CONTROL OF INFECTIOUS REPRODUCTIVE
DISEASE: THE ROLE OF BIOSECURITY
Russ Daly, DVM
Veterinary Science Department
Many conditions affect the reproductive health of the
beef herd, including nutrition, bull fertility, and environmental
stresses. Perhaps none have the
potential to create more significant losses than infectious diseases. Infectious diseases affecting reproduction
can create losses all throughout the reproductive cycle by decreasing ovulation
rates, fertilization rates, embryonic survival rates, and fetal survival
rates.
How an infectious disease manifests itself in an animal
population is the result of the interaction of three different factors: 1) the
host; 2) the infectious agent; and 3) the environment. This is referred to as the “epidemiologic
triad” (Figure 1). Management practices
(or lack of them) will influence all three of these factors. A common mistake
is to focus on only one part of the triad.
For example, trying to boost the host’s resistance to a disease by
vaccination without paying attention to the sources of and exposure to the
agent or the environment in which the host and agent coexist, will result in
less than effective suppression of the effects of the disease. Attention must
be paid to all three aspects of the condition in order to maintain herd
health. Reproductive diseases are no
different than others in this regard.
One
management concept that affects the interaction between the host, agent, and
environment is that of biosecurity. Simply put, biosecurity may be defined as
procedures implemented to keep novel infectious agents out of a population (for
example, a cow herd).
Reproductive diseases pose special challenges. Identifying specific reproductive pathogens
is usually difficult. Causes of
abortion, in particular, are very difficult to consistently diagnose. Roughly only a third of abortions submitted
to diagnostic laboratories are diagnosed as due to a specific cause, not all of
which are infectious. Infertility through decreased conception rates or early
embryonic death is similarly difficult to diagnose, in part because effects of
infectious reproductive disease are not always readily apparent. In most cases, a problem is not identified
until pregnancy-check time, well after the inciting agent has left the
reproductive tract, and sub-fertile bulls may recover enough by the time an
investigatory breeding soundness examination is performed.
For all of these reasons, it is much more economical and
sensible to institute biosecurity procedures in order to keep out infectious
disease, rather than try to diagnose and then deal with a problem after the
agents have entered the herd.
This paper and presentation will cover six important
reproductive diseases: bovine viral diarrhea (BVD), infectious bovine
rhinotracheitis (IBR), leptospirosis, vibriosis, trichomoniasis, and
neosporosis. What follows is not a
comprehensive discussion of all aspects of the diseases; rather they will be
examined in the context of how biosecurity procedures can be implemented to
keep them out of a clean existing herd.
Biosecurity programs have four major components:
1. Diligent
homework about the source of the animals.
Before animals enter the farm or are purchased, information about the
source herd should be obtained. Data
regarding source herd testing procedures, health programs, and biosecurity
programs are valuable pieces of information even before the animals are
purchased. Granted, there are many
situations in which this information is not available (purchases at livestock
markets, etc.).
Herd-level testing for an infectious disease is not
necessarily a guarantee that the specific animals purchased will be
disease-free; however, it creates a higher level of assuredness compared to a
similar herd without disease surveillance in place. In some cases, in which individual animal
tests lack sensitivity, whole-herd tests may be of more value than tests on the
individually purchased animal.
Reputable producers will be straight-forward and open
about the health status of their herd and animals. Some may agree to pre-purchase diagnostic
testing; some may provide the name of their veterinarian so that the
veterinarian of the receiving herd can communicate with them regarding herd
health and proper methods of introducing the new animals.
Perhaps one of the best indicators of lack of infectious
reproductive disease in a source herd would be that of a history of consistent
excellent reproductive performance (pregnancy rates, calving rates). Demonstrable evidence of vaccination and
biosecurity procedures would also be pieces of evidence that would be favorable
to the health potential of the source herd’s animals.
2. Isolation/Quarantine
and Testing. By far, the most common
way that new infectious agents enter a herd is through introduction of infected
animals. By preventing immediate contact
between affected and non-affected animals, we allow entering animals an
opportunity to recover from any transient illnesses that they may be incubating
on or shortly after arrival. For many
conditions, this helps to ensure that new animals do not shed these infectious
agents to animals in the existing herd.
