Stocker Cattle Health Considerations

Bob L. Larson, DVM, PhD, ACT

As cattle enter a backgrounding/stocker facility, the group can be assigned one of three risk-categories. (1) Low risk cattle are yearlings that have previously been exposed to the pathogens (germs) that cause pneumonia, either through an effective vaccination program or by natural exposure. (2) High-risk unexposed cattle are ranch-fresh, weaned calves that have naïve immune systems because they have been isolated from other cattle (and their germs). These calves may or may-not have had a long truck ride to the stocker facility. (3) High-risk exposed cattle are recently weaned calves that have been commingled in an auction or order-buyer facility with other recently weaned calves and then trucked a long distance to the stocker facility. These calves have been exposed to most if not all of the pathogens that cause respiratory disease prior to arrival at your farm. Any calves with greater than 5% shrink have fluid loss from tissues and are at a high-risk for disease.

At arrival, calves should be placed in drylots with free access to good-quality grass hay and fresh water and allowed to rest overnight. Drylots offer several advantages over grass traps immediately after arrival. Calves kept in drylots have lower illness and death rates, improved gains, and lower labor costs. Traps allow calves too much room to walk fences, causing more physical stress and allowing them to stray too far from feedbunks and water sources. Confining calves in drylots or grass traps for up to 3 weeks before turning them out to pasture is often necessary for allowing recovery from stress-related disease in some groups of received cattle. Calves are not usually very competitive at the feedbunk, so a minimum of 22 to 26 inches of bunk space per animal should be provided. The bunks should be kept clean and old feed removed daily. One to two pounds per head of a palatable protein pellet should be offered in the feedbunk upon arrival. Clean water tanks with water running from a hydrant will often encourage calves to drink because many are not accustomed to drinking from automatic waterers. For highly stressed calves, keeping arrival pen size to 50 animals or less is ideal.

Depending on the risk category of the calves at arrival, timing of normal processing activities may be altered.  Arrival activities such as dehorning (or horn tipping), castration, and implanting may be delayed in high-risk cattle until the risk of respiratory and other disease decrease. De-worming and vaccination against viral diseases will proceed shortly after arrival.

Arrival Processing

            Proper handling and management of cattle during processing is essential to minimize stress, to reduce the risk of injury and to detect sick cattle as soon as possible. Processing should not be delayed for more than 24 to 36 hours after arrival. Longer delays result in higher rates of illness and do not take full advantage of the protection offered by vaccines or preventive medications. Each day that processing is delayed results in a 1% increase in rate of illness. Body temperatures should be taken as the cattle are processed if they have been rested overnight. Body temperatures of cattle just unloaded from the truck are not reliable indicators of illness. It is important to process in small groups, so no animal is out of its pen for more than 30 minutes. Process early in the morning to avoid higher environmental temperatures later in the day and to avoid artificially elevated body temperatures taken in the afternoon. An electronic thermometer is essential. Calves with a body temperature of 104° F or greater or showing other signs of illness should be separated from the group and kept in a hospital pen where they will receive a treatment program as outlined by the veterinarian working with you. Even though body temperature can be a valuable indicator of illness, too much reliance can be placed on rectal temperature. The appearance and history of the calves should be considered in deciding whether the calf is actually ill. Once sick animals identified at arrival have been separated, and the cattle are accustomed to the bunk and waterers, turn the healthy animals onto grass traps to allow more space and comfort. Grass traps that allow four animals per acre, for the short receiving period, usually maintain continuous turf and can be sustained for long periods.

            It is tempting to use all available vaccines and bacterins to minimize disease. But, many calves entering backgrounding or stocker operations are highly stressed and they may be able to respond to only a limited number of antigens. The presence of colostrum-derived antibodies may also limit immunization against some diseases. Therefore the veterinarian must consider the following when outlining a vaccination program: risk of disease, stress level of the calves, age of calves and presence of colostral antibodies, stress induced by vaccination, efficacy of the vaccine, previous vaccination history, and the time of onset of disease after arrival. Vaccination programs should be tailored to meet the needs of calves of various ages, levels of stress, and origins. The benefit of vaccination upon arrival is uncertain in some cases. Using bacterins or killed virus vaccines to provide protective immunity when given on arrival is usually not very successful. However, it has been demonstrated that modified-live viral vaccines will likely provide protective immunity within days. The respiratory diseases with effective vaccines available include IBR, BVD and PI3. Pasturella vaccines are effective at decreasing respiratory disease in certain situations.

Other Arrival Procedures

            Growing, young cattle are susceptible to the negative health and production effects of internal parasites (worms) and external parasites (lice, grubs, mange, flies). Treating cattle at arrival with a de-wormer is almost always recommended. A moderate to heavy parasite burden decreases gain and efficiency and has negative effects on the immune system. Products that control type II ostertagiosis are recommended (Class III anthelmintics), especially in cattle originating in the southeastern United States after long dry periods or in winter. In cattle where liver flukes are confirmed or suspected, a product that will control these parasites is recommended. External parasite control is important for optimum gain and immune function, but organophosphates should be avoided during the first three weeks after arrival. Pyrethroids are often used in stressed cattle.

Implants containing anabolic steroids to enhance growth are very profitable to use if the cattle are going to be owned long enough to capture the added weight gain. Cattle that are implanted have better gain and feed conversion compared to non-implanted controls. Some factors that influence the choice of implants are: age and sex of the cattle, ease of administration, implant cost, and comparative performance of implants in the areas of growth, feed efficiency, and carcass traits. Implants should be replaced every 70 to 120 days (depending on the implant) resulting in a 20 to 25 pound advantage per implant. To ensure that implants will perform optimally, the needle should be sharp and clean, the animal’s head movement should be controlled, and the implant should be placed properly in the middle 1/3 of the ear.

