Illini DairyNet Papers
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- The majority of death losses from calf-hood diseases are caused by diarrheal and respiratory pathogens.
- While vaccination targets protection against specific pathogens, adequate consumption of high quality colostrum will provide broad-spectrum protection against most diseases prevalent on a dairy farm.
Raising calves for herd replacements has become an economic issue on contemporary dairy farms. Some producers are choosing to send their calves off to heifer ranches. These producers have chosen to focus on the lactating herd and leave the specifics of replacement rearing in the hands of contract growers. The National Animal Health Monitoring Survey (NAHMS) Dairy 96 showed that only 4 percent of dairy producers are contracting their replacement programs (18% of herds with greater than 200 cows contract raise their heifers). The largest majority of dairy operations choose to raise their own replacements. This option offers the opportunity to maintain greater control of the heifer program. Each dairy farm has their own objectives, management styles, and facility constraints. Replacement programs need to be tailored to fit each farm's long and short term goals.
Controlling disease during the growing period is essential for an economically sound replacement program. A recent study published in the Journal of Dairy Science demonstrated that heifers affected by calf-hood diseases had higher mortality rates before first calving and were less likely to enter the milking herd. Data summarized from the NAHMS Dairy 96 shows that unweaned heifer calf mortality for all operations was 10.8 percent. The largest proportion of the loss (61%) was due to scours, diarrhea, or other digestive disorders. Respiratory problems accounted for 25 percent of the deaths while other causes accounted for 14 percent. Death loss for weaned heifers (weaning to first calving) was 2.4 percent. Again, the greatest losses were attributed to diarrheal (14%) and respiratory (45%) disorders.
Dairy producers need to focus on controlling these two disease categories in order to reduce calf-hood deaths and associated financial loss. A discussion of the common diarrheal and respiratory diseases follows. Comments concerning colostrum management and other preventive measures are included.
COMMON DIARRHEAL DISEASES
Colibacillosis - E. coli - Colibacillosis usually occurs in calves 1-10 days old. Typically, calves out of first calf heifers are more susceptible. Other associated factors include seasonal variation, overcrowding and poor sanitation which allow build up of organisms in calving pens. Milk pails and feeding equipment can become contaminated. Signs include frequent and effortless diarrhea, pasted rear quarters, fluid or semisolid malodorous feces with chunks of partially digested milk, rapid dehydration and weight loss, depression, anorexia, weakness, and death. Body temperature is normal at first but subnormal as the disease worsens. Death can occur in 3-5 days. Mixed infections can occur along with rota/corona virus and/or cryptosporidiosis. Illness can occur in up to 75 percent of calves on a farm, while death losses can range from 10 to 50 percent in unvaccinated herds.
Disease prevention is primarily achieved by early, rapid ingestion of colostral antibodies. Hours matter. A recent study showed that if colostrum was given 3 hours after infection with E. coli, the calves were protected against disease. If colostrum consumption was delayed until 4 hours after infection up to 40 percent of the calves died. All calves became ill if colostrum was given 5 hours after infection. E. coli bacterins used to prevent calf diarrhea are different from E. coli mastitis bacterins. Monoclonal antibodies work if given early (immediately after birth). Antibodies against E. coli antigens have little effect once the diarrhea has commenced, they are principally prophylactic.
Rota virus - Rota virus infections affects calves between 1 and 21 days old. The disease is characterized by sudden onset and rapid spread. Calves become reluctant to stand and nurse, mildly depressed, salivate, and have watery, yellow diarrhea. The diarrhea lasts 1-2 days and maybe longer with secondary infection (3-5 days). Under germ-free conditions rota virus infections are self-limiting and of short duration 6-10 hours (like the 24 hour flu). Serum antibodies do not protect calves from infection. As the level of colostral antibodies present in the intestines decline, calves become more susceptible.
Corona virus - Corona virus infections are similar to rota viral infections except, usually the clinical signs are more severe. Calves up to 3 weeks old can be affected. Clinical signs include sudden onset of diarrhea, moderate depression, reluctance to nurse, passage of feces containing mucus and milk curds. After 2-4 days of diarrhea, calves become severely depressed, weak, gaunt, and eventually die. Under germ-free conditions corona virus is more severe and can lead to death. Typically, corona virus is found along with other diarrheal disease agents.
