My presentation is about bovine neonatal diarrhea, more commonly referred to as calf scours. As always, good management is an important factor when

Transcription

1 My presentation is about bovine neonatal diarrhea, more commonly referred to as calf scours. As always, good management is an important factor when dealing with herd health. This applies to calf rearing as well. With appropriate management, having less than 5% calf loss due to diarrhea is a realistic goal. 1

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3 There are two main mechanisms for diarrhea. They are increased secretion and malabsorption. Some bacterial organisms (including ETEC and Salmonella) secrete endotoxins that induce increased secretions of the intestinal tract. Malabsorptive processes are often caused by destruction of the intestinal epithelium Protozoa and viruses fall into this category. Secondary effects of diarrhea include bacterial overgrowth in the gut due to excessive nutrients that cannot be absorbed. The osmotic effect of these excessive nutrients draws more water into the intestine, further exacerbating the diarrhea. Inflammation of the gastrointestinal tract, especially due to salmonellosis and clostridiosis, creates an environment with increased mucosal pore size, releasing prostaglandins (which have secretory affects as well), and by destroying intestinal cells who deal with absorption. The calf becomes ill when output exceeds intake, and fluid and electrolyte losses create dehydration. Acidosis may occur as a result of loss of bicarbonate through the fecal route, and lactic acid production by poorly perfused tissues and fermenting bacteria. If the disease progresses, depression leads to loss of the suckle reflex. Recumbency and coma with death follow. Causes of death include hypokalemic heart failure (loss through GI tract and extracellular redistribution due to acidosis), hypoglycemia, and bacterial endotoxin release. 3

4 There are four main classes of causes for calf scours. 4

5 E. coli is a member of the normal gut flora. There are three strains listed that are pathogenic and can be included in the disease process. ETEC has both virulence factors and pili which increase its virulence. There is an age dependent susceptibility to ETEC, and the window in which calves are susceptible to the pili is until day 3 unless simultaneous infection with rotavirus occurs (which increases susceptibility to day 7-14). AEEC and STEC work via damage to the intestinal mucosa. The window of susceptibility is from day 2 to 4 weeks of age. With Salmonella, serogroups B, C, D, and E are involved with 95% of Salmonella associated disease. Other systemic signs are commonly concurrent with Salmonellosis, including anorexia, fever, and depression. Severe inflammation of the gastrointestinal tract can occur. The main source of infection is from contamination (colostrum, equipment, feeding buckets, human transmission). Cleaning and disinfection of feeding objects is helpful. Clostridium is not an important role player in calf scours but should in the least be mentioned. 5

6 Rotavirus: Rotavirus is the number one cause of neonatal calf diarrhea, affecting claves from 5 days to 2 weeks of age. In calves who have not received colostrum, rotavirus can invade within 24 hours. Colostral antibodies against rotavirus play a large role in protecting the calf for up to three days. Intestinal villus enterocytes are attacked by rotavirus, destroying them faster than they can be replenished. It is believed that the most common source of infection is maternal shedding of virus during pregnancy and especially parturition. Infected calves then spread the disease to other calves. It is also a hardy virus and can survive in water and soil for months if temperatures are less than 5 degrees C. Coronavirus: Coronavirus occurs in calves from 5 days of age to 1 month of age. Again, lack of colostrum can create disease within 24 hours of birth. Routes of infection include both respiratory and oral routes. Viral shedding is problematic, and can occur up to 2 weeks in nasal shedding. Older calves may also suffer from respiratory infections. Like rotavirus, infection comes from persistently infected cows, and viral shedding by the mother increases at parturition and also during winter thusly making winter infections more common. Coronavirus is more severe than rotavirus, causing mucohemorrhagic enterocolitis. Bovine Virus Diarrhea BVD : This is rare in neonatal calves and can occasionally cause diarrhea. BVD type II infections can cause neonatal outbreaks, which include intestinal ecchymotic and petechial hemorrhages. BVD can cause oral ulcerations, which can be differentiated from bovine papular stomatitis by their lack of epithelial proliferation. Most often, colostrum protects calves from BVD. Bovine Torovirus: This virus is part of the Coronaviridae family. It can cause diarrhea 6

7 (Coccidiosis) Eimeria: E. bovis and E. zuernii are the two most common pathogenic species. Transmission is fecal-oral by ingestion of oocysts that activate in the environment. Oocysts survive cold temperatures but cannot survive dry and hot conditions. Symptoms can range from patchy areas of epithelial sloughing to extensive hemmorhage and more diffuse sloughing. Often, overcrowding creates outbreaks. Subclinical infections may occur in 95% of the calves causing diminished growth rates. Cryptosporidium: Genotype 2 is the zoonotic genotype found in both cattle, goats, and sheep. Transmission is fecal-oral via direct contact, contaminated water, and even by flies and again, adult carrier cows are thought to be a main source of infection. Colostrum can decrease infectivity by multiple mechanisms. It affects mostly the distal small intestine and is capable of autoinfection, setting up relapse. Villous atrophy and fusion with epithelial inflammatory infiltrations are common. Calves become infected from day 1 to 4 weeks, and diarrhea develops within 72 to 96 hours and can go on for 8 to 23 days with oocyst shedding. Oocysts are are unfortunately resistant to chlorination of water and most disinfectants, but experimental models show them to be susceptible to drying. Giardia: Giardia is often found concurrently with other etiologic diarrheal agents. The degree that giardia plays as a primary pathogen is a source of debate. Again, colostrum provides protective antibodies. Giardia reduces the surface area of the microvilli, and chronic infections are common as calves have poor specific immune responses to giardia. 7

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10 Ultimately, it is important to diagnose ETEC and Salmonella as they can be controlled with vaccines and antibiotics. Both salmonellosis and cryptosporidiosis are important for public health. 10

11 Often, outbreaks of diarrhea are multifactorial in nature. It is therefore important to ensure that risk factors are minimized. With colostrum quality, a lower volume is desired to decrease antibody dilution. Genetics and dam nutrition also play a role. First and second parity cows have lower colostrum concentration, and climate temperature extremes lead to decreased immunoglobulin concentration as well. The ideal colostrum is low in volume, from a dam with good genetics and nutrition, in her third lactation or higher, during a season without temperature extremes. 11

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13 The most common cause of death in these calves is dehydration and acidosis. Milk withdrawal can help, as it will decrease the osmotic effect of the unabsorbed milk diminishing bacterial overgrowth and undesirable fermentation (with production of organic acids). Reintroduction can be done in small amounts after the calf has their suckling drive reinstated. Antibiotic therapy may decrease mortality and shedding, but some controversy exists over their use. Some question efficacy, and worry about developing resistance. Therapy may be directed at specific pathogens or may be used to help decrease the risk for bacteremia. Emphasis should be placed on gram organisms (ie E. coli). Susceptibility should also be determined, based on blood or tissues from bacteremic calves. Ceftiofur has an ideal spectrum of activity when given parentally (dosing 5 mg/kg for 5 days). Antiprotozoals include halofuginone (licenced in Europe for Cryptosporidium in calves), coccidiostat medicated pellets (monensis, lasalocid, amprolinum, decoquinate), and fendbendazole for Giardia. 13

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