Arrival Nutrition

            Newly received stressed calves have special nutritional problems. Inadequate or stress-inducing nutrition practices compound health problems. Stressed animals often eat too little for nutrient levels that aid in recovery to be achieved. With many feeds, animals initially eat too little and later eat too much, which can lead to digestive upset and other health problems. Feed intake is low, ranging from .5 to 1.5 per cent of their body weight on a dry matter basis during the first week. Feed intake increases through the third week and reaches a plateau during the forth week. It is essential that a palatable ration is offered, and nutrient densities are raised when feed intake is low. Pounds of nutrients consumed during the receiving period are of greater importance than are percentages of nutrients in rations.

            The use of silage in receiving rations is generally associated with higher illness and mortality rates. Silage should not be included in receiving rations during the first 2 weeks after arrival. Silage is generally low in protein; therefore, once it is included in the diet, calves should be supplemented with natural protein for meeting daily requirements.

            Alfalfa hay, although palatable and of good nutrient value, often causes bloat and contributes to loose stools. Moldy or poor-quality hay decreases consumption and should be avoided.

            Concentrate levels above 55% during the receiving period are often accompanied by higher levels of illness and higher medication costs; however, average daily gain and feed efficiency will be improved. Feeding good-quality, long-stem hay, such as prairie or oat hay, results in the lowest illness and mortality rates. A good balance of health, average daily gain, and feed efficiency is obtained when a ration approximating 72% concentrate is fed. Limit-feeding a concentrate ration for obtaining a calculated average daily gain and cost of gain offers advantages of controlling weight gains to achieve desired weights for future grazing or to take advantage of more favorable markets. Feeding long-stem grass hay free-choice, with up to 2 pounds/day of a palatable 38 to 40% natural protein pellet results in excellent health performance, and gains of 1 to 2 pounds/day can be expected during a 28-day receiving period. Grinding the hay and including it directly into the entire ration is preferred. Calves perform better if a completely mixed diet is fed.

            Crude protein (CP) content in the starter diet should also be relatively high. The starter or weaning ration should contain at least 14% crude protein on a dry matter basis. Calves are not capable of utilizing urea or other nonprotein nitrogen sources very efficiently. In addition, as urea decomposes in the feedbunk it gives off an ammonia odor. The smell of ammonia in the bunk may reduce intake.

            Cole and Hutcheson (1990) reported that increasing the crude protein concentration of receiving diets from 12 to 16% resulted in increased average daily gains during the first 14 d in the feedlot. One explanation for these results is that as an animal's Dry Matter Intake (DMI) decreases, the crude protein content of the diet must be increased to meet that animal's requirement for grams of protein. The results indicate that crude protein requirement of market-transport-stressed feeder calves is similar to requirements of nonstressed calves; however, the protein concentration of the diet of stressed calves may need to be increased when feed intakes are low.

            Fluharty and Loerch (1995) looked at protein concentration and protein source for diets of newly arrived feedlot steers and found that average daily gain and feed efficiency increased with increasing (11, 14, 17, 20, 23, 26%) crude protein concentration during the first week after arrival.

            Calcium content of the starter diet should be .67%, phosphorus content should be .45% and magnesium content should be .25% of dry matter. Potassium content should be at least .80%. Some studies have suggested that while .80% potassium was adequate for unstressed cattle, cattle that suffered excessive shrink (>5%) and that were highly stressed may require up to 1.4% potassium in the diet. Providing adequate potassium will aid cattle in recovering the weight lost as shrink more quickly. 

            Forages are generally good sources of calcium and potassium. Grains are poor sources of calcium and potassium and a good source of phosphorus. Since relatively high concentrate diets should be used, mineral supplements fed to starter calves should be relatively high in calcium and potassium. Once the cattle are started on feed and worked to a growing program, the mineral supplement needs of the cattle will change, particularly if more forage is used in the growing program.

            Cattle require small amounts of trace minerals. Zinc, copper, selenium and iron have been shown to play an important role in immune response. Under most circumstances, providing trace mineral salt to the cattle at the rate of .5% of dry matter will meet their trace mineral requirements. Mixing the trace mineral salt in with the supplement is preferred over providing it free choice. Calves from some origins may be selenium, zinc, or copper deficient. A premix should be developed to compensate for these deficiencies in calves from particular origins. Vitamin A content of the ration should be relatively high. Provide about 2500 IU of vitamin A per pound of ration dry matter. Vitamin A injections (1 million units) should be given to calves that originate from vitamin A-deficient areas. The B complex vitamins are generally synthesized in sufficient quantities in the rumen of cattle and usually do not need to be provided. However, if the cattle have been off feed for some time, supplemental B vitamins (600 mg niacin, 200 mg thiamin and 750 mg choline per head) may be beneficial. Some research has suggested that vitamin E supplementation in the receiving ration at 400 IU per head per day improves health and performance of newly received stressed calves. Further work may or may not support this finding.

