is not only the absolute pH of the rumen content, but the speed at which the acidosis occurs that dictates the outcome. Acidosis can have profound localized (in the rumen) as well as systemic effects. Localized effects include chemical rumenitis (inflammation of rumen) due to the caustic affects of the acidic environment, rumen atony (= decreased motility), death of the normal microflora, and overgrowth of other microbes. With chemical rumenitis, loss of the normal epithelial protective barrier, and overgrowth of abnormal flora, a more severe rumenitis can develop due to organisms such as Fusobacterium necrophorum, and occasionally fungi. These infections can spread via the vasculature to other tissues, commonly the liver, with formation of liver abscesses resulting in further morbidity. Systemic effects can occur from dehydration due to loss of body fluid into the rumen, the death of normal ruminal microflora, overgrowth of abnormal microflora (see discussion of polioencephalomalacia), due to endotoxin release and systemic absorption from Gram-negative bacteria killed in the acidic environment, or to the systemic effects of the acidosis per se. 

Cattle with rumenitis appear drunk.  They will walk stiffly, have diarrhea, and pass foul feces.  If it's bad, animals become dehydrated.

Treatment of acidosis involves holding off on concentrates, feeding grass hay for 1 - 2 days, use of alkalizing agents ("antacids")(e.g., Carmilax boluses - Pfizer) to counteract acidity, laxatives such as mineral oil, antibiotics if it is not looking good, and electrolytes if the dehydration (due to diarrhea) is bad.

DISEASES OF THE CARDIOVASCULAR SYSTEM IN FEEDLOT CATTLE

Diseases of the cardiovascular system are not common in feedlot cattle but occur with sufficient frequency to be a concern.

Myocarditis, vasculitis (inflammation of the heart, blood vessels):  The heart and major blood vessels can be involved with certain viral diseases as part of the general picture of the viral infection but these are not particularly important in the feedlot situation. One viral disease, malignant catarrhal fever, is predominantly a disease of blood vessels, arteries and smaller arterioles, involvement of which leads to damage in a variety of organs and tissues.   The disease is due to contact between cattle and sheep; sheep shed the causative virus from their nasal passages.  While it does nothing to the sheep, infection of cattle can cause a severe systemic illness that most commonly manifests as heavy discharges of muco-pus from the nose and eyes, ending in death.  Two bacterial diseases are of concern. Haemophilis somnus can infect the heart, leading to focal necrosis (death of tissue) and myocarditis. The papillary muscles of the left ventricle of the heart are commonly involved. Death is usually sudden in these animals. One other bacterial disease affecting the heart is ‘visceral’ blackleg caused by Clostridium chauvoei. Acute myocarditis with necrosis is present and inflammation may also involve the pericardium and/or the membranous coverings of the lung (pleural) resulting in pericarditis and pleuritis. Similar involvement of the membranous coverings of the abdominal cavity (peritoneum) can also occur. Death is usually sudden. Traumatic reticulopericarditis (hardware disease) can also be observed in feedlots. Inflammation on the surface of the heart (epicardium) and pericardium resulting in epicarditis and pericarditis is seen occasionally and Pasteurella multocida or Mannhemia hemolytica can be cultured from these cases.

WSU/ARS web site on MCF

Myocardial degeneration, cardiomyopathy: Nutritional causes of cardiac myodegeneration include vitamin E/selenium deficiency and, rarely, copper deficiency.  These are typically deficiency states that are present at the time the cattle enter the feedlot and the incidence in feedlots generally parallels that in other types of husbandry operations. Toxic causes of myodegeneration are occasionally incriminated in the feedlot. These include toxicities caused by inadequate or faulty mixing of ionophores such as rumensin in the feedlot ration allowing some animals to receive toxic amounts. Gossypol, a toxin present in cottonseed used to formulate feedlot rations in some areas of the country, has also been incriminated, mainly in very young animals entering a feedlot and most commonly in Holsteins. Congestive heart failure, usually right-sided, with enlargement and dilation of the heart also occurs in feedlots and many cases are of undetermined cause. Some, but certainly not all, animals have had chronic pneumonia with scarring. The scar tissue potentially leads to increased vascular resistance and increased intravascular pressure (pulmonary hypertension) resulting in right-sided cardiac failure, a syndrome known as cor pulmonale. This is similar to the mechanism of heart failure with high altitude (brisket) disease.

