J.W. Fisher,
telephone:(613)258‑8336
ext. 447
e‑mail:jfisher@kemptvillec.uoguelph.ca
P.I.
Menzies,
telephone:(519)824‑4120
ext. 54043
e‑mail:pmenzies@ovc.uoguelph.ca
Summary:
Maedi Visna (MV) has been identified as a common viral infection
in
Two benefits were
identified from being MV free, better breeding sales and some improvement in
ewe productivity. The benefits to
breeding sales warranted eradication within sheep flocks. With a mere 10% improvement in sales on 25%
of lambs sold for breeding stock a producer would expect to breakeven just
shortly after becoming ‘A’ Status. This
outcome was robust for all combinations of flock size, ewe and breeding sales
values, and bleeding costs.
Commercial sheep
producers did not find the same positive outcome. With low prevalence of the disease, few
benefits accrued. Only with prevalence
over 10% with low bleeding costs and large flocks would commercial producers
show a reasonable payback period of about 6 years, and then only with the
Monitored Program. Payback would never
be reached on the Whole Flock Program for commercial sheep producers.
Key
Words: Maedi Visna;
Economics; Sheep; Flock Certification Program; Disease
Introduction:
Maedi Visna (MV) is a common viral infection in
The purpose of
removing all MV positive individuals from the flock is to eradicate this
disease in
Productivity
losses due to MV are especially important to commercial sheep producers, who
rely on the weight, quantity and quality of their animals to turn a
profit. For sheep breeders, more
important is the simple ability to state that their sheep are MV ‘free’. Being MV free may result in an improvement of
breeding sales, particularly if their customers understand the importance of a
good health management process.
In addition to
these expenses, there are also various expenditures associated with enrolling
in the program. These include ear tags,
isolation facilities, veterinary supplies, laboratory charges, paid labour and
various equipment fees, among others.
This project will attempt to quantify the costs associated with a MV
eradication and certification program.
The main objective of this project is to quantify the costs
associated with a Maedi Visna Flock Certification Program (MVFCP). In addition, an attempt will be made to
determine the conditions under which this program will provide net economic
benefits for different sectors of the sheep industry.
Review of the Literature:
Although considerable work has been done with respect to Maedi
Visna control programs, there is very little research concerning their economic
consequences. The costs and benefits of
a disease eradication program have a direct influence on whether the program
will be implemented and followed by producers.
However, there is seldom a report concerning Maedi Visna that does not
acknowledge the fact that it has important financial implications (Houwers et
al, 1984; Sihvonen et al, 2000; Varea et al, 2001).
Fortunately,
there is a growing field of research, animal health economics that evaluates
the economic losses due to disease and the expenses that accompany an
eradication program. Research in this
area is not only concerned with specific medical conditions in livestock, but
also concentrates on developing general guidelines for evaluating the costs of
disease and disease control. This is
particularly useful since the costs of disease vary with the type of disease
and the type of control program used (Putt et al, 1988).
Davies (1980)
recognizes four significant elements that contribute to the costs of a disease
eradication program. The first variable
that must be taken into consideration is the amount of disease present in the
flock. It is reasonable to state that as
the prevalence of disease in the flock increases, the costs associated with
eliminating the disease will also increase.
Secondly, the value of the stock is determined by the value of the
animal with the MV virus, the cost of culling the animal, and the loss of farm
income due to time spent on eradication procedures. A third important factor is the effect of the
disease on trade, which is of particular importance to sheep breeders. Finally, the cost of serological testing
procedures can be measured via the cost of collecting blood samples, the cost
of laboratory testing, and the time scale of the eradication program.
This last
variable is often neglected in the literature, but it is of great
importance. Although a minimum of four
years is required for a flock to become MV free, more time is needed to ensure
complete disease eradication (Houwers et al, 1984). The additional costs of maintaining the
program, even after an apparent elimination of the disease from the flock, must
be taken into consideration.
Putt et al (1988)
distinguish between non‑medicinal prevention and medicinal measures when
proposing a method to evaluate the costs of a disease control program. Non‑medicinal prevention includes
factors such as the producer’s time spent with the flock for disease control
purposes or the construction of new buildings, specifically assembled for the
disease eradication program. In comparison,
medicinal measures include the identification of the disease through diagnosis
and surveys followed by the treatment of the disease. Costs of treatment are a function of the
reported incidence and severity of the disease (Wesley, 1987). For the MV virus, the only current treatment
is to cull all infected sheep (Houwers et al, 1984) and to remove lambs born to
infected ewes immediately upon birth (Bruère & West, 1993). Therefore, culling of all affected sheep can
also be classified as the treatment of the disease. Preventive measures such as culling are
generally seen as quite costly, but necessary (Horst, 1998; Lassauzet et al,
1991; Wesley, 1987).