Clostridium perfringens - Clostridial infections are manifested by acute deaths or severe diarrhea with abdominal pain. Calves may be bloated causing them to bellow and kick at their abdomen. Sudden death of vigorous fast-growing calves is typical. Calves surviving 4-5 hours after onset of colic may develop bloody stool. Under conditions where rich protein and carbohydrate substrate are fed (such as abrupt changes in diet), Clostridium can proliferate and produce toxins. Rapid feed changes disturbs the normal adaptive pattern of intestinal microbes. Overeating can lead to gut stasis, preventing the normal flushing of toxins. Viral infections may predispose calves to clostridial diarrhea due to altered intestinal flora and overgrowth of the organism. Clostridium perfringens Type A has been associated with abomasal ulcers in calves.
Cryptosporidiosis - Transmission of cryptosporidia is by fecal-oral route. Within the intestines auto-infection can occur in immuno-suppressed calves. The entire developmental cycle can occur within 72 hours. Natural infection occurs in calves 1-3 weeks of age. Clinical signs include increased frequency of defecation, straining, anorexia, weight loss, depression, and dehydration. Diarrhea is profuse, watery, and has a yellow color. Usually many calves are affected but few die as a direct consequence of cryptosporidiosis. There appears to be a seasonal effect with more disease occurring during fall/winter or stressful periods. Affected calves need supportive care since the disease is self-limiting and the intestinal repair can be prolonged. Cryptosporidia oocysts are difficult to detect. Routine fecal tests will not find the organism. A special acid-fast stain is required to diagnose cryptosporidiosis. Oocysts do not survive freezing or temperatures above 150o F for 30 minutes, but will survive at 40o F in liquid slurries. Bleach nor alcohol are effective at killing the oocysts. Strong Lysol (5% solution available from hardware stores) can be used to disinfect contaminated surfaces. Cryptosporidiosis is a public health hazard! In humans, clinical signs include abdominal cramps, vomiting, diarrhea, and fever (flu-like symptoms).
Coccidiosis - Like most other diarrheal diseases, coccidiosis is spread by a fecal-oral route. Coccidia oocysts must sporulate (hatch) before they become infective, so auto-infection is not possible. The incubation period is typically 17-21 days. In mild cases, calves will have diarrhea with little or no blood, anorexia and be listless for several days. In more severe cases, the feces becomes liquid with blood, mucus and strands of intestinal mucosa. These calves become emaciated, dehydrated, weak, and listless. Occasionally, fly strike occurs in warmer months. Calves that develop nervous coccidiosis will have acute diarrhea, tremors, convulsions, blindness, and death. In chronic cases, calves will have rough hair coats, drooping ears, and sunken eyes. Recovery is slow and some calves= growth will be stunted. Disease severity is determined by the number of sporulated (hatched) oocysts ingested. To control coccidiosis avoid overcrowding which leads to stress and increased exposure. Many producers are using milk replacers and calf starters medicated with decoquinate. In order to prevent coccidia infections, replacement heifer feed should contain one of the ionophores (lasalocid or monensin). Amprolium can be used for treatment or control in all ages.
Salmonellosis - Salmonellosis usually affects calves between 10 days and 3 months of age. The most common sero-types are Salmonella typhimurium and S. dublin. Disease severity will be determined by the virulence of the sero-type(s) involved, the concentration of Salmonella in environment and the immune status of the calves. Salmonella can be transmitted by fecal-oral contamination or aerosolized.
Three disease conditions occur; septicemic, enteric, and/or carrier. Calves with the septicemic form can die with no clinical signs (slight depression and in appetence) or diarrhea and colic with convulsions. The course of disease is a few hours, but rarely more than 1-2 days. The enteric form is most common. Calves will have slightly watery diarrhea, changing to voluminous feces with mucosal shreds, casts and/or blood. Initially, calves will have a fever but their temperature falls rapidly as dehydration progresses. Chronic salmonellosis is responsible for the carrier state. Carrier calves are typically 6-8 weeks old. They will have loose stool but not diarrhea. Body temperature will be normal to slightly elevated. These calves fail to thrive as evidenced by a rough hair coat and undersized body. Salmonella control is best achieved by good management practices including individual calf hutches with adequate spacing. Vaccinations have minimal effect.
COMMON RESPIRATORY DISEASES
Viral Respiratory Pathogens - Many different viruses have been found to be associated with pneumonia in dairy calves. Frequently, more than one virus is present during an outbreak of respiratory disease. In most cases, viral infections initiate the disease and secondarily, bacterial pathogens invade the damaged lung tissue. The viruses most frequently isolated from cases of calf pneumonia are Parainfluenza 3 (PI3) and Bovine Respiratory Syncitial Virus (BRSV) and Bovine Virus Diarrhea Virus (BVDV). BVDV infections in dairy calves begin as respiratory problems. Infectious Bovine Rhinotracheitis (IBR) has been associated more often with feedlot pneumonia.