DISEASES OF THE NERVOUS SYSTEM IN FEEDLOT CATTLE

Disease of the nervous system in feedlot cattle occur with some frequency and can have an economic impact.

Infectious/inflammatory disease of the nervous system: Viral infections of the nervous system are uncommon in feedlots. Certain herpesviruses, such as bovine herpesvirus-5, are neurotropic (target the nervous system).   Due to the potentially long incubation period, rabies is occasionally encountered in feedlots. The primary bacterial disease affecting the nervous system in feedlot cattle is thrombotic meningoencephalitis (TME or TEME) caused by Haemophilus somnus. Meningoencephalitis (inflammation of the brain and meninges) due to this organism can occasionally be observed along with infection in other organs but this is not typically the case. Brain abscesses occasionally occur in feedlot cattle. These result from penetrating injuries or from extension of inflammation in adjacent tissues such as the inner ear. One type of abscess, involving the cavity surrounding the pituitary gland (pituitary fossa abscess) may extend into the pituitary stalk and then into the ventricular system of the brain. The origin of pituitary fossa abscesses in undetermined but the lesion may reflect further extension of an infection involving the nasal passages or sinuses. Arcanobacterium pyogenes and Pasteurella multocida may be cultured from these abscesses.

Metabolic diseases of the nervous system: Probably the single most important disease affecting the nervous system of feedlot cattle is polioencephalomalacia ("PEM"). This disease is covered in other lectures and is mentioned here only as it pertains to feedlots. Although a variety of factors have been incriminated in the genesis of the disorder, ruminal acidosis in feedlot cattle seems to be one of the more common, if not most common, predisposing factoring in the industry. With acidosis, it is proposed that there is a die off of thiamine producing bacteria in the rumen and/or overgrowth of bacteria that degrade thiamine (thiaminase-producing bacteria). Formulation of rations containing excess sulfur and/or high sulfur levels in the drinkingwater may also be predisposing factors. ‘Nervous’ coccidiosis is also a disorder that may be observed in feedlot cattle. This neurologic disease is commonly, but not invariably, associated with severe coccidiosis, the parasites being demonstrable on fecal flotation or in the large bowel accompanied by marked edematous (increased fluid) thickening of the bowel wall and associated mesentery. The cause of the neurologic disturbance in this syndrome is unknown. Examination of the brain grossly or microscopically does not reveal definitive lesions, so veterinarians make the diagnosis based on clinical signs and the absence of other explanations for neurological signs.

DISEASES OF THE URINARY SYSTEM IN FEEDLOT CATTLE

One disease, leptospirosis, is occasionally seen in feedlots and is caused by various serovars of Leptospira interrogans, mainly hardjo type hardjo-bovis and pomona and less commonly other serovars. After infection, there is a generalized bacteremia (presence of spirochetes in blood), at times resulting in acute destruction of red blood cells leading to anemia and hemoglobinuria (presence of hemoglobin from lysed red blood cells in urine). During the subacute and chronic stages, the organisms localize and infect the kidneys, shedding leptospires in the urine. Additional manifestations of the disease that can be seen depending on the animal are abortions, stillbirth, mastitis, and decreased milk production. Pyelonephritis, an ascending bacterial infection of the kidney, may be occasionally seen in feedlot cattle but is rare in sheep. Mortality associated directly with the infection is uncommon but the lesions of pyelonephritis may be encountered as an incidental finding in animals dead from other causes. Urolithiasis is the formation of calculi or stones in the urinary tract.  This is a problem in male feedlot ruminants, although it can also occur in steers on pastures. The calculi lodge in the urethra (most common)(see below) or in other areas of the urinary tract, causing trauma to these structures and leading to urinary obstruction.  Affected steers have abdominal pain (colic).  Trauma and obstruction can further result in rupture of the urinary bladder or urethra leading to uroperitoneum (= free urine in the abdomen) or leakage of urine into the subcutaneous tissues of the perineum and ventral abdomen, a syndrome known as ‘water belly’. As you recall, feedlot rations are grain-based. These have a high phosphorus content.  As a result, in feedlots, most problems are due to phosphatic calculi. In western areas of the country, soils and grasses can have high silica.  In these pasture situations, silica can cause urolithiasis.