Overall, there is
a great deal of repetition in the literature regarding those variables that
contribute to the costs of a disease eradication program. As the current veterinary services to
individual farms are changing from the traditional ‘first‑aid’ practices
to planned prevention and control programs, the role of the veterinarian is
becoming increasingly important (Dijkhuizen et al, 1991). As such, veterinary fees must be accounted
for when estimating the costs of a disease eradication program. Labour performed by the farm operator and
other staff, including those involved in administrative duties, must be
accounted for when considering the costs associated with a disease control
program (Berger, 1980; Caporale et al, 1980; deGraaf et al, 1999; Putt et al,
1988; Renkema, 1980). In addition,
various medical equipment, such as syringes, needles and/or vials contribute to
the costs of the control program (Caporale et al, 1980; Paniagua Arellano &
Diaz Yubero, 1980; Putt et all, 1988).
Lee (1981) refers
to certain indirect costs, such as training and education of farmers. Although these expenses were not included in
the economic evaluation of the disease in Lee’s research (due to a lack of
information), their importance was noted.
Having a solid understanding of the disease that is being dealt with is
essential for a farmer, and costs due to education are often incurred.
Of course, there
are several benefits that accompany a disease eradication program. With a control program in place, there will
be increases in the production of meat, milk and wool, a rise in birth rates
and an improvement in breeding sales (Oluokun, 1980; Paniagua Arellano &
Diaz Yubero, 1980). Any constraints that
the disease imposed on the flock, such as limited productivity, will be lifted
once the disease is eradicated. Benefits
such as these are generally referred to as ‘indirect benefits’ (Putt et al,
1988).
As is the case with almost any disease, the
profitability of a sheep flock is limited by the presence of Maedi Visna. Infected ewes are only two thirds as likely
to lamb as uninfected ewes, and infected ewes have 0.13 fewer lambs born per
ewe exposed to the ram. Thus, the first
main effect of the Maedi Visna virus (MVv) is that it causes a reproductive
loss to the sheep producer (. In contrast, Dohoo et al
(1987) found that although MV significantly decreases conception rates, it has
no effect on lambing rates.
Second, since lambs born to infected ewes
weigh 0.16 kg less at birth than lambs born to uninfected ewes, there is a
serious effect of the disease on the birth weight of lambs (. Similar results were
found by Keen et al (1997), who reported that lambs reared by MV positive ewes
weighed 0.15 kg less at birth.
A third major
effect of MV is its influence on lamb growth.
Keen et al (1997) report that a single lamb nursing an infected ewe will
weigh 0.59 kg less at 56 day weaning than a lamb nursing an uninfected
ewe. Menzies (internet resource) reports
that twin lambs nursing infected ewes will each weigh 1.03 kg less at 60 days
than twin lambs nursing an uninfected ewe.
Finally, infected ewes will wean 11.0 pounds less lamb per ewe exposed
to the ram. This loss of profitability
contributes to the cost of the disease.
Once a disease eradication program is put into effect, the constraints
of the disease will be lifted, and there will be many visible benefits.
The literature
seems to be somewhat divisive on the amount of economic losses due to this
disease. Identification of a mere 11
pounds of lamb per year lost to a sero‑positive ewe certainly is not
enough to warrant eradication programs.
Vilmos (1996) concluded based on histopathological changes in 50% of
culled ewes in his study, that Maedi Visna is one of the most frequent causes
of diminished life production and thus it causes significant economic losses.
There is a great
deal of literature dedicated to helping individuals in making decisions
regarding livestock management, particularly under conditions where disease is
present. The decision process usually
pertains to evaluating various disease control policies and incorporates their
economic aspects.
Dijkhuizen at al
(1991) and Renkema (1980) refer to positive and normative approaches when
dealing with the costs of a disease control program. A positive approach will evaluate the field
data directly, using statistical/epidemiological models. In contrast, the normative approach makes
predictions based on existing knowledge.
Results are generated by the method of system modeling, enabling a
simulation of the effects of various management decisions and control strategies. The data used in the normative approach may
be derived from field data. Since the
field experiments used in the positive approach are costly and often interfere
with the implemented program, a normative procedure may be the best route to
take. Bennett (1992b) highlights the
benefits of using such a simulation approach; it is not necessary to experiment
with the system itself, but only a model of the system. The aim of the simulation is to see ‘what
happens’ under a number of different circumstances or assumptions.
