Calf Diarrhea Outbreaks in Dairy Herds: Guidelines for Consulting with Herd
Managers
The following article outlines some guidelines we recommend for
evaluating calf diarrhea outbreaks.
Clinical syndrome
Careful monitoring of calves during their
neonatal period
(1-28 days) reveals that most of them--even in purportedly low morbidity
farms--experience at least one bout of loose stools. Therefore, the severity
of individual cases as well as the percentage of the population affected
must be considered in deciding if the herd has a diarrhea problem. A
diarrhea problem exists if, over any continuous one month period, > 20% of
calves are observed to be clinically affected with a diarrheal syndrome that
results in partial or complete anorexia, reluctance or inability to stand,
and/or dehydration. Three major types of outbreaks are recognized.
- Very watery diarrhea beginning in the first 2 days of life. This syndrome is
associated with enterotoxigenic E. coli (ETEC).
- Pasty to liquid diarrhea, often foul smelling and gaseous, with a peak
during the 2nd and 3rd weeks of life (7-21 days of age). This syndrome is
associated with several viral agents and Cryptosporidium.
- Pasty to liquid diarrhea, sometimes with blood, most commonly beginning in
the second or third week of life and usually extending into post-weaning
groups. Accompanied by signs of bacteremia in some of the cases. This
syndrome is associated with Salmonella spp.
Epidemiology of agents
Most of the agents of calf diarrhea exist in
every
cattle herd, the major exception being Salmonella. For agents such as
cryptosporidium, rotavirus, and coronavirus, infection is near-universal
(all calves on all farms) at some time during the neonatal period (1-28 days
of age). Thus, efforts to identify these agents provide little or no
diagnostic utility in that one would expect to find one or more of these
agents in over half of calves (healthy or sick) sampled between 7 and 21
days of age, even in a herd not experiencing a problem with calf diarrhea.
Goal of consultation
To determine the management factors which need
to be
adjusted in order to minimize exposure doses of ubiquitous agents, to
minimize probability of exposure for epidemic agents (i.e., Salmonella), and
to increase calf resistance. The main areas of concern are: passive
transfer, nutrition, housing, and infection control. A brief synopsis
follows which lists the details which should be examined in each of these
major areas.
Passive Transfer
ASSESSMENT: The only reliable means of assessing passive transfer management
is to take blood samples from calves and measure the passive immune levels
of groups of calves. Questioning management about policies, though
important, will not give an accurate picture of passive transfer.
TEST: The easiest test for passive transfer is total serum protein by refractometry. Calves should be at least 24 hours old and under 7 days old
when sampled. All calves available in this age range should be sampled. In a
herd with optimum management of passive transfer, >90% of calves should have
TP of 5.0 g/dl or greater (corresponds roughly to 10 mg/ml IgG1). The
occurrence of any calves with TP of < 4.5 g/dl is a clear indication of
failure to properly feed colostrum.
FORCE FED: All dairy calves should be force fed colostrum. A stomach tube or
esophageal feeder is the only practical way of feeding an adequate volume
under most conditions.
AMOUNT: Holsteins should be force fed 1 gallon of colostrum; Jerseys 3
quarts.
TIME: Force feeding should occur within 8 hours of birth; within 4 hours is
ideal but difficult to achieve on some dairies.
WHICH COLOSTRUM: Only first milking colostrum should be used. The
traditional practice of saving only colostrum from older cows places
unnecessary constraints on the program since colostrum from first parity
animals does not differ notably in IgG concentration from that of older
cows. Indeed, the colostrum from older cows which give high volumes in their
first milking is the more predictably low in IgG than is colostrum from
heifers.
COLOSTRUM TESTS: Tests based on specific gravity only modestly correlate
with IgG concentration (r~.5). If an adequate colostrum feeding program is
in place (1 gallon, 1st milking colostrum, tube fed to every calf within 8
hours), testing colostrum and discarding those with low test results will
not significantly improve the passive transfer results achieved.
STORAGE: Colostrum should not be stored at room temperature as it will
provide a medium for tremendous bacterial growth. Storage in a refrigerator
is ideal; colostrum which is collected in a clean manner (in parlor under
normal milking conditions) can be kept for a week in the refrigerator.
Freezing is also acceptable, though the time required for thawing
discourages proper feeding of calves.
