Bovine pneumonia or Bovine Respiratory Disease is a devastating condition affecting cattle of all ages. It is the most common cause of mortality in all ages of cattle except young calves. It is most often associated with the assembly of large groups of cattle from diverse origins. The disease is of considerable economic significance in feedlots, it is responsible for a high mortality rate and the condemnation of infected carcasses at slaughter.

The most important infectious agents involved are viruses and bacteria. They are as listed: Infectious bovine rhinotracheitis virus (IBR) Mannheimia haemolytica Bovine respiratory syncitial virus (BRSV) Pasteurella multocida Bovine parainfluenza 3 virus (PI3) Haemophilus somnus Bovine viral diarrhoea virus (BVD) Mycoplasma spp Chlamydia spp. Salmonella spp. Parasites occasionally contribute to clinical disease.

Antibiotics can be used to combat bacteria but are ineffective at fighting viruses.

Proper animal management helps to make outbreaks of respiratory disease self-limiting and even clinically unapparent. Stress, poor nutrition, and high worm burdens render animals more susceptible to outbreaks of respiratory disease, by their negative impact on host immune status. The bacteria Mycoplasma spp. and Chlamydia spp. are considered significant predominantly in younger stock.

Respiratory disease in cattle is rarely caused by a single agent – it becomes a more complicated problem to solve when you are dealing with two, three or more agents. Knowing the problem allows you to solve it.

Signs relating to Respiratory Disease

• Fever (as high as 42 C)
• Depression, laboured breathing and increased respiratory rate
• Loss of appetite and cough
• Reddening of the mucous membranes
• Nasal discharge – Initially watery and later may become purulent
• Conjunctivitis – runny eyes
• Drop in milk production

CONTROL

Control of Bovine Respiratory Disease is based on four equally important aspects:

Vaccination – The use of vaccines confers clinical protection and more importantly reduction of the pathogen circulation. Due to the complex cause of the disease, multivalent vaccines are preferred.

Management – Reduction of circulating viruses and bacterial shedding can be achieved with careful attention to detail. Significant issues in need of address include ventilation in housing, drainage, mixing of age groups, overcrowding and parasite control. Isolation of clinically affected cases and treating with an appropriate antibiotic can also limit losses.

Biosecurity – Maintaining biosecurity involves avoiding introduction of infected animals into the herd and/or implementing stict isolation / quarantine of introductions until proven negative, and restricting access of livestock to external sources of infection e.g. double fencing is in place at all perimeters, considering carefully sources of biological materials such as embryos, semen etc.

Treatment – Therapy is limited to the use of antimicrobials and anti-inflammatory drugs. Antibiotics are only effective against bacterial infections.

Bovine viral diarrhea (BVD) is most common in young cattle (6–24 mo old). The clinical presentation can range from inapparent or subclinical infection to acute and severe enteric disease to the highly fatal mucosal disease complex characterized by profuse enteritis in association with typical mucosal lesions. BVD must be distinguished from other viral diseases that produce diarrhea and mucosal lesions.

Treatment of BVD remains limited primarily to supportive therapy. Control is based on sound management practices that include use of biosecurity measures, elimination of persistently infected cattle, and vaccination.

BVD – like any viral disease – is not treatable. Affected animals suffer severely from the infection. The disease can cause a variety of clinical symptoms, including immunosuppression (i.e. the reduced activity of the immune system to fight back other pathogens), infertility, abortions and congenital defects in calves. Some animals may develop a more severe condition known as mucosal disease, the result of which is a high mortality rate in affected animals.

BVD also has a heavy economic impact on cattle farmers due to decreased weight gain, decreased milk production, reproductive losses, or even the death of the infected animals. Most of the animals show symptoms that can be confused with other diseases; this makes the detection and control of this concealed disease even more complicated.

Clostridia are the oldest known disease causing agent (pathogen) affecting livestock and other species. They are not contagious but are highly infectious and are ubiquitous worldwide.