This is especially important in the case of animals stressed by
shipping, which have a greater likelihood of succumbing to conditions such as
bovine respiratory disease complex (BRDC) due to the immune-suppressant effects
of stress. Likewise, this isolation
allows the incoming animals to be protected from sudden exposure to agents from
the existing herd at a time when stress makes them more susceptible.
It is important to realize that for certain conditions, any
length of isolation period is not sufficient for animals to cease their
shedding of some infectious agents. For
example, cattle persistently infected with BVD will shed virus throughout their
lifetime. Likewise, cows infected with
host-adapted strains of Leptospira
will shed organisms persistently, too.
In general terms, for transient diseases such as many of
the BRDC agents and infectious bovine keratoconjunctivitis (IBK, or “pinkeye”),
a 30-60 day isolation period is considered sufficient.
Characteristics of an effective isolation site include:
a) Physical separation from
existing herd members. At best, the
isolation facility would be sited as far from the existing herd as possible,
ideally at another farm site. At a
minimum, the isolation site should not allow nose-to-nose contact from new to
existing animals. Most BRDC pathogens
such as IBR, BRSV, Haemophilus somnus,
and Mycoplasma bovis, among others,
do not survive for long periods outside the host, and require close contact for
transmission to occur. However,
providing maximal physical separation will best ensure that aerosol
transmission of pathogens does not occur.
b) Separate runoff and drainage
patterns. Pathogens transmitted
through feces (BVD, Salmonella) or
urine (Leptospira) could potentially
infect either the new arrivals or the existing herd if manure runoff or
drainage enters the other site, despite a producer’s best efforts to provide
nose-to-nose separation between the groups.
c) Management
such that equipment and instruments are
not shared between groups. Any
equipment that enters a lot such as tractors, trucks, or skid-steer loaders
that need to enter a lot to feed or move manure, should only be used in one
place or the other. Alternatively,
equipment tires and loader buckets, etc. could be thoroughly cleaned and
disinfected between groups. Equipment such as stomach tubes, oral bolus guns,
tube feeders, etc. should be restricted to either the isolation site or the existing
herd and not shared between groups.
Boots and coveralls used by personnel entering the lots or contacting
the animals should be changed between groups.
d) Testing of new arrivals.
The isolation period is the time in which incoming animals should undergo
testing for certain diseases, depending on the disease and the producer’s
goals. Specific recommendations for
testing will be outlined separately for each disease later. For some diseases, limitations in diagnostic
test sensitivity are present. For
example, for Johne’s disease (an important non-reproductive disease which will
not be discussed in this paper), the commonly used serum ELISA test has a
sensitivity of only about 15% in non-clinical cases. For this disease, therefore, herd-level
testing of the source herd is more valuable than individual blood tests for
detecting potentially infected animals.
In any event, diagnostic testing of incoming animals should
not be done indiscriminately. There
should be a prior understanding of the limitations of testing and of what
interventions will be employed if unexpected test results occur. If animals are kept and allowed to enter the
herd despite positive test results, diagnostic testing is a waste of time and
resources. No animals should be allowed
to enter a herd from isolation until they are confirmed negative to a disease
of interest, as determined by the producer and their veterinarian.
e) Vaccination/Acclimation of
the new animals. The isolation
period should also be used to coordinate the immune status (through use of
vaccination) of the newly arrived animals with that of the existing herd. The timing of vaccine administration to these
animals should be carefully considered in light of: confirmed previous vaccinations before
arrival, stress level of the new arrivals, and possible interference with
diagnostic testing (diagnostic tests based on blood antibody levels will likely
be affected by vaccination, creating potential for false positive test results).
A practice seeming to gain favor is that of vaccinating
incoming cattle with an intranasal MLV (modified live virus) IBR-PI3 vaccine on
arrival or before they leave isolation.
This vaccine can be administered safely to stressed or pregnant animals
and is considered by some to provide rapid mucosal immunity (resistance
centered on the lining of the nasal passages and upper respiratory tract) to
the animal.
