The health and management of replacement animals are important components of total herd profitability. The productivity of the herd can be negatively affected by impaired growth of calves, decreased milk production of animals that experienced chronic illness as baby calves, spread of infectious diseases from calves to adult cows, increased veterinary costs, and the limited opportunity for genetic selection due to high mortality of replacement animals. Among all animals present on a dairy farm, the highest morbidity and mortality rates generally occur in baby calves prior to weaning. The National Animal Health Monitoring System (NAHMS) estimated preweaning mortality of U.S. dairy calves to be 10.8%, and the average age at first calving was reported to be 25.8 months (anonymous, 1996). The National Dairy Heifer Evaluation Project, sponsored by NAHMS, reported retrospective data on 1,811 dairy farms and prospective surveillance data on 921 U.S. dairy farms (anonymous, 1994). Preweaning calf mortality was 8.4% and 6.8% for the prospective and retrospective data, respectively. Diarrhea accounted for 52.2% of mortality, followed by respiratory problems (21.3%), trauma (2.4%), joint and navel problems (2.2%), and other or unknown causes (21.9%). Morbidity during the first 3 weeks of life was attributed to pneumonia (25%), diarrhea (29%), and umbilical disease (29%) in data obtained from 410 dairy calves born in 1990 on 18 commercial dairy herds located in New York (Virtala et al., 1996). Many diseases of newborn calves can be controlled by well-designed health management programs that define the care and housing of the dam during the periparturient period, standard operating procedures for the calving process, and the application of proper preventive measures (including sound nutritional programs) for the newborn calf. Efficient replacement programs endeavor to calve Holstein heifers that weigh 550 kg at 22.5 to 25 months of age. Healthy calves can achieve growth rates that allow them to be bred at 13 to 15 months of age and maximize the potential productivity of the overall dairy herd.
Simple exposure to infectious agents is not sufficient cause for the development of diseases in calves. In calf rearing, the difference between health and disease is very often just a slight tip of a delicate balance that weighs calf and environmental factors with the bacterial, viral, or parasitic agents to which the calf will be exposed. The infectious agents that are capable of causing scours, pneumonia, or septicemia in young calves are ubiquitous. Calves will inevitably be exposed, and several may become infected, but only a few should get a disease if the relevant risk factors are minimized and the sources of infection are diluted or bypassed.
The three most important disease problems in the young calf are septicemia, diarrhea, and pneumonia. These disease problems will be discussed, but the focus will be on recognizing the factors that put young dairy calves at risk of developing disease and the locations on the dairy that are most apt to act as the source of infection. Finally, early identification and treatment of sick calves will be discussed.
When a calf has septicemia, it has disease-producing organisms or their toxins in its blood. Septicemia in calves is usually the result of a bacterial infection that occurs while the calf is in the uterus or during, at, or immediately after birth. The route of infection can be the blood of a sick dam, an infected placenta, the calf’s umbilical stump, mouth, nose (inhalation), or wound. Septicemia is the most severe medical problem that a calf can develop because the blood-borne infection disseminates and damages many different organs. The bacteria that cause septicemia in calves, many of which are characterized as gram-negative bacteria like E. coli and Salmonella, are difficult and expensive to treat, and survival rate is low. Early signs of septicemia may be subtle but affected calves are usually depressed, weak, reluctant to stand, and suckle poorly within 5 days of birth. Swollen joints, diarrhea, pneumonia, meningitis, cloudy eyes, and/or a large, tender navel may develop. Fever is not a consistent finding in septicemic calves; many have normal or subnormal temperatures. Most septicemic calves have a history of inadequate colostrum intake.
Diarrhea is the most common cause of death in young calves and is almost entirely avoidable by good management. The highest risk period for diarrhea is from birth until about 1 month of age. Clinical signs of diarrhea begin with loose feces and can progress to a semi-comatose state (Figure 1).
Bacteria, viruses, and/or parasites cause diarrhea in calves. Usually, the calf is infected with more than one agent. Typically, the virus, bacteria, or parasite is identified from a fecal sample or from the intestines of a dead calf. The agents can be isolated from healthy calves and adult cows as well as calves with diarrhea. Some fecal bacterial isolates, E. coli, Clostridium perfringens, and Campylobacter, are normal intestinal flora. The veterinarian uses the findings from fecal or intestinal exams to determine the most likely cause of the diarrhea problem and to revise vaccination, treatment, and disinfection protocols. Knowing the potential pathogen provides insight into the infection source as well as the relevant factors that may have triggered the outbreak. When Salmonella is isolated, antibiotic sensitivity patterns guide the treatment protocols. When viruses and parasites are isolated, use of antibiotics is not indicated.
The agents commonly incriminated in calf diarrhea outbreaks are listed below. The age of onset of diarrhea can be used as a guide to the agents most likely to be involved. Unfortunately, the color and consistency of the feces are not reliable indicators of the cause of diarrhea.