Blackleg

Bacterial spores are found in soil and enter the animal via the oral route. They lodge in the spleen, liver and intestine of normal animals. Subsequently they proliferate under some unknown stimulus and cause disease. Animals at risk are mainly cattle between 6 months and 2 years that are rapidly growing on a high nutrition plane. Disease can sometimes occur in sheep. It is a gangrenous disease of muscle and can be caused by a variety of clostridia as follows:

• “True” blackleg = Cl. chauvoei
• “False” blackleg = Cl. septicum and Cl. novyi
• Often see the three clostridia in combination

Tetanus

This organism, C. tetani is found in soil and manure. When it is taken in by infecting a deep wound or (rarely) orally, it can proliferate and produces a potent toxin affecting the nervous system. Variable species sensitivity exists with horses the most sensitive and cattle the least. Examples of common entry points include via deep puncture wounds, sole punctures, parturition tears, post castration and docking and after the use of elastrators. Disease is usually sporadic and outbreaks are rare.

Clinically tetanus is characterized by hyperaesthesia (they over-react to touch), prolapsed 3rd eyelid, restricted jaw movement, tetany (muscle rigidity) and ultimately convulsions. Clinical signs of tetanus may not appear for days or weeks following tissue inoculation. Affected animals will demonstrate muscle stiffness that progress to tremors and a stiff gait. A saw horse stance may develop and animals may fall and be unable to rise. Cattle will typically develop bloat and can die in five to ten days if left untreated. Animals often die due to asphyxia. Clinical pathology testing and necropsy will seldom yield a definitive diagnosis. The incubation time can be days to weeks.

Malignant Oedema

Caused by C. septicum (or occasionally C. chauvoei) which is found in gut and soil, this disease results from contamination of tissues due to deep penetrating wounds becoming infected with this bacterium. The organism proliferates in poorly perfused damaged tissue and elicits toxins which cause mortality – the animal is often just found dead. On post mortem examination tissues may be oedematous, with emphysema, malodour and swelling obvious.

Black Disease

This disease affects young adult sheep or occasionally cattle usually aged 1 to 4 years. Once taken in orally the organism lodges and waits in liver. Liver damage, caused by immature fluke tracking through, initiate disease.
Clinical Signs include stiffness, severe depression and sudden death. It most often occurs in acute fluke season though can occur sporadically at other times, especially in cattle. Clinical disease lasts 1 or 2 days and findings on post mortem examination include rapid putrefaction of carcass with black discoloration under the skin.

Clostridium perfringens infections

Infections with C. perfringens Types A, B, C or D can lead to enteric effects in animals. The organisms are usually found in the soil and intestinal tract and can proliferate in times of sudden dietary change. Clinical signs are most commonly of sudden death, though affected animals may show severe diarrhoea or gas gangrene of tissues prior to death. Outbreaks can occur. Characteristic pathology on post mortem examination include haemorrhagic enteritis, intestinal mucosal ulceration, diarrhoea contents in the intestines and evidence of dysentery. Affected animals are usually young.

Coccidiosis is usually an acute invasion and destruction of intestinal mucosa by protozoa of the genera Eimeria or Isospora. Clinical signs include diarrhea, fever, inappetence, weight loss, emaciation, and in extreme cases, death. However, many infections are subclinical. Coccidiosis is an economically important disease of cattle, sheep, goats, pigs, poultry, and also rabbits, in which the liver as well as the intestine can be affected.

Coccidiosis is seen universally, most commonly in young animals housed or confined in small areas contaminated with oocysts. Coccidia are opportunistic pathogens; if pathogenic, their virulence may be influenced by various stressors. Therefore, clinical coccidiosis is most prevalent under conditions of poor nutrition, poor sanitation, or overcrowding, or after the stresses of weaning, shipping, sudden changes of feed, or severe weather. In general, for most species of farm animals, the infection rate is high and rate of clinical disease is low (5%–10%), although up to 80% of animals in a high-risk group may show clinical signs.

Clinically healthy, mature animals can be sources of infection to young, susceptible animals.