COLOSTRUM SUPPLEMENTS: Powdered colostrum supplements are very expensive,
particularly considered in terms of cost per gram of circulating IgG1
delivered to the calf. We are unaware of any product which is able to
regularly achieve even a moderately high passive immune level (greater 10
mg/ml IgG1) at the amounts which are recommended and affordable. It is
noteworthy that proper feeding of colostrum will almost always achieve this
level.
Nutrition
LIQUID DIET CALORIES: Calves should receive a liquid diet that at least
meets their maintenance energy requirement (see Tables 1 and 2). If waste
milk is diluted (e.g., with hot water to warm it up), one must consider only
the original (undiluted) volume fed to the calf in figuring caloric
adequacy. Calves fed less than maintenance will lose weight for the first
week or two of life and will be more readily put into an energy crisis by
the anorexia and malabsorption of diarrheal disease. Calves in a negative
energy balance are also more susceptible to the effects of rapid temperature
changes (e.g., a cold front).
MILK REPLACER. Only all milk-protein milk replacers should be fed to calves
< 2 weeks of age. Though, in theory proteins from whey byproducts may not be
as digestible as those from skim milk or casein products, calves generally
do well on milk replacers containing most of the protein from whey products.
GRAIN FEEDING: Calves should be offered grain at some point beginning in the
first week of life. Calf grain should contain at least 16% protein and
should consist of whole or rolled grain along with a protein pellet. Grain
mixes made for cows should not be used for calf feeding. For new calves only
a handful of grain per day should be offered, and the residue should be
discarded at least as often as every third day. One common mistake in
feeding calves is to continue to add new grain onto the top of old grain,
gradually filling the bucket with stale, moist, mold-infested, bacteria-rich
grain. Calves are reluctant to eat this mess and will thus have reduced
gains. To the extent they do eat it, gastrointestinal disturbances can
result.
WATER: Ideally calves will have clean water in front of them all the time.
Calves can make up for some of their fluid losses from diarrhea by
increasing voluntary water intake. Also, the lack of supplemental water will
reduce grain intake. Provision for round-the-clock access to water is
impossible in the winter months in cold housing (e.g., hutches). During
freezing weather, a small amount of water (1 quart) can be placed in each
calf's bucket between feedings; remaining water is dumped 30 minutes to 1
hour later before it freezes solidly.
HAY: Calves pre-weaning and grouping need not be offered hay. Ruminal
papillary development will proceed normally for calves fed only grain.
SELENIUM: In the dairy producing areas of the Pacific NW (and most of the
US), calves should be given selenium injections within 3 days of birth
unless testing of calves has demonstrated that they are not deficient.
Housing
ENCLOSED HOUSING: Where calves are confined in an enclosed space,
agent-laden aerosols can settle out on calves haircoats and onto feed and
utensils, and can thus be ingested. This provides an additional--difficult
to control--means of transmission that is not experienced by calves in
hutches and in properly managed naturally ventilated structures. The
ventilation system of an enclosed barn influences aerosol transmission by
direct removal of agents and by lowering humidity which in turn decreases
survival time of (some) agents. Assessment of ventilation adequacy of
enclosed barns consists broadly of measuring airflow per calf (e.g., summer
requirement of 100 ft3/calf/min) and evaluating airflow patterns (drafts and
dead spots). The subject is too extensive to cover in detail here, though it
can be said that few enclosed barns in the Pacific NW have been found to be
adequately ventilated and that this likely plays a major role in the
perpetual diarrheal and respiratory disease suffered by the occupants of
such buildings. For more details on evaluating ventilation of enclosed
housing, call Dale Hancock (509-335-0711).
HUTCHES: Though hutches are an ideal method of housing calves, several
important details must be examined.
Hutches should be tight to the ground--no slats or cracks through which wind
can blow onto calf from underneath.
Open end of hutches should be south- or south-east facing during cold
months, and the other three walls should be solid with no openings.
The portion of the hutch which is completely enclosed on three sides should
be of sufficient depth to keep calves out of wind and drifting snow--6 feet
is ideal.
Hutch design should provide for upward air drainage; body heat will make air
rise in winter, and moisture will accumulate unless roof is single-sloped
upward toward opening or unless a vent is located at the highest point of
hutch ceiling.
Substrate should provide for adequate liquid (urine, etc) drainage from the
hutch; 4 inches or more of crushed rock is an ideal substrate.