            Ionophores should be included in stocker supplements because they increase feed efficiency and average daily gain, help prevent digestive upset, and control coccidiosis. Metabolizable and net energy values of feeds are increased when ionophores are consumed. Ionophore use in conjunction with high roughage diets (pasture, hay, or silage) results in the same consumption but increased rate of gain because of improved efficiency of feed utilization. Ionophore use in conjunction with high-energy, feedlot-type diets results in decreased feed consumption but similar rate of gain - once again due to improved efficiency of feed utilization. In numerous trials utilizing both heifers and steers and grazing various forage types (native grass, bermudagrass, fescue, crop residue, winter wheat) fed a small amount of supplement (1-2 lbs. daily) with or without ionophores, average daily gain was improved 8-45% (0.12-0.22 lbs./day) with ionophores. In addition to their effects on gain and efficiency, ionophore supplementation is effective for the prevention of acute bovine pulmonary emphysema and edema (ABPEE) and bloat when cattle graze lush pasture.

Bovine Respiratory Disease (BRD) or Pneumonia

Bovine Respiratory Disease (BRD) or pneumonia is the primary cause of sickness and death in a backgrounding or stocker operation. Edwards (1996) reports that 65 to 80% of morbidity within a feeding period occurs in the first 45 days, and 67 to 82% of the total morbidity was due to respiratory disease. Mortality rates ranged from 0.57 to 1.07% of all cattle received with respiratory disease accounting for 46 to 67% of deaths. Vogel and Parrott (1994) used data collected from January 1990 to May 1993 and reported that the mean monthly mortality rate due to respiratory disease for the feedlots where data was collected was 0.128% (1.28 respiratory mortalities per month per 1,000 head on feed), with 44.1% of all mortalities due to respiratory disease.

A number of viruses and bacteria have been associated with BRD. In healthy cattle, exposure to any one of these pathogens would not be likely to cause disease. Interactions among the pathogens and depression of the immune system due to environmental, nutritional, or management stress seem to be necessary to cause BRD.

Environmental stressors include heat or cold stress, dust, and fumes toxic to the lining of the respiratory tract. Dehydration, exhaustion, rough handling, and mixing cattle into new social groups are examples of management stressors. Failure to provide adequate water, energy, protein, or minerals causes nutritional stress.

Viral infection usually proceeds bacterial pneumonia, though it is not required for BRD. Infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), parainfluenza virus (PI3), and bovine respiratory syncytial virus (BRSV) are known to cause damage to the epithelial lining of the respiratory tract which causes inflammation, damage to the pulmonary clearance mechanism, and allows suitable sites for bacterial replication. The damage is not confined to the upper respiratory tract, but extends to the lung bronchi and alveoli. Modified live viral vaccines have been shown to be protective against experimentally induced bacterial pneumonia by preventing sufficient viral damage to the tract to allow bacterial colonization.

In general, bacteria do not serve as primary pathogens of BRD in healthy, unstressed cattle. Damage to the epithelial lining of the lung and immune suppression is required for bacteria to colonize the lung and cause pneumonia. Pasteurella haemolytica is the most commonly isolated bacterial agent in fatal cases of BRD. P. multocida is also isolated from BRD cases. Both of these bacteria normally reside in the upper respiratory tract and are able to invade the lung only if defense mechanisms breakdown. Clinical signs of BRD usually develop within 14 days following environmental or management stressors. Haemophilus somnus has been reported to cause fatal BRD in the colder climates of North America (Canada). Controversy exists about the role of H. somnus in BRD in moderate climates. Modern subunit Pasteurella vaccines are thought to be effective if given well in advance of stressors that lead to BRD. Modern vaccines for H. somnus have not been sufficiently evaluated, however, the available H. somnus bacterins have limited or no efficacy for preventing BRD.

Finding Sick Cattle

Early detection of BRD cases is important in order to increase the likelihood that treatment will be effective. If BRD cases are identified early, almost any modern treatment plan (antibiotic) is likely to succeed; and if BRD cases are not detected until late in the disease course, all treatment plans are likely to fail. The result of late detection of BRD cases is an increase in the number of re-pulls, chronics, railers, and deads.

Feed and/or hay should be present in the bunk prior to the cattle being observed, this allows producers to identify the cattle that aren’t coming up to the bunk. Producers should observe and listen for a period of time before he/she enters the cattle pen, so that undisturbed activity and coughing can be evaluated. Once a producer enters the pen, he/she should try to determine if any animal looks or acts sick.

Sick cattle may have the appearance of lack of rumen fill, nasal discharge, or increased respiratory rate and/or difficulty. Rumen fill is important to evaluate because sick cattle often do not eat, and cattle that do not eat often become sick. Sick cattle may also “tank-up” on water but refuse to eat hay or grain. These calves are gaunt high in the flank, but have a pendulous belly that swings from side to side. Rumen fill is more difficult to evaluate in cattle that have been on feed for awhile because they are slower to go off of feed when they get sick and the increased fat cover obscures the extent of “gauntness”. Thick (opaque) nasal discharge is a common indication of respiratory disease. Nasal discharge on the back of the feed bunk indicates that at least one calf in the pen is likely affected with BRD, and opaque nasal discharge visible on a calf is good evidence that he needs to be treated for BRD. Clear nasal discharge is not an indication of BRD.

            Sick animals may act differently than their healthy pen-mates as displayed by a decreased interest in their surroundings, lowered head and ear position, and reluctance to move or when they move they move without “purpose”. When the cattle are slowly moved around the pen, sick cattle often filter to the back of the group or even begin to lag behind or stop walking altogether. Mild to moderately affected cattle may improve their attitude when being moved around the pen with the group, so the cattle need to be observed while standing quietly as well as while on the move.

            Cattle that often grab the attention of producers looking for sick calves include calves that have been treated previously, animals that have less fat-cover than their pen-mates, and cattle that are a different breed or color than the majority of the pen. These cattle may not be sick at all, they just attract attention because they have a different appearance or are easily recognized.

