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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
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