Despite the fact that the agents differ, the resulting enteritis is remarkably consistent in terms of the presenting clinical picture. Calves with diarrhea consistently have some degree of dehydration. Dehydration may be life threatening and can be assessed by observation of typical clinical signs (Table 1).
Table 1. Assessing Dehydration
|Clinical Sign||Percent Dehydrated|
|Few clinical signs||<5%|
|Sunken eyes, skin tenting for 3-5 seconds||6-7%|
|Depression, skin tenting for 8-10 seconds, dry mucous membranes||8-10%|
|Recumbent, cool extremities, poor pulse||11-12%|
In most cases of fatal diarrhea, the calf dies of dehydration and loss of electrolytes, not from the infectious agents that triggered the diarrhea. Blood glucose levels are low, and hypoglycemic coma can develop in calves that are in cold housing and have milk or milk replacer withheld for more than one feeding. Electrolyte abnormalities involving potassium, bicarbonate, and sodium are frequently found, but these resolve rapidly when fluids are given to correct the dehydration and calves have access to water. For this reason, treatment of calves with diarrhea is primarily supportive. The most important aspects are early recognition and aggressive fluid therapy. Prompt treatment with oral fluids and electrolytes is necessary for successful treatment of diarrhea (Table 2).
Table 2. Fluid Requirements for Treatment of Diarrheaa
|Calf Health||% Dehydrated||Daily Milk||Oral Fluids|
|Healthy calf||0%||4.4 kg||0 kg per day|
|Mild diarrhea||2%||4.4||1.1 kg per day|
|Mild diarrhea||4%||4.4||2.2 kg per day|
|Depressed||6%||4.4||3.3 kg per day|
|Very ill||8%||4.4||4.4 kg per day|
|Recumbent||>10%||4.4||Need intravenous fluids|
|ashould be fed separately from electrolytes.|
Pneumonia is an inflammation of the lungs. Clinical signs of pneumonia include nasal discharge, dry cough, body temperature of >41°C, respiratory distress, and decreased appetite. Calves that develop pneumonia prior to weaning frequently share the same risk factors as those that develop diarrhea: failure or incomplete transfer of immunity from colostrum, prolonged exposure to adult cattle, and/or the ventilation limitations of warm housing. Large diurnal temperature variations and transportation or grouping stress can contribute to the development of pneumonia. As with diarrhea, frequently more than one agent is identified in an outbreak. Herds often experience outbreaks of pneumonia occurring in a number of calves at the same time. Antibiotic therapy is necessary but frequently yields disappointing results. Because of the significant impact that pneumonia has on growth and future productivity of dairy calves, early identification and treatment are important, but resolution of significant risk factors is imperative! Calves that develop chronic pneumonia seldom recover completely and should be culled. Early vaccination is not an effective means of prevention.
The first three agents listed are the most important in the young dairy calf. Frequently pneumonia is first recognized right after weaning when calves are grouped for the first time. In many herds, the first episode that occurs prior to weaning and as early as 2 weeks of age is missed. In large herds or groups of calves, ear infections can be a sequella to respiratory disease and are frequently caused by the same agents.
Even though the immune system of a calf is functional at birth, it is less responsive than that of an adult cow and is naive and easily overwhelmed by the bacteria, viruses, or parasites in the environment. Prolonged exposure or an increased level of exposure occurs when susceptible dairy calves remain in the calving area, have continued contact with adult cattle, are in contact with affected calves, commingle with sick cows, or are housed in facilities that are under-bedded, warm, damp, humid, or poorly ventilated. Noxious gases, dusts, and molds in the air put calves at significant risk for developing pneumonia. Cold housing can reduce the risk of infection, provided calves can be dry and draft-free. Calf-to-calf contact, crowding, or continuous use of facilities prolongs the survival rate and increases the numbers of pathogens in the environment of the calf, even with cold housing.
Inadequate colostrum intake or absorption puts calves at significant risk of infection from septicemia, enteritis (diarrhea), or pneumonia. Dairy calves should be hand fed 3 liters (Jerseys, Guernseys, Ayrshires) or 4 liters (Holsteins, Brown Swiss) of colostrum. The entire volume should be from the first milking of a single cow. Colostrum can be delivered in one or two feedings prior to the calf reaching 12 hours of age. The entire volume can be delivered safely and effectively in a single feeding. Calves can suckle, be fed by esophageal feeder, or receive colostrum by a combination of the two methods.