 Signs of coccidiosis are due to destruction of the intestinal epithelium and, frequently, the underlying connective tissue of the mucosa. This may be accompanied by hemorrhage into the lumen of the intestine, catarrhal inflammation, and diarrhea. Signs may include discharge of blood or tissue, tenesmus, and dehydration.

Prevention is based on limiting the intake of sporulated oocysts by young animals so that an infection is established to induce immunity but not clinical signs. Good feeding practices and good management, including sanitation, contribute to this goal. Neonates should receive colostrum. Young, susceptible animals should be kept in clean, dry quarters. Feeding and watering devices should be clean and must be protected from fecal contamination; this usually means feed is placed in troughs above the ground and positioned so that it is difficult for fecal contamination of feed to occur. Stresses (eg, weaning, sudden changes in feed, and shipping) should be minimized.

Preventive administration of coccidiostats is recommended when animals under various management regimens can be predictably expected to develop coccidiosis.

Continuous low-level feeding of decoquinate, lasalocid, monensin, or amprolium during the first month of feedlot confinement has been reported to have preventive value.

Diarrhea is common in newborn calves, lambs, and kids. The clinical presentation can range from mild diarrhea without systemic disease to profuse, acute diarrhea associated with rapid dehydration, severe disturbance of acid-base and electrolyte balance, and death, sometimes in as few as 12 hr.

Several enteropathogens are associated with diarrhea in neonates. The most prevalent infections in most areas are Escherichia coli, rotavirus, coronavirus, and Cryptosporidium parvum. Cases of neonatal diarrhea are commonly associated with more than one of these agents, and the cause of most outbreaks is multifactorial. Determining the particular agents associated with an outbreak of diarrhea can be important, because specific therapy and prophylaxis are available for some. Also, some agents have zoonotic risk. Diarrhea is also present in septicemic colibacillosis.

E coli is the most important bacterial cause of diarrhea in calves during the first week of life. Strains in calves most commonly possess K99 (F5) or F41 fimbrial antigens, or both.

Salmonella spp, especially S Typhimurium and S Dublin, but occasionally other serovars, cause diarrhea in calves 2–12 wk old. Salmonellae produce enterotoxins but are also invasive and produce inflammatory change within the intestine. In calves, infection commonly progresses to a bacteremia.

Viruses

Rotavirus is the most common viral cause of diarrhea in calves and lambs. Groups A and B rotavirus are involved, but group A is most prevalent and clinically important. With virulent strains of rotavirus, the loss of enterocytes exceeds the ability of the intestinal crypts to replace them; hence, villous height is reduced, with a consequent decrease in intestinal absorptive surface area and intestinal digestive enzyme activity.
Coronavirus is also commonly associated with diarrhea in calves. It replicates in the epithelium of the upper respiratory tract and in the enterocytes of the intestine, where it produces similar lesions to rotavirus but also infects the epithelial cells of the large intestine to produce atrophy of the colonic ridges.

Protozoa

Cryptosporidium parvum (Cryptosporidiosis) is a common cause of diarrhea in calves and lambs. The parasite does not invade but adheres to the apical surface of enterocytes in the distal small intestine and the colon. This results in loss of microvilli, decreased mucosal enzyme activity with villous blunting and fusion (leading to a reduced villous surface absorptive area), and inflammatory changes in the submucosa. Mammalian cryptosporidia lack host specificity.

Cryptosporidiosis in Neonatal Calves Leaflet

Giardia duodenalis is a common asymptomatic infection in the intestine of young calves and lambs. It has been found in the feces of poorly growing calves that have a chronic mucoid diarrhea, but there is little evidence for a causative association of this organism with diarrhea in calves or lambs.

Other Causes
Calves fed large amounts of milk or inappropriately formulated milk replacers produce a large volume of feces with a greater than normal fluid content but do not have a fluid diarrhea with weight loss. Similarly, calves sucking high-producing beef cows grazing lush pasture may have loose feces. Milk replacers with poor quality, heat-denatured proteins or with excessive amounts of soybean or fish protein or carbohydrates of nonmilk origin have a higher risk of producing diarrhea.