            Weather greatly impacts the number of cattle that become sick with BRD. The number of cattle needing treatment for pneumonia typically increases 2 to 3 days after they get wet. Any environmental extreme will increase the incidence of sickness, but becoming wet will cause the greatest and most consistent increase.

            Some producers utilize mass-medication at arrival or a few days later with injectable, long-acting antibiotics for high-risk cattle in an effort to reduce the number and severity of sick animals. This strategy is cost-effective in some situations. If fresh cattle are received, and if there is sufficient skilled labor available, this practice may not be cost-effective. When there is a shortage of labor or when employees are not highly skilled at detecting sick cattle early, mass medication may be a useful management tool. It is of greatest benefit when it is used on sale-barn cattle assembled from several sources or on extremely stressed calves. In many instances, one mass medication treatment will be as effective as a 3-day program. Timing is important because mass medication too far in advance of the onset of illness or too late will be ineffective.  The selection of antimicrobials should be based on previous culture and sensitivity data or on clinical response.

            Galyean et al (1995) conducted three trials and found that tilmicosin phospahte (Micotil) mass treatment of newly received, stressed beef cattle decreased (P<.01) the percentage of calves treated for symptoms of respiratory disease in all three trials. Daily gains and DM intake were numerically greater with Micotil mass medication in trial 1, were significantly greater in trial 3, and not different in trial 2.

Treating Calves with Respiratory Disease

            Once cattle are identified as needing treatment for respiratory disease, they are moved to a treatment area and treated with at least a three-day protocol of antibiotics. The antibiotics used should reach effective concentrations in diseased lung, and be effective against the bacterial organism that is causing pneumonia. Several very good antibiotic choices exist and the final determination of which product to use is based on how the antibiotic distributes itself in the calf’s body, laboratory determination of susceptibility of the bacterial organisms to the antibiotic, and previous clinical response on that particular farm. Cattle that are dehydrated are often given oral fluids with a stomach tube in addition to antibiotic therapy. Sick cattle are usually placed on a higher roughage diet than the home pen cattle. The diet is routinely 60 to 70% concentrate with at least a 15% all natural protein level. Fresh hay and water are always available in the sick-pen. Once calves are determined to have recovered, they are placed on increasingly higher concentrate diets to prepare them to return to their home pen. Cattle that don’t respond to therapy with improved appetite, weight gain, and respiratory function are determined to be “non-responders” or “chronics” and often sold as “realizers”. Cattle that respond to treatment and returned to their home pen only to be pulled out of the pen at a later date for a second case of respiratory disease are called “re-pulls”. A high incidence of chronics indicates that the cattle were not identified early in the disease process. A high incidence of re-pulls indicates that either the cattle were not evaluated properly at the end of the initial treatment period, or the initial treatment was not adequately effective.

            When illness within a pen suddenly increases or when feed intake drops, revaccination with a modified live IBR vaccine will generally reduce morbidity. An antibiotic administered concurrently aids in reducing rate of illness further.

Definitions of interest in stocker operations:

Morbidity rate – Number of animals pulled for treatment, divided by the number of animals in the received group.

Mortality rate – Number of animals in the received group that died, divided by the number of animals in the received group.

Case fatality rate (CFR) – Number of animals in the received group that died, divided by the number of animals treated.

Repeat rate – Number of animals requiring a second treatment for the same disease occurrence because their clinical appearance markedly deteriorated during the 72 hours following initial diagnosis and treatment (i.e. treatment failures), divided by the total number of treated calves.

Repull (Relapse) rate – Number of animals that are considered treatment successes (i.e. recover by 72 hours after initial treatment) that are pulled from the pen (require a second medication) later in the feeding period, divided by the total number of treated calves.

Chronic rate – Number of animals that did not respond to two treatments, divided by the total number of treated calves.

Other Health Problems in Stocker Cattle

Bloat

            Stocker cattle can have two types of bloat, free gas bloat and frothy bloat. Frothy bloat can be either pasture bloat associated with legume forages or wheat pasture, or grain bloat. Alfalfa, red clover, and white clover are the most likely legumes to cause pasture bloat. Arrowleaf clover, birdsfoot trefoil, cicer milkveetch, and sainfoin are much less likely to cause a problem. The most important plant factor causing bloat is soluble protein. As the plant matures, soluble protein levels decrease, thereby decreasing risk. Some animals have increased susceptibility to bloat that appears to be determined genetically. Researchers have found that the prevalence of bloat is increased in the offspring of certain bulls. In addition, breed differences are evident. Holsteins are the most susceptible and Brahma-type cattle are unlikely to bloat.

Death can be rapid in frothy bloat cases due to asphyxiation because of pressure on the diaphragm. Besides gasping for breath, other clinical signs include rumen distention and rectal prolapse. Treatment for bloat involves passing a stomach tube or using a trocar to relieve gas buildup and pressure in the rumen. Once a stomach tube is in place, drenching with mineral oil or tetracycline will suppress bacterial fermentation and thereby decrease gas production. Therabloat^Ò, a concentrated form of poloxalene can also be given via stomach tube to dissipate froth in the rumen.