Colostrum should be collected from appropriately prepared cows within 6 hours of freshening. Collection and storage containers should be sanitized between sequential uses. For effective cooling, colostrum should be placed in 2- or 4-liter containers that can be clearly labeled with cow identification and date of collection. Fresh or refrigerated colostrum provides the best combination of antibodies (immunoglobulins), immune cells, other important immune factors (lactoferrin, lysozyme, complement), vitamins, and minerals important to the immune system of the calf. The availability of frozen colostrum allows the producer to discard colostrum from cows with mastitis, bloody milk, diarrhea, or Johnes disease and supplement the colostrum from a first-calf heifer, purchased animals, or incompletely transitioned cows. Refrigerated colostrum should be used within 1 week and frozen colostrum within 1 year of collection. The use of mastitic- or antibiotic-containing waste milk has been related to high mortality rates (Losinger and Heinrichs, 1997). Many producers feed milk replacer to decrease the potential transmission of infectious disease. Colostrum absorption may be compromised in calves born in extreme heat or cold, calves that have difficult deliveries or abnormal gestational length, or those exhibiting respiratory difficulty. Other non-colostral factors that impair immunity of calves are inadequate caloric intake; crude protein deficiency; selenium deficiency; low levels of vitamins A, C, or E; reduced stores of copper, manganese, zinc, or iron; and coccidiosis. Inadequate caloric intake puts calves at risk for disease.
For dairy calves, inappropriate volume, concentration, fat or protein content, mixing, or feeding temperature of milk or milk replacer can compromise the immunity of the calf. Failure to provide fresh water and a palatable calf starter that is supplemented with a coccidiostat and presented in a clean feeder will enhance their susceptibility to disease. Consistent feeding practices (timing, presentation, temperature, and quality of feeds)and personnel and management practices enhance the non-specific immunity of the calf. Make sure that there are adequate feeding utensils to be able to clean and disinfect between uses on sick calves. A dedicated utensil for sick calf use is ideal. This means that there are enough esophageal feeders to dedicate one to each sick calf for that feeding or that day. Contain risk by reducing calf stress. Stress is imposed when calves are asked to adapt to change. Feed changes—colostrum to whole milk to milk replacer, dilute milk replacer to concentrated milk replacer, milk withdrawal and reintroduction—create stress. Each time there is a housing change—maternity pen, warming area, calf hutch, group pen, or transport to a different location—the calf is more susceptible to disease. Depending on timing, amount, and type, vaccinations or medications can impose significant health risk to young calves. Keep things simple for calves. Feed a single, large-volume feeding of colostrum. At the second feeding, begin feeding the milk replacer or milk that will be the mainstay of the calf’s preweaning diet. Feed the liquid feed at a consistent time, temperature, and concentration throughout the preweaning period. Make adjustments in volume or number of feedings for cold temperatures or illness. Provide calf starter within the first week of life.
Move the dairy calf from its calving area, and place it in its permanent preweaning home as soon as possible after birth. Avoid crowding and competition, particularly before, during, and immediately after weaning. Under most circumstances, dairy replacement heifers that receive adequate colostrum from vaccinated dams have little or no need to be vaccinated before weaning.
Persistence of the agents that cause diarrhea, pneumonia, and septicemia in the environment is the major reason for outbreaks of calf problems on the dairy. Usually the source of infection is feces (diarrhea and septicemia)—from normal adult cows into shared housing and calves that are non-immune shedders—or aerosol (respiratory disease pathogens). Occasionally, water, feeding utensils, rodents, birds, pets, or people can be the source of infection for calves. Depending on the time of onset of disease, the most likely source of infection can be identified. Problems that occur within 5 days of birth usually have their source as the dam or the calving environment. After 7 days of age, problems develop from a source in the calf environment. If the source of infection can be identified, it can be diluted or bypassed, using one of these strategies:
Successful treatment protocols for diarrhea and pneumonia depend on early identification of sick calves. These criteria can be used to trigger a treatment intervention:
Supportive care is more valuable than antibiotics. Sick calves must be able to stay clean and dry. Keep it in its own housing area, but put fresh bedding down. Administration of warmed fluids is an effective way to raise body temperature. Make sure fresh water is available at least twice daily. Offer milk/milk replacer at the usual dilution and temperature, but reduce volume (to 1 liter, for example) and feed more frequently (4 times/day, if needed). What liquid feed isn’t consumed, administer by an esophageal feeder that has been cleaned, disinfected, and rinsed between calves. Oral fluids are an effective way to correct dehydration provided that the calf is strong enough to stand and has no abdominal distension. Non-steroidal anti-inflammatory drugs like aspirin, banamine, or ketoprofen can keep calves eating. Supplementation with probiotics may help restore the intestinal environment, especially after antibiotic use. Use antibiotics when they are known to be effective for the problem that is identified. Antibiotic selection should be based on culture of the bacterial organism from the premises or during the outbreak. The veterinarian should advise you on route, dose, and duration of therapy. Responsible use of antibiotics is a must!
In conclusion, the five C’s provide an effective formula for managing the young dairy calf:
While the agents that cause disease are always there and can be extremely important in a disease outbreak, a comfortable, clean calves with good colostrum management, consistent feeding and management practices, and plenty of calories in the diet can be disease free even if they become infected.
Sheila M. McGuirk, DVM, PhD, and Pamela Ruegg, DVM, MPVM
University of Wisconsin-Madison