The neonatal phase of calves is a phase that needs extra care due to newborns’ vulnerability. Enteritis - an inflammation of the intestinal mucosa, resulting mainly in diarrhea - stands out among the conditions that affect animals in this period. Enteritis are responsible for huge losses in cattle breeding, especially in the early stages of rearing. Besides the losses caused by mortality, there are also expenses with veterinarians, treatments and decreased performance of the animal throughout its productive life. The present study aimed to perform a review of diarrhea in newborn calves.
The neonatal period in cattle - that goes from birth to 28 days of age - is especially important from a health point of view, since approximately 75% of losses in young calves occur in this phase , and the first week of life is considered the most critical phase, with 50% of losses. Therefore, maintaining the health of calves is highly related to the hygiene of the place where they live, as they are extremely sensitive to environmental pathogens . Lorenz  report that there are several measures to maintain calf health from birth to weaning, including the provision of good quality colostrum in adequate quantity in the first hours after birth and the need to emphasize the prevention of diseases of the gastrointestinal tract and respiratory system. Among the main conditions that cause loss in the early stages of calves development are pneumonia, malformations, central nervous system diseases, and enteritis . Enteritis is clinically mainly manifested by diarrhea and stands out due to its high mortality rate [2,3,5,6], since it is commonly difficult to recover because it is almost always accompanied by malnutrition .
Diarrhea is a complex multifactorial disease involving animal, environmental, nutritional, and infectious agents and it is a major cause of mortality, morbidity, and economic loss in cattle worldwide , because the treatment of affected calves is slow and impacts on growth, weight gain to weaning and loss of genetic potential of recovered animals . Due its clinical and economic importance and due the preventive measures are often
neglected, it is necessary an approach on this subject, to broaden the knowledge and to promote a better conduct regarding the prevention, diagnosis and treatment of the affected animals. Therefore, the present study aimed to review diarrhea in newborn calves.
Newborn calf diarrhea is a disease of great impact on the economic viability of cattle herds worldwide  (Table 1). The economic impact caused by this condition is significant, although many new intervention strategies, such as vaccine development drug development and herd management, have been developed
and implemented to minimize it . In this sense, the veterinarian
needs to assess the status of immunoglobulins in calves, feeding,
shelter, environmental disinfection, hygiene and sanitary
management, to prevent neonatal deaths caused by the disease
. The processes involved in the pathophysiology of diarrhea
are related to intestinal secretion/ hypersecretion, nutrient bad
absorption and digestion, osmolarity, abnormal intestinal motility,
increased hydrostatic pressure, and gastrointestinal inflammation
[12-21], which may occur singly or, more commonly, by the
combination of two or more factors of these mechanisms [22,23].
Secretory diarrheas occur due to abnormal stimuli to the
intestinal mucosa crypts that may be caused by the action of
enterotoxins and/ or the action of inflammation mediators such as
prostaglandins, causing an imbalance in physiological processes,
like secretion and intestinal resorption, with consequent diarrhea
. Diarrhea is typically profuse without blood or effort, and signs
in affected calves include depression, weakness, and sometimes
shock and death secondary to hypovolemia and mild acidemia
. The difference in osmolarity with increased concentration of
solutes within the intestinal lumen, promotes greater absorption
of water by the lumen, thus resulting in dehydration of the
animal. Osmotic particles include poorly digested disaccharides
and increased levels of D-lactate from bacterial fermentation
of unabsorbed nutrients entering the colon. Reduced intestinal
transit time can lead to poor digestion and malabsorption due to
inadequate time for digestion and absorption of ingested food,
impaired fluid resorption has a major impact on fluid balance .
When a calf has diarrhea, there is a huge loss of fluids and
electrolytes from its body. Thus, the consequent dehydration and
the appearance of metabolic acidosis are the main causes of death
of these animals . This happens partly because the evaluation
of the animal is generally based only on clinical examination, and
a more detailed approach to assessing the degree of electrolyte
disturbance and acidosis through blood gas analysis is lacking
or not . Although this condition being common in rural
properties, treatment is usually inadequate and / or insufficient,
because the administration of antibiotics and anti-inflammatory
drugs do not correct the hydroelectrolytic disorders and acid-base
. Therefore, in order for the recovering of the animal, these
parameters must be measured and corrected quickly, enabling the
return to homeostasis. The high frequency and persistence of calf
neonatal diarrhea has attracted the interest of many researchers.