Bloat is best dealt with by preventing the problem, rather than treating affected animals. Poloxalene (Bloat Guard) is a feed additive that helps to control frothy bloat. If alfalfa is to be grazed, allow cattle to have access to poloxalene 2 to 5 days before grazing begins and throughout the grazing period. Producers can use rotational or strip grazing so that selective grazing is not permitted. This also keeps cattle close to the Bloat Guard source. Cattle should not be allowed to overgraze a section because they may overeat when rotated to fresh pasture. If alfalfa yield is 6 tons per acre, stocking rate should be 5-7 head of 400 lb. calves per acre. The first day cattle are turned onto legume pasture, wait until midday when forage is dry. In addition, delay grazing alfalfa in the vegetative stage (before 10% bloom), and keep cattle off of bloat-provoking pastures in wet weather. Other strategies include feeding harvested forage (hay) every morning before turning out on legume so that the cattle do not eat as much of the bloat-causing forage. Using mixed pastures (not 100% alfalfa) will also decrease risk. Monensin is beneficial in preventing legume bloat, but not as effective as poloxalene. Because lasalocid is not as anti-protozoal as monensin, it is not effective in reducing the risk of pasture bloat.

            Grain bloat is the other form of frothy bloat. Cases of grain bloat tend to last at least 14 days in comparison to the short duration of pasture bloat prior to death. As the name implies, in cases of grain bloat, grain exceeds 50% of the diet and good quality hay and additional protein increase the severity. Grain bloat is more common if rations are stepped-up rapidly, and the hay and grain are ground. Animals that eat rapidly are at higher risk, as are animals with poor rumen motility. Grain bloat is caused by the release of polysaccharide foaming agents in certain rumen microbes as they die. If large populations of these bacteria die in a short period of time (acidotic event), frothy bloat may occur. Poloxalene is not an effective preventative for grain bloat. However, both monensin and lasalocid have been demonstrated to decrease risk.

            Free gas bloat is not as common as frothy bloat and occurs when an animal cannot eructate (belch) for reasons other than froth. Blockage of the esophagus because of nerve damage, a tumor, or abscess are uncommon reasons that free gas bloat occurs. This type of bloat also occurs when rations are changed quickly from high forage to high concentrate causing rumen pH to decrease, and rumen motility to slow or stop.

Acidosis

Dietary changes in cattle are common. Changes in roughage source are usually well tolerated; the exception is frothy bloat caused by legume plants or wheat pasture. In contrast, change from a roughage diet to a concentrate diet is often accompanied by subacute or primary acidosis. Following ingestion of large quantities of feeds rich in readily fermentable carbohydrates, an aberrant cycle of fermentation occurs causing rapid production of ruminal organic acids (VFA + lactic). The rate of lactic acid production exceeds its rate of fermentation. Fiber-digesting bacteria are sensitive to lower pH in the rumen. As the pH in the rumen declines (becomes acidic), these bacteria are destroyed, releasing endotoxins into the ruminal fluid. Lactic acid-fermenting-bacteria also decline in numbers as pH decreases, the end result of which is a profound ruminal and systemic lactic acidosis and a variety of secondary disease processes, any of which may be life threatening. Increased lactic acid in the rumen causes a further pH decline, a decrease in rumen motility and an increase in the osmotic pressure across the rumen wall, leading to water being drawn out of the blood and tissues and into the rumen. Acidosis is usually accompanied by diarrhea.

            In the blood, lactate concentration increases, pH declines, and dehydration occurs due to the osmotic gradient into the digestive tract. The clinical signs that are evident as a result of acidosis can closely resemble those of respiratory disease: lack of appetite, slow movement without “purpose”, increased heart rate and respiratory rate, and elevated body temperature.

When gram-negative bacteria die in large numbers early in the course of acidosis, large amounts of endotoxin are released and absorbed directly through the rumen wall. Endotoxic animals can show signs such as laying on their side, diarrhea, shock, and white blood cell abnormalities. Bacteria are also absorbed directly into the portal circulation and may travel to other organs.

Following an acidotic event, calves may develop liver abscesses, laminitis, or polioencephalomalicia. Liver abscesses are caused when bacteria absorbed directly from the rumen are carried by the portal circulation and colonize the liver. Fusobacterium necrophorum and Corynebacterium pyogenes are the most common bacteria causing liver abscesses. These abscesses are local rather than diffuse, therefore, liver specific enzymes, heme metabolism and BSP clearance are usually normal. Cases of laminitis are associated with histamine and endotoxin release during acidosis.

Cereal grains such as corn, wheat, barley, sorghum (and to a lesser extent oats) as well as high sugar or starch content fruit or root crops (apples, potatoes, sugar beets etc.) are associated with acidosis. Green, unripe corn, corn or milo stubble fields, and byproduct feeds such as bakery waste, elevator fines, “Red Dog”, and brewer’s grains are also high in starch or simple sugars making cattle eating these feeds also at risk for acidosis. Fine grinding and rapid changes in diet composition or exhaustion of a primary feed source are often implicated in the disease.

Feeds that are not likely to induce acidosis are hay, ensiled forages and fiber-type byproduct feeds. Hay does not contribute to acidosis because the energy source is mostly cellulose rather than simple sugars and the physical properties (large particle size) resists rapid fermentation. Ensiled forages have already gone through fermentation, thereby decreasing their risk. Fiber-type byproduct feeds such as soy hulls or corn gluten feed are similar to hay in that the energy source is primarily cellulose with little starch or simple sugar present.

Acidosis is controlled by stepping up rations slowly. If cattle are going to be placed on full feed, four step-up diets are routinely used and animals are on a full feed (64 Mcal) diet by 30 days. Some producers step-up rations more quickly (i.e. 21 or even 14 days), however the incidence of acidosis will increase. Inclusion of an ionophore in the ration helps to decrease the incidence and severity of acidosis, while dietary buffers (sodium bicarb) have not been shown to be a reliable control method.