3. Vaccination/Treatments. Another component of biosecurity involves
increasing the herd levels of resistance through proper vaccination. It is important to realize that vaccination
of all individuals within a population does not mean that each individual
becomes immune to the agent in question.
Individual animal responses to vaccine are subject to biological
variation, in which a few animals respond extremely well to the vaccine, a few
respond poorly to the vaccine, and most animals respond in an intermediate
fashion.
Therefore, the goal of a vaccination program is not to
render each individual immune to disease; rather it is to stimulate sufficient
immunity in a sufficient number of animals such that an epidemic, or widespread
outbreak, does not occur.
Herd vaccination programs should be considered a form of
risk management rather than a means to completely prevent disease. Differences between vaccine strains and wild
virus strains, or overwhelming exposures to pathogens are both reasons in which
even a well-vaccinated herd can express significant clinical disease. All vaccine programs should be designed with
appropriate guidance from a veterinarian.
For certain diseases, antibiotic treatments are indicated
when animals enter isolation. For
example, injections of long-acting tetracycline are used to clear cows or
heifers of the carrier state of leptospirosis.
Otherwise, blanket antibiotic treatment without an underlying reason is
probably unnecessary for healthy incoming cattle.
4. Environmental
Control. As will be described later,
for certain diseases, control of environmental factors is important in
controlling disease transmission.
Environmental factors may influence the relative ease with which disease
agents are transmitted and may influence the resistance of the animals to
clinical disease. Other disease agents
(IBR, Campylobacter, and Tritrichomonas do not survive outside
the host animal for long periods of time, and environmental control is not an
issue in prevention of these diseases.
Infectious Diseases Affecting
Reproduction: Specific Biosecurity Aspects
Bovine Viral Diarrhea (BVD) virus
Evidence of exposure to BVD virus is widespread
throughout cattle herds in the
BVD virus is spread through many body fluids including
saliva, respiratory secretions, and feces.
The virus does not persist in the environment but can survive long
enough to be transmitted via infected equipment, needles, and palpation
sleeves.
Persistently infected animals are especially efficient at
transmitting virus, since they shed a tremendous number of viral particles. These animals can effectively infect
susceptible animals through brief (as short as one hour) nose-to-nose or
fenceline contact, and can shed enough virus to overwhelm a proper vaccination
protocol. When on pasture during the
breeding season, they can efficiently cause the creation of more PI calves by
infecting cows in the right stage of gestation.
Identification of persistently infected calves can be
accomplished with various diagnostic techniques. Perhaps the most effective is that of using
an ear-notch from the calf in an ELISA test.
This results in a yes-or-no answer and is generally extremely reliable
in identifying persistently infected calves.
·
Isolation/Quarantine
and Testing. As previously mentioned, if an animal is
persistently infected with BVD, no length of isolation period will be long
enough. A 30-60 day isolation period will,
however, allow any transiently infected animals to clear their infections
before contacting the existing herd.
Some seedstock producers are now marketing
animals as “PI-test negative.” As the
term implies, this is not 100% proof that an animal is not PI (since no
diagnostic test is 100% sensitive), but is as good an assurance as can be made.
If not previously performed, proper testing for BVD PI animals is critical
during the isolation period. All
incoming animals should be ear-notched upon arrival and the samples tested for
BVD PI. This includes not only purchased
females and bulls, but also offspring of purchased bred animals, since only
rarely is the dam herself persistently infected. Also, any purchased foster calves should be
tested before leaving isolation.
This testing should be performed as soon
as possible, and animals identified as PI promptly removed from the herd. Depending on the animals left in isolation
after PI calf removal, a producer or veterinarian may consider starting the
isolation “clock” again to ensure that any transiently infected animals have a
chance to clear their infections after the source of their infection is removed.
It is usually recommended that a positive
ear-notch test be re-confirmed with another diagnostic method 2-4 weeks
following the initial test. This is due
to the fact that transient infections may give positive results on the ear
notch ELISA. This is an especially
important distinction to make with valuable animals. Depending on timing and the number of calves
involved, a producer may alternatively opt to dispose of all calves testing
positive to the first test.