The multifactorial etiology (bacteria, viruses and protozoa)
influenced by nutritional and environmental factors, as well as
difficulties in the precise diagnosis of the agent and the failure of
treatment has required the adoption of prophylactic measures,
such as cow hygiene, management and vaccination .
Diarrhea is a condition of complex multifactorial etiology,
influenced by infectious, nutritional and environmental factors,
as well as improper management practices. Causes include toxins,
bacteria, protozoa, viruses, and management / environmental
factors such as overfeeding, low temperature, poor hygiene,
colostrum deprivation, and individual susceptibility of the animal
. Numerous infectious agents have been implicated in diarrhea
of calves, such as Escherichia coli, Salmonella spp., Cryptosporidium
spp., Rotavirus and coronavirus. Coinfection is commonly seen
in diarrheal calves, although a single primary pathogen may
be the cause in some cases. The non-infectious causes of origin
are related to improper management and poor hygiene of the
environment in which the animals are placed. The incidence of
the disease may vary according to the geographical location of the
farms, farm management practices and herd size . Rotaviruses,
coronaviruses and cryptosporides, the most commonly recognized
enteric pathogens of calves, all produce intestinal villi atrophy,
intestinal bacterial overgrowth, malabsorption, and osmotic
In general, infections caused by viruses and protozoans tend
to damage the intestinal mucosa promoting alteration in intestinal
absorption due to damage to intestinal cells, compromising the
normal absorption of nutrients, fluids and electrolytes, without
alteration in intestinal secretion . Rotaviruses are the most
common cause of diarrhea in newborn calves and are often
involved in co-infections with other agents [11,23,25]. Clinical
signs usually appear 1 to 3 days after infection lasting 5 to 9 days
. High environmental contamination, herds with high numbers
of animals and management that favors the transmission of the
agent, associated with an inexpressive immunization rate, provide
favorable conditions for the spread of rotavirus in dairy herds
in Brazil, justifying the prevalence and difficulty to control the
infection and the spread of the virus . The incidence of many
etiological agents varies with the calf’s age (Table 2) and this is
useful for establishing the probability of a particular agent being
involved and it is generally impossible to establish a definitive
field diagnosis .
Diarrhea may result from hypersecretion or decreased
absorption. Enteropathogenic strains of E. coli are occasionally
causing diarrhea in calves . Enterotoxigenic E. coli, Salmonella spp, Campylobacter spp. and rotavirus cause diarrhea by secreting
enterotoxins that stimulate increased intestinal secretions, while
protozoa and enteric viruses cause epithelial destruction of the
absorptive cell villi. Enterotoxigenic E. coli produces profuse
watery diarrhea, mainly in calves older than 4 days of age and
occasionally in older calves. The F5 antigen may produce a mild
clinical syndrome characterized by diarrhea, dehydration and
weakness in calves from 1 to 4 days of age with rapid course
and may progress from healthy to decubitus and death from 6 to
12 hours . Salmonella spp. is an important causative agent
of diarrhea and septicemia in dairy calves and the depression
caused in the animal is probably due in part to endotoxemia,
not just dehydration and acidosis. Campylobacter jejuni and
Campylobacter fecalis are believed to be of minor importance in
calves and lambs .
Cryptosporidium is cited as the main agent of diarrhea in
calves, not only as an opportunistic agent, but also as a primary
agent. Preventive measures should be taken related to the
management of cows at the time of giving birth, avoiding the
agglomeration of animals and environmental contamination to
reduce economic losses, and to avoid the risks to public health
arising from infection . The recognition of enteropathogens
guides the adoption of effective prevention and control measures,
besides alerting to public health reflexes, due to the zoonotic
potential of several of these enteric pathogens [29,30].
Physical examination of the diarrheal calf comprises the
first step in establishing the therapeutic approach, requiring
the determination of the presence of any intercurrent disease.