Severe pneumonia outbreaks in Illinois have occurred due to BRSV. As with most respiratory diseases, BRSV infections tend to break most commonly in fall and winter months. Clinical signs include decreased feed consumption, mild depression, clear nasal discharge, salivation, tearing, rapid breathing and elevated body temperature (104-108o F). The virus progresses rapidly and occasionally the death occurs before any clinical signs are observed. In later stages of the disease, calves will begin open-mouthed breathing, frothing of saliva, and develop bottle jaw. Some calves may be seen standing over water tanks apparently unable to drink. Nearly all calves will be affected and up to 20 percent may die.
Bacterial and Mycoplasmal Respiratory Pathogens - Pasteurella sp. and Haemophilus somnus are the most common bacterial agents found in outbreaks of calf pneumonia. These organisms may be present in the nasal passages of normal, healthy calves. These bacteria invade the lung tissue damaged by toxic and/or viral agents. Typically, they exacerbate initial clinical signs and may be responsible for the most fatalities associated with respiratory disease. Salmonella sp. may also contribute to pneumonia in dairy calves.
Mycoplasmas are frequently recovered from the respiratory tract of dairy calves. Mycoplasma can complicate primary viral pneumonia or initiate lesions which lead to secondary bacterial infection. Antibiotics used to treat bacterial infections are ineffective at treating mycoplasma. Flare-ups of mycoplasma mastitis are not uncommon following outbreaks of mycoplasma pneumonia in dairy calves.
Calf-hood management practices summarized in the NAHMS Dairy 96 study shows many US dairy calves are challenged early in life. Less than 40 percent of small herds (<100 cows), separated maternity pens from lactating cows. In larger operations (> 200 cows), 87 percent had separate facilities for calving. Over half (55%) of operations used the same calving barn for a sick cow area. One third of herds (32%) did not wash teats and udders before collecting colostrum or allowing calves to nurse. Only 38 percent of farms used calf hutches. Pre-weaned heifers had physical contact with older animals in 63 percent of herds. These figures demonstrate that dairy calves may be exposed to multiple pathogens from the time they are born through weaning.
While vaccination targets protection against specific pathogens, adequate consumption of high quality colostrum will provide broad-spectrum protection against most diseases prevalent on a dairy farm. Calves are born with little or no immunity or resistance to disease and infections. The immunity that newborn calves acquire by absorbing immunoglobulins from colostrum is crucial for their survival. The quality of immunoglobulins present in colostrum is determined by the disease organisms and vaccinations to which dams have been exposed. The more diseases cows have had or been exposed to, the more varied the antibodies in their colostrum. For this reason, newborn calves raised on the same farm as their dams usually have good protection against diseases on that farm. Purchased calves and calves that are born of recently purchased cows or heifers will be deficient.
Resistance to disease in newborn calves is greatly affected by the timing of the colostrum intake and the quality of the colostrum. Calves can absorb whole antibodies through their gut wall during the first twenty-four hours of life. These antibodies then circulate in the calf's bloodstream to help fight off infections. The number of antibodies that can be absorbed is directly proportional to the timing of colostrum feeding after birth. By six hours, the ability of the gut walls to absorb immunoglobulins decreases by one third. By twenty-four hours, the gut walls can absorb only 11 percent of what could originally be absorbed. The intestinal walls eventually turn off the absorption mechanism. At this point, enzymes break down and digest all the antibodies, thus reducing their disease-fighting capabilities. Only one quarter of the antibodies calves consume reaches the bloodstream. Unfortunately, the digestive tract of the calf can absorb infectious organisms as well as antibodies. This explains why the colostrum and calves should be kept free from bacteria. The percentage of antibodies in colostrum decreases rapidly with each milking. Usually, the second milking contains 60 to 70 percent as many immunoglobulins as the first milking. The NAHMS Dairy 96 study showed that over half (52%) of operations allowed calves to nurse from their dams, while one third (38%) allowed nursing but removed calves within 24 hours. One third (33%) of producers used the first nursing to deliver colostrum, 63 percent hand fed colostrum in a bucket or bottle, and only 4 percent tube fed colostrum. Of herds that hand fed colostrum within 24 hours, only 32 percent fed four or more quarts.