·
Vaccination. Vaccination
is an important tool in the overall herd biosecurity plan, but, as previously
mentioned, even a proper vaccination program can be insufficient if exposure is
overwhelming.
While in isolation, incoming animals
should be vaccinated to coordinate with the existing herds’ program, if
possible. Common recommendations are for
MLV vaccines used preferably 30 days pre-breeding. BVD, like IBR, is very commonly used in
pre-conditioning programs, which usually enable vaccine given when heifers
reach breeding age to be that much more safe and more effective.
·
Environmental
Control. Proper cleaning and disinfection of
potentially contaminated equipment should be practiced, and sources of runoff
between animal groups should be managed.
Researchers have recently identified deer persistently infected with
BVD, so the role of wildlife in the transmission of BVD warrants further study
and consideration.
Infectious Bovine Rhinotracheitis (IBR, “Red-nose”)
IBR virus is also termed BHV-1, or “bovine herpesvirus
1.” Being a herpes virus (in the same
family as viruses causing cold sores in people), it has a propensity to become
“latent” or dormant in nerve clusters in the throat area or lower spine, and
can re-activate during times of stress.
Because of this, any animal exposed to IBR in the past could potentially
shed the virus to susceptible animals.
IBR is shed and transmitted in nasal secretions and aerosols from
infected animals.
In addition to its effects on the respiratory tract, IBR
virus affects reproduction by its effects on the ovaries, uterus, and
developing embryo or fetus. The result
can be infertility or early embryonic death, but in addition, IBR is one of the
most frequently diagnosed viral causes of late-term (5th to 9th
month of gestation) abortions.
·
Isolation/Quarantine
and Testing. An isolation period for incoming animals
would be considered prudent despite the possibility that animals may be
latently infected with IBR for long periods of time. Any episode of acute shedding of virus or clinical
signs brought on by the stress of transport would die down to a low level
during a 30-60 day isolation period.
Because, like BVD, evidence of exposure to
IBR virus is widespread in North American cattle, testing for IBR while in
isolation would be considered of little use.
·
Vaccination. Vaccination
for IBR is widely practiced and many products are available, either killed or
modified live, most often in conjunction with other viral antigens. They are used in pre-weaning and weaning
vaccination programs in calves, and also in pre-breeding programs for breeding
animals, reflecting its potential to cause both respiratory and reproductive
problems. Vaccine has been effective in
preventing outbreaks of clinical disease, but does not necessarily prevent
infection or eliminate latency.
Currently, modified live vaccines are used
pre-breeding to protect females against IBR abortions and infertility. Safety issues have arisen with the use of
modified live IBR vaccines in seronegative (naïve) heifers close to breeding in
that ovarian lesions and temporary infertility can result. These phenomena have not been reported in
animals that have had proper pre-conditioning (pre-weaning and weaning) IBR
vaccinations.
Safety concerns also arise when MLV IBR
vaccines are given to pregnant animals.
Recently, vaccine label revisions have resulted in the approval of the
use of MLV vaccines in pregnant animals provided they were properly vaccinated
pre-breeding. This practice should only be
undertaken under the strict guidance of a veterinarian with meticulous
attention paid to label directions.
Severe pregnancy losses have resulted when animals of unknown prior
vaccination history have been given MLV reproductive vaccines.
During the isolation period, depending on
the animals in question, it is usually advisable to vaccinate animals in
isolation to coordinate with the rest of the herd. If it is pregnant animals that are isolated,
MLV vaccines should not be given. Producers may consider administering intranasal
MLV IBR-PI3 vaccine to animals before they leave isolation. Intranasal MLV IBR PI3 is safe for pregnant
or stressed animals.
Leptospirosis
Leptospirosis has long been recognized as a cause of
infertility in cattle. Symptoms of Leptospira infection include early
embryonic death (manifested as repeat breeders and reduced pregnancy rates),
late-term (7th to 9th month of gestation) abortions, weak
liveborn calves, and low-grade uterine infections.