Bennett (1992b) refers
to a 1988 study by
Bennett (1992a)
describes the construction and possible uses of a simple decision support
system. In order to assess the economic
effects of a disease and its eradication program adequately, a model should be
constructed that allows one to produce ‘best’ and ‘worst’ case scenarios, or
any other scenario required by the analyst.
The purpose of this model is not only to estimate the costs and benefits
of the disease eradication program, but also to predict what will occur when
estimates and values of different parameters are altered and to investigate
various ‘what if’ questions. It is particularly
useful if this model can be modified to specific farm situations, for example,
the size of flock or value of livestock.
It should be possible for the data to be entered into the model with
relative ease, and the changes due to any adjustments should be seen
immediately.
In Bennett’s
(1992a) model, three different options for disease control are evaluated: ‘Do
nothing’, "Vaccinate’, and ‘Test and cull’ (the model pertains to the
Bovine Pestivirus Syndrome, or BPS). By
comparing the costs of different control strategies, it is easy for the farmer
to make wise decisions concerning the health of the flock.
Putt et al (1988)
further break down types of models into dynamic versus static and deterministic
versus stochastic. While static models
often deal with the average of a set of values once a system has reached
equilibrium, dynamic models take into account daily values over a certain
period of time. In contrast, a
deterministic model describes the situation which would arise if all the
variables had average values, while a stochastic model allows the variables to
take values from a range of values according to some probability
distribution. In the case of Maedi
Visna, a static model may be the best way to measure the costs of an
eradication program, since it is assumed that flock size does not fluctuate
over time for each scenario.
In addition,
there are some extremely basic models discussed in the literature. In research by Oluokun (1980), a flow chart
illustrates a simple economic evaluation of a disease control program. The total cost of a disease eradication
program, such as the Maedi Visna flock certification program, will equal the
costs of controlling the disease in addition to the benefits from eliminating
the disease.
There are considerable
costs associated with disease control programs, but these costs are necessary
in order to reap the benefits of having a disease free flock. It is generally found that although most
disease eradication programs are quite costly, especially in their early years,
the benefits outweigh the costs by the time that the program is completed
(Davies, 1980; Polydorou, 1982; Putt et al, 1988). This is particularly true concerning the
Maedi Visna flock certification program, in which culling of sero‑positive
sheep is the only way to eliminate the disease.
McInerney (1996)
defined the responsibility of economists in the question of disease control as
those who will help set the boundary to controls. Some systemic diseases (for example mastitis)
may optimally exist at some level if we consider the balance between control
costs and controllable losses due to the disease. Where a disease is not systemic and can be
controlled only by eradication, such as with Maedi Visna, then the optimal
level will exist (if the losses are great enough) or it will not exist at all
for that particular economic environment.
Taken directly
from McInerney, figure 1 shows a hypothetical efficiency frontier for a
disease, below which is impossible to achieve.
The y‑axis represents production losses due to the disease which
includes loss of productivity, death loss, loss of markets, etc.. The x‑axis represents expenses to
control and fight the disease, such as veterinary services, medicines, Flock
Health Level I expenses, etc. When eradication is necessary, the efficiency
frontier L’L" will intersect the x‑axis. Maedi Visna is such a disease. Isocost lines must be by definition a 45°
angle to the x‑axis and represent combinations of equal cost to the
disease if we accept the basic premise that the cost of the disease is equal to
the losses plus the control expenditures.
McInerney argues that the optimal disease level is seldom at zero. The isocost line that is tangent to the
efficiency frontier defines the optimal level of disease loss and control
expenditure, at M.
With Maedi Visna
at the farm level, there is no middle ground.
Either the producer eradicates the disease with all the requirements of
the program or simply tries to minimize the chances of having lots of the disease
by careful purchasing of replacement animals and culling of suspect
animals. In this study we will attempt
to demonstrate this concept given commercial and breeding enterprises.
Materials
and Methods:
The original protocol
for this study involved each participant returning annual business reports for
analysis. Due to the low numbers
enrolled in the program, a static normative model of the MVFCP was
designed. Phone interviews were
conducted in order to collect data and this information was entered into the
model. The model reported the costs of
participation in the project. Written
feedback was given to the participants shortly after the phone interview took
place. Each participant was sent a
schematic of the MVFCP, copies of the Whole Flock and Monitored flock programs
pertaining to their individual situation, and a letter explaining the two
programs. Participants were invited to
contact the researcher if they had any questions or comments. This served as a beta test for the model.