Coccidiosis

            Coccidiosis in cattle is caused by a protozoan parasite that invades the cells of the intestinal tract. The organism damages the intestinal lining, thereby reducing the animal's ability to gain weight and in some cases, can cause severe bloody scours, and dehydration. Although almost all mammals can be infected with coccidiosis, the organism does not spread from one species to another. In other words, cattle can not be infected with coccidia from pigs or any other species. Sixteen species of Eimeria are known to infect cattle. Eimeria bovis and Eimeria zuernii are highly pathogenic; E. auburnesis and E. alabamensis are moderately pathogenic and E. ellipsoidalis is less pathogenic. In outbreaks of bovine coccidiosis, the most frequently seen coccidia oocysts are E. bovis and E. zuernii followed by E. auburnesis and E. ellipsoidalis.

Coccidia organisms are very common and most farm animals are infected, but only a limited number suffer from disease; in other words, infection by no means consistently leads to disease. Cattle acquire the infection by ingesting feed or water contaminated with immature stages of the coccidia organism. Severity of coccidiosis depends on the number of the organisms in the intestinal tract. If only a few are ingested, no symptoms may occur, and repeated mild exposure may produce immunity to the organism without disease. If a moderate number are ingested, the disease may be mild and immunity may result. If however, poor sanitation, crowding, or stress, increases the number of organisms ingested or the ability of the organisms to multiply rapidly, severe disease and even death can result. Coccidiosis is most common in young animals because they have limited immunity to the organism. Adult animals that remain in the herd are usually immune to the local coccidia. However, brining in new animals can cause an outbreak of coccidiosis in the new additions, or the new animals may bring in a new species of coccidia and cause an outbreak in the original herd. Outbreaks of the disease are common in calves stressed by weaning, bad weather or malnutrition.

The signs of coccidiosis include diarrhea or soft feces containing blood, a rough hair coat, poor weight gain, rectal straining or prolapse, and occasionally in severe infections, nervous system problems such as staggering, and seizures. Although other diseases will cause a bloody diarrhea, coccidiosis is a common culprit if blood is found in the feces. Oocysts are usually demonstrable in the feces if E. bovis is involved. If E. zuernii is involved it may or may not be demonstrable in the feces. If it is causing disease while in the schizont phase of the life cycle, there may not be any oocysts. In heavy infections, microscopic examination of the feces may reveal the presence of merozoites, gametocytes, blood cells, and sloughed intestinal mucosal cells in addition to oocysts.  Occasionally, severe infections may cause so much destruction to the intestinal mucosa that no coccidian oocysts appear the feces.  In these cases, diagnosis depends on finding coccidian stages in the intestinal tract by microscopic examination.

The immunity to coccidiosis is not well understood. Immunity is species specific. For example, animals that are immune to one species of coccidal organisms are still susceptible to the fifteen other species. In addition, breakdowns in immunity associated with either extremely high exposure or stress-related immune suppression do occur. Cell-mediated immune responses appear to be more important than humoral responses, but antibodies also appear to provide a certain degree of protection against recurrence of the disease.

Good animal husbandry practices to improve sanitation and reduce stress, and the proper use of anticoccidial drugs are the only effective means of controlling the disease. Limiting exposure to the organisms is of prime importance because using anticoccidial drugs in a heavily-infected environment provides marginal control.

The immature stages of the coccidia organisms develop very fast, and survive well in moist, shaded areas. They are fairly resistant to common detergents and can survive freezing temperatures. Exposure to sunlight (at least 4 to 8 hours) and dryness (humidity less than 25%) are probably the best methods to kill the immature forms of the organism found contaminating the environment. Therefore, designing facilities that avoid moist, shaded areas combined with proper manure management greatly decreases the risk of clinical disease.

            Coccidiostats in receiving rations provide effective control of both clinical and subclinical coccidiosis. Clinical coccidiosis in newly received calves is quite common and results in noticeable losses in production as well as in higher medication costs and deaths. Treatment options include amprolium (Corid) added to the feed or water at the rate of 10 mg/kg for 5 days or sulfa products for 5 days to bring clinical cases of coccidiosis under control. There are several options to prevent coccidiosis in susceptible calves or once a clinical outbreak is under control. Decoquinate (Deccox) can be included in the feed at a rate of 22.7 mg/100lbs of body weight. It should be added to the feed for at least 28 days during coccidiosis exposure or during periods when coccidiosis is likely to be a hazard such as calves arriving in a backgrounding lot. If amprolium is used as a preventative, not a treatment, include it at the rate of 5 mg/kg in either the feed or water for 21 days. The ionophores monensin (Rumensin) and lasalosid (Bovatec) do not act to treat active cases of coccidiosis, but do kill late stages of the parasite, thereby preventing clinical cases of coccidiosis. 

            Of great importance to cattlemen are sub-clinical cases of coccidiosis. In these cases, the calves do not have bloody scours, but have reduced performance and increased incidence of other stress-related disease, including pneumonia. Improved average daily gain and feed efficiency result from the use of a coccidiostat during the receiving period. Rumensin or Bovatec can be placed in the ration after the calves have begun consuming normal quantities of feed, generally at about 3 weeks after arrival. These ionophores act to provide a continuous control of coccidia to prevent performance losses from this costly parasite.

Footrot

            One of the most common health problems that face cattle both in range situations and in drylots is infections of the soft tissues and occasionally the bones of the foot. Footrot in cattle is caused by foot injury that damages the skin between the claws or at the base of the foot that allows bacteria to enter the skin and cause infection. The bacteria that cause footrot are very common and present in all feedlots and pastures; however some pens have a higher prevalence of the disease than other pens. Exposure to manure, stalk fields, frozen rough ground or extreme drought can contribute to infection because of skin damage and increased exposure to the offending bacteria. Footrot is usually a seasonal disease occurring during periods of extreme moisture or severe drought and also when muddy yards are frozen resulting in very rough conditions.