Producers and veterinarians for years have vaccinated
cattle for leptospirosis by using a “5-way lepto,” usually in combination with Campylobacter (“Vibrio”) and viral
antigens. These five strains are named Leptospira
Leptospira
hardjo-bovis is referred to as a “host-adapted” strain of Leptospira in cattle. This means it can evade with relative ease
the host’s immune system to create a persistent carrier state in the body. In contrast, cattle are considered
“incidental hosts” for other strains of Leptospira. This means that those strains are
persistently carried in other species (such as dogs, rodents, and raccoons, for
example), and cattle become infected when exposed to strains shed by these
animals.
Leptospira
strains colonize the kidney and reproductive tracts of cattle. The organisms are shed in the urine, and
susceptible animals become infected through contact of their mucous membranes
(eyes, nose, and mouth) with infected urine.
These organisms are hardy in the environment and can be found in contaminated
standing water.
·
Isolation/Quarantine
and Testing. Host-adapted strains of Leptospira colonize susceptible animals such that extremely
long-term shedding will result.
Therefore, an isolation period of any length will not be
sufficient for these animals to stop shedding the bacteria.
Testing individual animals for Leptospira infection is problematic at
best. Testing serum for antibodies or culturing
urine for the bacteria is quite insensitive.
Negative results do not mean the animal is not shedding. Polymerase Chain Reaction (PCR) examination
of urine samples is an extremely sensitive, if expensive, method of diagnosis,
but runs the risk of false positive tests if even a minute amount of urine from
a positive animal contacts the sample.
·
Vaccination/Treatment. Incoming
animals should be given a primary dose of L.
hardjo-bovis vaccine, preferably in conjunction with the multivalent
traditional “5-way” lepto in order to provide protection form the incidental
strains of Leptospira the animals may
encounter. A booster of the L. hardjo-bovis vaccine should be given four
weeks following the primary dose. It is
important to use a vaccine specifically labeled as containing L. hardjo-bovis. These vaccines have demonstrated the ability
to protect animals from kidney colonization and there is evidence that carrier
states in animals are eliminated by vaccination.
In addition, animals entering isolation
should receive a dose of antibiotic to eliminate any potential carrier
states. Long-acting tetracyclines such
as LA-200 or Bio-Mycin 200 are commonly used.
Because of the limitations of diagnostic testing, antibiotic treatment
and vaccination are usually considered the main points of leptospirosis
biosecurity.
·
Environmental
Control. Since Leptospira
can survive for extended periods of time in standing water and runoff,
these sources of infection should be managed as best as possible. Because rodents and wildlife species can
carry Leptospira, efforts to control
these animals’ access to livestock in isolation are important.
Campylobacter fetus subsp. venerealis (“Vibrio”) infection
Vibriosis is a bacterial disease that affects the
reproductive tract of male and female cattle.
Symptoms of vibriosis manifest themselves as infertility (decreased
pregnancy rates and prolonged returns to estrus). Late term abortions are rare. Effects of these bacteria are a result of the
inflammation they cause in the inner lining of the uterus (endometritis).
The causative bacteria is maintained in a group of cattle
by persistently infected bulls which carry the agent in the lining of the
sheath and penis. The infected bull
passes the bacteria to cows or heifers during the act of breeding, after which the
organism colonizes the reproductive tract and causes the resultant inflammation. Cows generally clear the infection after
several months but serve as a source of infection for bulls that breed them. Vibriosis is a relatively infrequently
diagnosed cause of reproductive failure in northern plains beef herds
today. Pockets of infection still exist,
however, and producers should not “let their guard down” against this
disease.
·
Isolation/Quarantine
and Testing. Older (three or more years of age) bulls
carrying vibriosis are likely to carry the organism for life, while younger
bulls (2-3 years of age) have the ability to clear themselves of the
infection. As a result, an isolation
period of 30-60 days may be useful for younger, but not older bulls.
Specialized transport media is necessary
to successfully culture Campylobacter. Current recommendations are for three tests
to be performed at one-week intervals.