Because the average results of the
16 participants in the program were not of particular significance to anyone,
they were merely summarized. Of more
importance is the effect of certain flock characteristics on the economics of
the program. A flock size of 100 and
500 breeding ewes was stated and then scenarios were proposed. The scenarios had different variables, such
as the type of sales (commercial or breeding stock), type of program (Whole
Flock versus monitored), observed increase in breeding sales and value of
sales, value of ewes, bleeding costs, labour costs, prevalence of the disease,
and the occurrence of positive tests later in the process. The dependant variables observed included
cost to reach ‘A’ Status and how long it would take to breakeven.
Results
and Discussion:
The computer model was programmed in Lotus 123 Release 5. The models are fairly straight‑forward,
accounting for cycles involved in the program protocols (see Appendix I for a
copy of the models). The simplicity of
the models can be largely attributed to the assumption that producers were at a
Level I health status1 prior to enrolling on the Maedi
Visna Flock Certification Pilot Project (MVFCP). By doing this we have removed many
complicating issues for comparing productivity gains due to this program. Indeed, part of the research protocol was
that participants must be on the Ontario Sheep Health Program which ensures
they were at Level I health status. Therefore,
just the costs of Maedi Visna testing and the benefits from this testing need
be modeled.
Fifteen producers
enrolled in the MVFCP were telephone surveyed using the model. Twelve producers were breeding flocks
enrolled in the Whole Flock Program, one breeder was on the Monitored Program,
and two commercial producers were on the Whole Flock Program. Table 1 displays the average of all farms on
the Whole Flock program (other summaries are not shown due to the small data
set). All of these producers sold
breeding stock.
On average,
producers enrolled on the Whole Flock Program had 149 ewes. Some expenses were invested in isolation
facilities, although these were not elaborate.
Double ear tags were required, so one additional tag per animal was
accounted for. Participants were
required to register in the OSHP, which costs $75, and most partook in some
sort of education program concerning flock health or Maedi Visna
specifically.
Bleeding charges
included laboratory fees, veterinary services and labour. Laboratory fees range from zero for the
general population, $2.50 per test if enrolled in the MVFHP, to $8.50 which is
the cost recovery rate proposed by the Canadian Food Inspection Agency. Veterinary services range at about $3.33 per
sheep, which is a flow rate of about 30 sheep per hour. Enough help is needed to assure this flow
rate. Operator labour was charged at
$1.05, hired labour at $0.17 and labour to keep necessary records at $0.75 per
test. Table 1 shows veterinary services
and labour at less than these rates because some bleeding was done by the
research team at no charge. Isolation
labour was $13.33 per ewe put in isolation.
The value of
breeding ewes was $374 and these were depreciated over 6.75 years. The average cull value was $69. The average age at culling was 3.8 years. Positive tests where ewes were culled cost
the producer the remaining depreciation between 3.8 and 6.75 years (straight
line depreciation).
Benefits from
Maedi Visna eradication can be two fold, a productivity increase or an
improvement in breeding sales from displaying a Maedi Visna free status. The literature states a commercial benefit of
11 pounds of lamb per infected ewe. (In the author’s opinion, this may
underestimate the impact of Maedi Visna on the productivity of a flock). Breeders who advertise various flock health
credentials, find it easier to sell stock to shepherds. Those surveyed sold 26% of their stock as
breeding stock and estimated an improvement of 11% in breeding sales. This improvement in breeding sales could be
price or quantity.
The results of
this group of producers, with an average of 7.25 positives on the first test
and 5.83 culls were costs of $5,207 to become ‘A’ Status, on average. By this time benefits of $14,851 had accrued. This group would break even 1.5 years before
becoming ‘A’ Status. Also this group
would have taken five years to become ‘A’ Status. The majority of the benefits come from
improvement in breeding sales. In fact
only a 3.7% improvement in breeding sales (on 26% of lambs being sold for
breeding stock) is needed to breakeven by the time ‘A’ Status is achieved.
The variables of
importance to the economic success of the MVFCP program appear to be flock size
(because the random sample size becomes relatively smaller as flock size
increases, see appendix II), bleeding costs, ewe value and breeding sales
value. To summarize the effects of these
variables on the costs/benefit of the MVFCP, scenarios are presented for four
groups of producers; breeder and commercial producers in either the Whole Flock
Program or the Monitored Program. The
standard scenario includes isolation facilities at $125, ear tags at $0.36,
OSHP at $75, education at $150, salvage at $69, isolation labour at $13.33 per
animal, age at 3.8 years, 6.75 years of use for ewes, 11 pounds in added
productivity, 10% improvement in breeding sales, 2 lambs per ewe per year, 25%
of sales as breeding, and commercial sales at $100.