            The first sign of footrot is lameness that may range from very mild to being serious enough that the animal is reluctant to move. Close examination of the involved hoof will indicate inflammation extending into the hock joint with fluid coming from the hairless skin at the top of the cleft between the claws, along the coronary band or the bulbs of the heels. It is important to differentiate footrot from cases where the hoof is damaged by nail penetration, injury from glass or other sharp objects, or from sole abscesses.

            Any management procedure that will eliminate hoof damage will contribute to the prevention of footrot. Thoroughly cleaning pens after cattle are removed and liberally spreading lime over the pen surface can avoid many of the problems of foot rot. Maximum drainage is an absolute essential to any feedlot arrangement and will aid in preventing the constant contact with manure-laden mud or water. Well-built and maintained mounds are good protection from footrot. The mounds should be arranged so that they receive maximum exposure to the sun, and should be spread with lime occasionally. Frozen rough ground in lots can be corrected by spreading salt or fertilizer, which softens the frozen soil and may also counteract some organisms. Covering the frozen ground with straw may also be helpful in preventing foot injury. Concrete slabs placed around water fountains and feed bunks, where animals frequently congregate are very helpful in preventing contact with extremely muddy conditions.

            The addition of Ethylene Diamine Dihydriodide (EDDI) in salt or feed is often suggested as a footrot preventative measure. Use of doses greater than the approved level may result in irritation of the respiratory tract with signs similar to IBR infection. If many animals in a herd or pen are affected, the problem may be treated with feed-grade tetracycline antibiotics if cattle consume adequate dosages. Use of lower dosages will not cure infections and leads to chronic footrot. EDDI in the feed or salt may be of some help but is usually considered a preventative at best.

“Brainers”- Central Nervous System Disease

            The case fatality rate of cattle with CNS disease is generally high, and although most causes of CNS disease cannot be passed to humans, rabies is an exception.

Rabies

            Rabies is extremely rare in stocker and feedlot cattle, but it does occur. Because of the dangers associated with the spread of rabies from animals to humans, extreme care should be taken when treating cattle with CNS disease or when removing the brain at necropsy from animals that die with signs of CNS disease. Protective clothing, gloves, and a facemask are required when dealing with potential rabies cases. Rabies cases do not respond to treatment and the disease has a 6- to 7-day course, with death occurring 48 hours after the animal becomes recumbent.

Polioenchephalomalacia (Polio or PEM)

Polioencephalomalacia is a general term used to describe a brain lesion that can be caused by a variety of neural metabolite disruptions such as sulfur toxicity, thiamine deficiency, acute lead poisoning, and sodium toxicosis/water deprivation. Polioencephalomalacia is characterized by a sudden onset of aimless wandering, blindness, head-pressing, ataxia, muscle tremors, with severe cases exhibiting opisthotonus, lateral recumbency and convulsions. Necropsy lesions include necrosis of cerebral gray matter with sparing of adjacent white matter. Histologically, the lesion is characterized by edema, neuronal necrosis, gliosis, and neuronophagia.

Sulfur-induced Polio - Young cattle (6-18 months old) are especially vulnerable. The disease is usually manifested at least one to three weeks after initial exposure to a diet high in sulfur. Even though a moderate intake of dietary sulfur may cause this disease, not all cattle subjected to naturally occurring high-sulfate diets actually develop clinical signs (10-35%). Current knowledge of all nutritional factors that interact to cause sulfur-induced polioencephalomalacia is not complete, but thiamin or cobalt deficiency, carbohydrate source, ruminal fluid pH, among others may be involved.

High-concentrate diets (high in readily fermentable carbohydrates) that are high in sulfate and low in long fiber have been shown to induce polioencephalomalacia. These diets increase rumen sulfide concentrations, but do not alter thiamine status or its mono- or diphosphate esters in whole blood, brain, cerebrospinal fluid, or liver (which would indicate thiamine deficiency). In addition, it has been shown that sulfide causes polioencephalomalacia directly, not by a rumen-derived neurotoxin as product of disturbed ruminal metabolism. Sulfide is normally produced by rumen microbes, and under conditions of high dietary sulfate intake, the capacity for microbial sulfide production increases. Hydrogen sulfide (H₂S) is highly neurotoxic and when present in rumen gas that is eructated and inhaled, may cause the lesions described. The relative concentrations of H₂S in the rumen gas cap and the hydrosulfide anion in the rumen fluid change with pH. Acidic conditions favor an increased rumen gas cap concentration of H₂S.

For diagnosis of sulfur-induced polioencephalomalacia, it is important that total sulfur (water and feed) intake be considered. The recommended level of dietary sulfur is less than .3% and the maximum tolerated total intake level of 0.4% (as dry matter intake) is known to cause polioencephalomalacia in cattle. Cattle rations often contain 0.15-0.2% sulfur as dry matter. Feeds that are high in sulfur include: water, molasses, beet pulp, gypsum (CaSO₄; used as an intake limiter in self-fed diets), ammonium sulfate (acidifies urine and is used to prevent urinary calculi), some grain-processing-by-product feeds such as corn gluten feed, and cruciferous plants (mustards), bracken fern and nardo fern. A moderate sulfur content in water of 1000 ppm as sulfate may easily contribute 0.1 to 0.2% of dietary sulfur, pushing sulfur intake to the limit of toleration. Because of the increasing recognition that moderate intake of sulfur can cause polioencephalomalacia, sulfur toxicosis should be an important differential in ruminants presenting with the clinical signs of CNS disease, and both feed and water should be tested for total sulfur content.