Currently, bulls entering bull studs are commonly cultured for Campylobacter but not often in other
commercial conditions. Use of
vaccination and of virgin bulls seem to preclude testing of bulls for Campylobacter at this time.
·
Vaccination
and Treatment. Vaccination has proven quite effective for
control of vibriosis. There are
differences among Campylobacter
vaccines in regard to duration of immunity and whether boosters are required
for initial vaccination. Oil-based
vaccines are labeled for one-dose protection and generally result in a longer
duration of immunity than other products.
Vaccine should be administered relatively close to breeding to maximize its
effectiveness. Bulls and breeding
females should receive one dose of the oil-based vaccine one month prior to
breeding, or two doses of other vibrio vaccines (this includes lepto-vibrio
combinations) two to four weeks apart one month before breeding the first year
and annually thereafter. There is
evidence that vaccination will enable infected bulls to clear themselves of
infection.
Trichomoniasis
Trichomoniasis is a venereal disease caused by a
single-celled protozoon, Tritrichomonas
foetus. Symptoms of this condition
are very similar to those of vibriosis, in part due to the fact that this agent
also causes inflammation of the inner lining of the uterus and of the developing
fetus. Infertility results from early
embryonic loss, which shows up as returns to estrus (both regular and prolonged)
and rarely, abortions.
Transmission of trichomoniasis is also very similar to
that of vibriosis. Bulls, usually older
bulls, are the reservoir and carrier of the protozoa in the herd and transmit
it to cows when they breed them. As in
vibriosis, organisms are carried in the lining of the sheath and penis. In contrast, though, to vibriosis, bulls
rarely clear themselves after they are infected and are considered infected for
life.
·
Isolation/Quarantine
and Testing. Many states, including
Non-virgin bulls should undergo the three
weekly test regimen while they are in isolation if this has not been performed
prior to purchase. Testing three
sequential samples improves the sensitivity of the overall procedure to nearly
99.9%. Special culture pouches with
transport media are necessary for a proper culture.
Since bulls are lifelong carriers, and
cows may carry the agent for a prolonged period of time also, the length of the
isolation period is immaterial.
·
Vaccination. A vaccine is
available for trichomoniasis, but it does not prevent infection in cows nor
does it affect the status of the infected bull.
Its main use is for those herds already infected that are not able to
employ the right management tools to eliminate the disease from the herd. In infected herds, vaccine has been shown to
improve pregnancy rates and decrease the duration that a cow is infected. Routine use in non-infected herds is not
advocated.
Neospora caninum
infection
Infection with the protozoa Neospora caninum has recently become recognized as a not-infrequent
cause of abortion in dairy and beef cattle.
Surveys of dairy and beef herds indicate that exposure to this agent is
relatively widespread, as measured by serum antibody responses.
Abortions due to Neospora
may occur at any stage of gestation, but are most common between five and six
months of gestation. In addition,
stillborn calves or infected liveborn calves may result from this
infection.
Neospora is
considered to have “definitive hosts” and “intermediate hosts.” Cattle are the intermediate hosts for Neospora and dogs, foxes, coyotes, and
other wild canines are the definitive hosts, or reservoirs, in which the
organism is maintained.
Initially, a canine will encounter the protozoa when it
feeds on a dead calf or placental tissue that was infected with N. caninum. The organism forms cysts in the body of the
canine, which are passed out of the body through its feces. If these animals defecate into a feed source,
or in the environment of a cow, the cow may ingest the protozoa. The protozoa then travel through the cow’s
body to the pregnant uterus and infect the developing calf. This infection, if severe enough, will kill
the fetus, causing it to be aborted. The
cycle then starts over when canines have access to the aborted fetus and
tissues.
So cattle can either become infected by ingesting
contaminated feces or, in the case of a liveborn calf, become infected in
utero. These calves, if raised to
breeding age, have a higher likelihood of aborting their first and second
calves also.
·
Isolation/Quarantine
and Testing. When considering isolation of newly-purchased
animals, it is important to realize that infected animals will only transmit disease
to others when they calve (or abort).
Probably of more importance than an isolation period is the practice of
performing diagnostic blood testing during the isolation period to identify
females that should not enter the breeding herd.