Zoonotic Risk
Several of the agents that produce diarrhea in calves can also produce diarrheal disease in people. Cryptosporidium parvum and S Typhimurium can produce serious disease, particularly in immunocompromised individuals.

Leptospirosis is a bacterial disease resulting in abortion, decreased fertility and milk drop in cattle.

Leptospirosis is a zoonosis – it can cause disease in humans. Farmers / farm-workers, abattoir workers and vets are the main risk groups. The disease in man is usually acquired from contact with the urine, placental material or aborted foetus of an infected animal or with contaminated water. Clinical signs of the disease are flu-like, with headaches and fever, occasionally progressing to meningitis.

CLINICAL SIGNS

After the first phase of Leptospira infection in cattle, the bacteria localise in the urogenital tract. Early symptoms are usually mild and transient and are often not noticed.

Milk Drop

In cows, the first symptom is often a sudden decrease in milk yield.

Abortion

Abortions usually occur 6-12 weeks after the initial infection. If the infection occurs in the late gestation, an infected calf may be born. Diagnosis of leptospiral abortion is difficult and based on maternal and foetal serology, as no obvious lesions are associated with the infection.

Abortion rates range from up to 30% in herds not previously infected to 5% in herds where Leptospirosis is endemic.

Infertility

The greatest effects of infection on fertility are low pregnancy rates and increased culling due to low fertility.

Fasciola hepatica, the most important trematode of domestic ruminants, is the most common cause of liver fluke disease in temperate areas of the world.

Economically important infections are seen in cattle, sheep, in three forms: chronic, which is rarely fatal in cattle but often fatal in sheep; subacute or acute, which is primarily in sheep and often fatal; and in conjunction with “black disease”, which is most common in sheep and usually fatal. The prepatent period is usually 2–3 mo, depending on the fluke burden. The minimal period for the completion of one entire life cycle is ~17 wk. Adult flukes may live in the bile ducts of sheep for years; most are shed from cattle within 5–6 mo. Chronic fasciolosis can be seen in all seasons but manifests primarily in late fall and winter. It occurs as a result of ingesting moderate numbers of metacercariae over longer periods of time; signs include anemia, unthriftiness, submandibular edema, and reduced milk production, but even heavily infected cattle may show no clinical signs although their immunity to other pathogens (eg, Salmonella spp) may be reduced and reactions to the single intradermal test for tuberculosis modified.

Liver Fluke Leaflet

There are numerous species of paramphistomes (Paramphistomum, Calicophoron, Cotylophoron) in ruminants worldwide. The adult parasites are pear-shaped, pink or red, up to 15 mm long, and attach to the lining of the rumen.

Eggs are passed in the feces, and miracidiae hatch in the water and infect planorbid or bulinid snails. Development in the snail is similar to that in the life cycle of Fasciola hepatica, with the snail shedding cercariae that encyst on the herbage. In the ruminant host, the young flukes exist and remain in the small intestine for 3–6 wk before migrating forward through the reticulum to the rumen. Eggs are produced 7–14 wk after infection. Adult flukes do not cause overt disease, and large numbers may be encountered. The immature flukes attach to the duodenal and, at times, the ileal mucosa by means of a large posterior sucker and cause severe enteritis, possibly necrosis, and hemorrhage. Affected animals exhibit anorexia, polydipsia, unthriftiness, and severe diarrhea. Extensive mortality may occur, especially in young cattle and sheep. Older animals can develop resistance to reinfection but may continue to harbor numerous adult. In acute paramphistomosis there may be no eggs in the feces.

Rumen Fluke Leaflet

Salmonella, a rod-shaped gram-negative bacterium belonging to the family Enterobacteriaceae, is the causative agent of salmonellosis. Clinical disease is characterized by two major syndromes: a systemic septicemia (also termed as typhoid) and an enteritis. Other less common clinical presentations include abortion, arthritis, respiratory disease, necrosis of extremities, and meningitis.

In cattle, S Typhimurium is commonly associated with outbreaks of enteritis in calves <2 mo old, whereas S Dublin has been associated with the same condition in older calves and adult cattle.