            Estimation of rumen gas cap H₂S concentrations has also been described as a practical method of diagnosing sulfur-induced polioencephalomalacia. Gould, et. al. sampled rumen gas by doing a surgical preparation of the left paralumbar fossa and introducing a 8.9-cm 18-gauge cerebrospinal fluid needle with stylette in place into the gas cap. The stylette was removed and the needle was connected to a plastic guard chamber with filter that was connected to calibrated H₂S detector tube. The detector tube was attached to a volumetric gas-sampling pump. Multiple 50-mL volumes of rumen gas were aspirated until a reading was evident in the detector tube. Readings were usually obtained after aspiration of 50-300 mL of gas. Steers that were experimentally fed high levels of sodium sulfate had significantly greater H₂S values (most were over 2,000 ppm) measured in steers consuming the same diet without added sulfate (under 500 ppm).

The following equations can be used to calculate total dietary sulfur level

(NRC max = 0.4%):

Feed:

sulfur (%) in ration (DM basis) ´ grams feed (DM)/day = grams S/day from feed

Water (sulfate is 1/3 sulfur by weight; ppm = mg/kg; 1 liter water = 1 kg):

(Sulfate (ppm) ¸ 3) ¸ 1000) ´ liters of daily water intake = grams S/day from water

Total:

[(grams S/day from feed) + (grams S/day from water)] ¸ total grams feed (DM) = % sulfur

Treatment and prevention of sulfur-induced PEM involves changing to a lower-sulfate water source, or removing or diluting high-sulfur feeds. In addition, because thiamine treatment has been shown to be beneficial in cases of lead encephalopathy, a nonspecific positive response may result from thiamine administration in cerebral diseases.

Rumen microbe-induced Polio - Polioencephalomalacia (Polio) can be caused when certain rumen bacteria, Bacillus sp and Clostridium sporogenes, increased in number during an acidotic even. These bacteria produce the enzyme, thiaminase, which block reactions in the brain that require thiamin. Sulfates are required for the formation of thiaminase, and excessive sulfates in the ration or water can aggravate “polio” problems. Failure of the brain to obtain energy causes signs of nervous system problems such as blindness, circling, head-pressing, and convulsions.

Lead-induced Polio – Lead poisoning in cattle is most commonly due to accidental ingestion of material containing lead such as paint or petroleum products. Cattle seem to attracted to materials containing lead such as machinery grease, chrankcase oil, lead batteries, linoleum, and roofing felt. Bone, liver or kidney lead levels are diagnostic for lead poisoning in samples taken at necropsy. In the living animal, blood levels of lead along with clinical signs are used to suggest lead toxicity, although blood levels alone can be misleading (primarily false negatives).

Nervous coccidiosis –

            One of the unsolved aspects of bovine coccidiosis is the occurrence of nervous signs in some animals during outbreaks of clinical disease caused by E. bovis and/or E. zuernii. This neurologic syndrome occurs primarily in calves and weanling cattle. The majority of cases occur between January and March (in Canada) when animals are often exposed to cold ambient temperatures and marginal nutrition. The syndrome is characterized by muscle tremors, staggering, convulsion, and occasional blindness, all of which appear to be similar to those observed in hypomagnesemic animals. The pathophysiology of this syndrome is not clear; antibody-antigen reactions, autointoxication, and loss of electrolytes have been suggested.

            The severe lesions in the lower ileum, cecum, and large intestine (all playing an important role in mineral absorption) may indeed cause lowered magnesium and calcium levels.  Timely treatment with parenteral magnesium, calcium, dextrose, electrolytes, and sulfamethazine appaers to alleviate the disease.

Thromboembolic Meningoencephalitis (TEME) –

            This disease is caused by the bacteria, Haemophilus somnus and if CNS signs are present, they follow respiratory, circulatory and/or musculoskeletal system (arthritis) infections. The disease appears to be more common during the fall and winter, with outbreaks following stress due to cold weather or weather change. Diagnosis must be made based on microscopic examination of brain tissue. Treatment of affected animals with antibiotics seldom results in a cure. Control or prevention of H. somnus with mass-medication of antibiotics, feeding antibiotics, or use of vaccines has failed to show consistent efficacy or economic benefit.

Listeriosis –

Listeria is a bacteria that is very common in soil and the intestine of cattle as well as on many types of hay, grass, and other crops. It needs a low-oxygen environment to multiply to dangerous levels. If Listeria is present in the feed, up to 100% of the animals in the herd may become infected with up to 10% showing signs of disease. Improperly fermented silage (still has oxygen present and pH >5.5) is a good environment for Listeria to grow. Listeriosis can present as circling, tremors, stumbling, ear droop or lip droop on one side. Tentative diagnosis is based on history of nervous system disease and a silage-based diet. Spinal fluid samples also help diagnose the problem. Final Diagnosis is done by identifying brain lesions at necropsy. Serology (serum antibody titers) are not helpful in making a diagnosis (many animals have a titer). Listeria can be passed to humans with serious results – it is usually passed via milk, meat, eggs.

Summary

            Although a number of other diseases affect stocker and backgrounding cattle, this summary covers the majority of problems faced by weaned calves and yearlings. Control of these diseases relies on a good purchasing procedure, minimizing stress during transport and after arrival, proper use of vaccines and other health products, and adequate nutrition at arrival and later during the backgrounding/stocker period. Problems in any of these areas will greatly increase the risk of illness and death, as well as poor performance.