Treatment of simple cases depends on the estimative of dehydration
(Table 3), severity of acidosis, likelihood of concomitant infection,
presence or absence of hypothermia and hypoglycemia . The
most common causes of death are dehydration and acidosis. Blood
gas analysis will accurately determine the degree of metabolic
acidosis  (Table 4). Therefore, the immediate goal in treating
depressed calves is to restore them to physiological systemic
status. The estimated severity of dehydration can be combined
with estimates of diarrhea loss and maintenance of essential
functions to manage total daily fluid requirement [11,29].
Abbreviations: pCO2, carbon dioxide pressure; pO2, oxygen
pressure; HCO3-, plasma bicarbonate concentration; TCO2,
total carbon dioxide in plasma; BE, base excess in the blood;
StB, standard bicarbonate blood concentration; SatO2, blood
oxygen saturation. Fonte: Lisbôa et al. . Replacement may be
administered intravenously or orally, reminding that for the latter
one should be increased by 60 to 80% for partial fluid absorption
[11,29]. If performed early in the disease, oral replacement can be
highly effective and inexpensive. In animals with severely impaired
intestinal motility, the intravenous way may be more effective in
correcting hydroelectrolytic imbalances than oral administration
. Success of therapy is monitored based on clinical signs of
calf and restoration of urination . Another point to consider
in chronically diarrheal calf is the need for nutritional support.
When a samll quantity of milk or solid food is ingested, energyrich
oral electrolytes may be used to maintain the body condition
of the animal. Stop giving milk can reduce the severity of diarrhea
and depression in severe diarrhea, because malabsorption
exacerbates diarrhea by the osmotic effect of unabsorbed milk
nutrients and also promotes bacterial proliferation and possibly
poor fermentation generating organic acids. However, stop giving
milk reduces weight gain .
Antibiotic use is frequent in the treatment of diarrhea, although
few agents respond to antimicrobials, viral and parasitic agents
are not directly sensitive to antibiotics. Their indiscriminate use
promotes the selection of resistant strains and complicates future
therapeutic efforts. However, they can attenuate clinical disease,
decrease the release of pathogens to the environment and animal
mortality [11,29]. Some treatment protocols include the use of
anti-inflammatory drugs to help reduce the secretory effects of
some agents . The use of non-steroidal anti-inflammatory
drugs (NSAIDs) should be restricted in dehydrated animals and
administered only when the patient is sufficiently hydrated .
The use of probiotics, oligosaccharides and intestinal protectors
is also cited, and the use of gastrointestinal motility modifiers
is contraindicated, as the reduction in motility will lead to the
accumulation of bacteria and pathogenic toxins .
The principles of prevention are based on ensuring adequate
colostral intake, specific help and nonspecific immunity, reduction
of the possibility of introduction / dissemination of infectious
agents . Colostrum is important in preventing morbidity and
mortality of diarrheal calves. Colostral antibody is responsible for
the low incidence of rotavirus infections in calves under 4 days
of age. Vaccination of pregnant cows is important to increase
colostral immunity. Colostrum privation, lack of maternal instinct,
and early separation of cow and calf are major causes of failure
to transfer immunity in dairy calves . Prophylactic measures
include separating calves from each other with enough space to
prevent contact and infection through contaminated feces and
urine. All feeding facilities and equipment (buckets and bottles)
must be maintained with strict hygiene conditions. There is not
much difference between the patterns of disease development and
the prevention of calf diarrhea according to each etiological agent.
Knowledge of the causal pathogen (s) is important to accurately
avaliate the current status of the affected property and to develop
new interventions .
Diarrhea in newborn calves is a complex disease involving
animal, environmental, nutritional and infectious agents that is
of great clinical and economic importance for ruminant breeding,
especially for dairy cattle. It is responsible for significant economic
losses related to reduced productivity, treatment costs, growth
retardation, discard of future breeders and death of animals in
more severe cases. Care of calves should be considered even before
birth (vaccination of pregnant cows), and maintained after birth,
with the provision of quality colostrum in adequated quantity,
hygiene of facilities and utensils, early diagnosis and treatment
thus avoiding fatal cases
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