Intense control measures would entail
testing the entire breeding female herd and either: 1) identifying positive
animals and not keeping their offspring as replacements (as there is a high likelihood
they will be infected and perpetuate the disease); or 2) culling all positive
females and replacing them with test-negative animals. Considering these options should be done
primarily in the face of significant problems with Neospora and with a close accounting of the economic costs and
benefits.
·
Vaccination. A vaccine for
Neospora is commercially available,
although not widely evaluated in the field.
There is published evidence that use of the vaccine has reduced
prevalence of abortion in significantly affected herds. The vaccine is designed to be given to the
pregnant animal in the first trimester of pregnancy, with a booster three to
four weeks later, and annual (subsequent pregnancies) boosters thereafter.
Use of vaccine will result in antibody
titers to Neospora in vaccinated
animals. Therefore, implementing a
vaccine program before any herd testing will prevent a producer from accurately
identifying carrier cows in a test-and-cull program. Any consideration of vaccination should be
discussed with a veterinarian before implementation.
·
Environmental
Control. Of all the reproductive diseases discussed, neosporosis
is the one condition for which environmental control is the most
important. As outlined by the protozoa’s
life cycle, risks of transmission to unaffected females lie in either: 1) the
contamination of feedstuffs by wild or domestic canines; or 2) the exposure of
canines to infected fetal tissues.
Therefore, control measures should also
emphasize: 1) the protection of feed and water sources from contamination by
dogs, foxes, and coyotes; 2) prompt disposal of dead fetuses, dead calves, and
placenta; and 3) steps to eradicate dogs or wild canines from the premises or
prevent their contact with the female herd during calving. One interesting observation that has been
reported is that beef herds with cattle dogs were less at risk of finding neosporosis. It is postulated that the farm dogs played a
role in keeping coyotes and foxes away from the cow herd. In contrast, several studies with dairy herds
link higher numbers of dogs on the farm with a higher risk of neosporosis.
Conclusion
Because differences exist between reproductive diseases
based on transmission, duration of shedding, persistence in the environment,
and other factors, it is difficult to design a one-size-fits-all-diseases
biosecurity program. However, the
following guidelines should be considered as a base from which the producer and
veterinarian can design an effective biosecurity plan. The following guidelines are based on
incoming breeding stock, but it is important to remember that all incoming
animals should be subjected to an isolation/biosecurity plan also.
1. Isolation facilities should:
- be sited at least as far away from the existing
herd so as to not allow nose-to-nose contact between new and existing
groups.
- not have manure runoff or drainage to or from the
existing herd.
- be planned so that equipment and personnel do not
have to be shared between sites.
Alternatively, cleaning and disinfection, changes of clothes and boots
should be employed, and chores done on the isolation animals after the
existing herd.
2. Hold animals in isolation for 30-60 days.
3. Treat incoming females with a long-acting
tetracycline to assist in clearing the carrier sate of L. hardjo-bovis.
4. Test incoming animals for BVD PI with an
ear-notch test. Promptly remove positive
animals.
5. Perform other diagnostic tests as outlined by
the herd veterinarian early on during the isolation period.
6. Employ appropriate vaccines (generally MLV
4-way virals plus Vibrio-Lepto (including L.
hardjo-bovis), depending on the age and reproductive stage of incoming
animals.
Because most infectious disease, including reproductive disease,
enters the herd via incoming animals, a proper biosecurity plan for these new arrivals
is the best defense against potentially devastating diseases and reproductive
loss.
References
Barr BD, Anderson ML. Infectious diseases causing bovine abortion
and fetal loss. Vet Clinics
Givens MD. A clinical, evidence-based approach to
infectious causes of infertility in beef cattle. Theriogenology 2006;66:648-654.
Sanderson MW, Gnad DP. Biosecurity for reproductive diseases. Vet
Clinics
Whittier D. Lepto: a new vaccine, a new disease? Livestock
Update,
Wikse S. Management of infectious reproductive
diseases in beef cattle herds. Proceedings, Applied Reproductive Strategies
in Beef Cattle,