Bedding should provide for adequate thermal insulation--straw is preferred
over shavings in winter. Additional bedding should be added weekly; old
bedding should be removed only after calves are weaned and moved out.
NATURALLY VENTILATED BARNS: Naturally ventilated barns are those for which
there is no mechanical ventilation system and in which no attempt is made to
warm the air above outside temperature. Calves are kept in stalls or
tethered, and are bedded during cold weather. The adequacy of naturally
ventilated housing depends on the natural air purification produced by body
heat- and wind-driven air flow and diffusion through openings. The adequacy
can be assessed by comparing the design to specifications for opening size
and positions found in a farm animal housing publication (e.g., Dairy
Housing and Equipment Handbook, Midwest Plan Service, Iowa State University,
Ames 50011, 1985). For example, one major design type requires a ridge vent;
specific requirements for width of the ridge vent can be determined from
building dimensions. One can also assess adequacy of air movement by
measuring carbon dioxide concentration in the calf barn on a still day; if
it is much above atmospheric levels, the natural air purification created by
the structural design and operation is not adequate. For more details,
contact Dale Hancock (509-335-0711).
POST-WEANING GROUPING OF CALVES: Calves should be weaned while they are
still in individual housing and a least 5 days before they are moved into
group housing. The group pen into which calves are first moved should have
the following characteristics: no more than 10 calves, no more than 2 months
in age difference among calves in group, and at least 1 foot of feed bunk
space per calf. Putting newly weaned calves into large groups of mixed ages
with inadequate bunk space will result in a period of high stress and
reduced caloric intake of newly weaned calves.
Infection Control
FEEDING UTENSILS: If nipples or buckets are shared by multiple calves during
a feeding (that is, there are not as many nipples as calves to be fed), they
must be disinfected between calves. A common mistake is to use a dairy
chlorine sanitizer for this; while such a product is acceptable for
sanitizing equipment that is completely clean, the milk residue left on
nipples during feeding will inactivate the chlorine, which result in an
ineffective disinfection. Ideally, enough nipples or buckets will be
purchased to avoid sharing during feedings. Alternatively, chlorhexidine
(3oz/gal) can be used for disinfection during feeding.
TREATMENT UTENSILS: The infection and clinical thresholds (amount of an
agent required to infect and to produce clinical disease) are lowered for a
sick calf, hence care should be taken in sanitizing treatment
equipment--especially those instruments, such as balling guns and stomach
tubes, which go into the calf's mouth. The use of a common esophageal feeder
for tubing newborn calves with colostrum and sick calves with fluids is
strongly discouraged. Chlorhexidine (3oz/gallon) is an effective
disinfectant for treatment equipment.
CALF PENS: In most operations, a complete disinfection of calf pens between
every use is difficult and is not necessary. For example, hutches cannot be
adequately cleaned and disinfected during freezing weather. At least a
couple of times per year, however, pens should be washed with a high
pressure sprayer and then disinfected with a phenolic disinfectant (e.g.,
Environ) mixed per label instructions. Other disinfectants (chlorines,
chlorhexidine, quats) are not as effective as phenolics for environmental
decontamination and tend to be more expensive. Prior to use of high pressure
sprayers, enclosed barns must be emptied completely of calves.
DISCARDED CALF GRAIN: Leftover grain from individual calf buckets should not
be fed to other calves in individual housing nor to any calf under 6 months
of age.
CALF GRAIN STORAGE: Grain can be stored for short periods (less than 2
weeks) in bags; longer periods of on-farm storage in bags can result in
heavy rodent infestations and the possible contamination with Salmonella.
Rodents can carry a variety of Salmonella serotypes, including S. dublin.
Grain delivered in bulk should be put into a metal bin from which it is
electrically augered rather than into a walk-in room. It is very difficult
to use a walk-in grain room without risking Salmoenlla contamination of
grain, and walk-in grain rooms tend to be feeding stations for rodents.
RUNTS AND CHRONICS: Some chronic salmonellosis cases can carry the offending
Salmonella organism for periods of up to a month or more. Many of these
calves tend to be runts, and the tendency in group pens is to house them
with a younger set of calves which may be more similar in size. This
"bumping back" of runts and chronics is not desirable from the standpoint of
infection control.
Last revision 7/2/97