Urolith (arrow) in the penis of a calf.  The material is hard and gritty.	Inner lining of the bladder from the same calf as that shown on the left.  The bladder is intensely hemorrhagic (red) as a result of the blockage.  This bladder ruptured, killing the calf

 

MISCELLANEOUS DISEASES AFFECTING VARIED ORGAN SYSTEMS

Other diseases affecting a variety of organ systems can be found in feedlot cattle (and sheep) and these generally mirror diseases found in other types of animal husbandry operations. Lameness due to footrot, abscesses, and degeneration and inflammation of joints and tendons (arthritis, synovitis, tenosynovitis, etc) are relatively common problems that occur in individual animals. One syndrome of lameness and swelling of multiple joints and periarticular (soft tissues around joints) tissues that can affect multiple animals is attributed to Mycoplasma bovis. By the time the problem is recognized clinically, the disease is chronic and the illness is generally refractory to treatment.  Buller steer syndrome is a behavioral disorder in which some steers ('bullers') are repeatedly mounted and ridden by penmates ('riders').  There are two types of buller - the true buller, who will stand to be mounted and acts like a heifer, and social bullers, who are low on the totem poll and will try to avoid this, yet can't.  The syndrome is important because bullers are susceptible to disease physical injury, muscle damage, and occasionally broken bones.  It was ranked as one of the three most common health problems in cattle feedlots with 2.2% of all cattle affected in the 1999 NAHMS survey (see Fig 1).  Bullers tend to arise shortly after entry into the feedlot, when animals are regrouped, and during prolonged hot spells.  The first two observations suggest one component is the establishment of social hierarchies.  Hormonal implants may aggravate the problem by causing steers to be more aggressive and bull-like in behavior.  Control is by forming pens with as few groups as possible, by reducing the number of animals per pen, and by implanting on arrival rather than later   Some feedlots in the United States limit the number of steers in a pen to no more than 240 head/pen to minimize incidence.  Frequent pen checks are helpful to ensure rapid identification and removal of buller steers.   Some feedlots with high rates of this disorderconstruct buller guards, under which affected animals can find protection.  The most effective treatment of bullers calls for prompt removal of animals being ridden and placing them in buller pens.  Buller syndrome has been banned in Kansas and much of the south, as well as Iran.  The only problem with this is that it does not work.

DISEASES OF FEEDLOT SHEEP

In contrast to cattle, the knowledge base concerning diseases of feedlot sheep is limited.  As a general rule, the same or similar diseases affecting cattle also occur in feedlot in sheep. Respiratory diseases in sheep are much less common.  Multiple viral infections that are typical predisposing or primary factors in shipping fever of cattle are not well recognized in sheep. Viruses that have been implicated include parainfluenza type 3 virus (PI3) and respiratory syncytial virus (RSV). The virus related to the human immunodeficiency virus and that causes ovine progressive pneumonia is not common, due to the younger age of feedlot sheep. Bacterial pathogens such as Pasteurella multocida, Mannheimia hemolytica, and mycoplasma (M. ovipneumoniae) are the primary causes of morbidity. With the exception of viral diseases affecting the digestive system, other diseases in sheep are similar to those in cattle and include bacterial infections such as salmonellosis and parasitism (nematodes, cestodes, and coccidia). Of major importance are digestive disorders associated with feeding concentrate, grain-based rations. Acidosis itself can be a major cause of morbidity and mortality. Important complications include rumenitis due to the caustic effect of the low pH, polioencephalomalacia, and enterotoxemia due to Cl. perfringens type C or, most commonly, type D (overeating disease, pulpy kidney disease). This disease is due to intestinal overgrowth of strains of Cl. perfringens producing the epsilon toxin. The disease can be seen in calves but is most common in sheep. Some animals, especially young lambs and calves, may be found dead. Older animals, mainly sheep, may develop a more subacute form of the disease. In the subacute form, signs of abdominal pain and diarrhea may be present. Some animals develop a neurologic syndrome termed focal symmetrical encephalomalacia (encephalo = brain; malacia = softening; FSE) due to the action of epsilon toxin on blood vessels leading to increased vascular permeability.

Dr. Don Montgomery

Updated: 01/29/2010