Viral

Bovine rota virus

- Diarrhoea in calves at 1 to 2 weeks of age very short incubation period (12~24 h) and induces peracute diarrhea in affected calves.

- the calves shed a large amount of virus via feces for 5~7 days, thus contaminating the environment and allowing the virus to be transmitted to others

Bovine coronavirus

Three distinct clinical syndromes in cattle:

a) calf diarrhea in calves at 1 to 2 weeks of age;

b) winter dysentery with hemorrhagic diarrhea in adult animals; and c) respiratory diseases including bovine respiratory disease complex in both young and adult cattle

Bovine viral diarrhea

- Most infected animals develop mild clinical signs such as low-grade fever, leukopenia, anorexia, and decreased milk production

- Acute BVD infection is characterized by diarrhea, pyrexia, depression, anorexia, decreased milk production, oral ulcerations, hemorrhagic syndrome, and lymphopenia/leucopenia leading to immunosuppression

some infected cattle occasionally harbor the virus for a long time with periodical appearance of transiently detectable viremia from time to time

Bacterial

Salmonella

S. enterica serovar Typhimurium (S. typhimurium) and serovar Dublin (S. dublin) are the most common etiologic agents that cause salmonellosis in cattle

Acute diarrheal disease is most common with S. typhimurium and systemic disease is associated with S. dublin. Calves less than 3 weeks of age are commonly infected by Salmonella

watery and mucoid diarrhea with the presence of fibrin and blood

The lesions frequently observed in affected calves involve the pseudomembrane on the mucosa of the small intestine as well as enlargement of the mesenteric lymph nodes.

Calves can shed the organism for variable periods of time and intermittently depending on the degree of infection (e.g., clinical or subclinical infection).

Escherichia coli

The most common cause is ETEC stains that produce the K99 (F5) adhesion antigen (commonly referred to as E. coli K99+) and heat-stable enterotoxin

Neonatal calves are most susceptible to ETEC infection during first 4 days after birth and develop watery diarrhea

six pathogroups based on virulence scheme: enterotoxigenic E. coli (ETEC), shiga toxin-producing E. coli, enteropathogenic E. coli, enteroinvasive E. coli, enteroaggresive E. coli, and enterohaemorrhagic E. coli.

Clostridium perfringens

-  Five toxin types (A, B, C, D, and E) based on the production of four major toxins: alpha (α), beta (β), epsilon (ε), and iota (ι).

-  Enterotoxin causes diarrhea and intestinal cramping due to its effects on epithelial tight junction protein. Beta-2 toxin, which is produced by all types of C. perfringens

The affected calf is usually in good health condition

Parasitic

Coccidiosis

In cattle, oocyst counts of greater than 500 per gram of faeces in combination with typical clinical signs are highly suggestive of coccidiosis

-  diarrhoea, typically containing blood and mucus.

-  Mild cases have watery diarrhoea without blood.

- Calves may prolapse their rectum from repeatedly straining.

-  Reduced feed intake and poor growth rates.

- Typically affects group reared calves at 8-12 weeks.

- E. bovis E. zuernii

- E. auburnensis are the the most common Eimeria species encountered

Cryptosporidium parvum

-  Cattle are commonly infected by C. parvum, C. bovis, C. ryanae, and C. andersoni. C. parvum is considered to be primary cause of calf diarrhea

C. parvum is considered the primary cause of calf diarrhea and is a potential zoonotic agent

II- Non-infectious causes diarrhea

Nutritional cause of diarrhea

-  Nutritional deficiency of copper related to excess molybdenum in diet (secondary deficiency) can cause profuse diarrhea in calf called teart or peat scour.

History of feeding high concentrates

Dietetic diarrhea

·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

History of change of diet

Antibiotic related diarrhea

·oral administration of antimicrobials such as neomycin or tetracycline to young calves for 3–5 days can result in villous change with resultant malabsorption and mild diarrhea.

·Prolonged and high-dose antibiotic treatment of calves can lead to diarrhea associated with intestinal dysbiosis (destroy normal microflora)

History of treatment with antibiotics for prolonged periods