Bleeding costs
were varied between $4.50 and $15.00 per test while ewe value was varied
between $200 and $600 per ewe. Direct
bleeding costs consisted of six items, lab charges, vet supplies, and labour
for record keeping, help, operator and veterinarian. It doesn’t matter how the cost of each of
these are distributed. Also, to reflect
the value of ewes as this affects the value of her lambs, the value of breeding
sales were set to be the same as the ewe value, so these two variables act
together. Breakeven (years) shows how
long it will take for the producer to cover the direct expenditures with reduced
loses (the x and y‑axis in figure 1) (see footnote 1).
Breeding flocks
with 100 ewes and 500 ewes on the Whole Flock Program are evaluated in Table
2. All scenarios had very early payback
periods of either just before becoming ‘A’ Status or just shortly after. With 500flock size, there is a slight
improvement in all payback periods, however small. This has implications for sheep breeders in
Breeding flocks
enrolled in the Monitored Program (Table 3) again show very encouraging payback
periods. Certainly the Monitored Program
is cheaper because it uses random samples, however it takes one additional
test. The status is not as good, and
with smaller flocks, the random sample number is relatively large compared to
the flock size. So cost savings between
the Whole Flock and the Monitored Programs are minimal, particularly in smaller
flocks.
Commercial flocks
in contrast, never have the opportunity to breakeven given the standard
scenario presented. The annual cost of
testing is always greater than disease losses with the Whole Flock Program
(Table 4). This is because without the
prevalence of the disease in a flock, there is no benefit seen after
testing. It appears that those who
should test are those who suspect they have high prevalence of Maedi Visna in
their flocks.
Commercial flocks
of any size had no chance of payback in the Monitored Program given the
representative data (Table 4). However,
commercial operations would breakeven when prevalence is greater than 3.6
percent with large flocks (500 ewes) and low bleeding costs, in 308 years. At a 10% prevalence the payback is in 5.9
years after becoming ‘B’ Status.
The implications for the
Efficiency
frontiers for Maedi Visna control on
1. Breeding
operations on the Whole Flock program show potential losses of $13,500 and
expenditures of $1,930 to become ‘A’ Status (100 ewes with value on ewes/sales
at $600), figure 2. This has an average
slope of ‑7 which is less than an isocost’s slope of ‑1 (45°
angle). As long as the curve of the
efficiency frontier L’L" touches the isocost Cm at the x‑axis
intercept, then the point of the x‑axis intercept is the optimal control
point for this farm. And as such this
demonstrates that eradication is the most economical option in this case, point
m in figure 2.
2. However, a
commercial operator with 500 ewes, low bleeding costs and 10% prevalence would
save production losses of $1,100 and incur control expenditures costs of $3,209
to achieve a ‘ B’ Status, figure 3. This
is the scenario where breakeven will occur in another 5.9 years after becoming
a ‘B’ Status (taking four years). Over the next 5.9 years the efficiency
frontier #1 for this producer is shifting to the northeast until it’s slope,
frontiers #2 and #3 become equal to ‑1.
The frontier shifts because the annual costs of testing is less than the
annual benefits after the first year or so when all sero‑postitive
animals are disposed of. Eventually the
frontier will be above an isocost where again, the optimal point will be at the
x‑axis intercept (as is the case in figure 2).
3. Also for a
commercial operator (figure 4) on the Whole Flock Program (100 ewes, low
bleeding costs and 10% prevalence) the savings from production losses would be
$275 and control expenditures would be $2,824 with no potential to
breakeven. This is because the annual
costs exceed the annual returns as time goes on. The efficiency frontier J’J" has a
slope that is more than ‑0.1 and will never shift lower than a slope of ‑1. Therefore the isocost Cx will
intersect the efficiency frontier J’J" at an optimal point Y, that does
not represent eradication. Actually,
point Y is very close to the y‑axis intercept, suggesting that very
little control expenditure is economically warranted in Maedi Visna control,
for this scenario. The implication is
that commercial producers with low prevalence should practice selective culling
and good bio‑security and not enroll in the MVFCP.
This analysis varies slightly from
that of McInerney and that of Chi, in that the costs of this disease
(production losses plus control expenditures) will not have a particular time
frame. A minimum of four years is needed
to gain ‘A’ Status, three years for a Monitored ‘B’ Status and breakeven can
happen over any number of years thereafter.
And so the efficiency frontiers presented are quite mobile in time. Their tendency to shift around should not
effect their use to explain the concept of optimal disease control.
Maedi Visna testing involves a few
other issues that may not have been accounted for as yet in this analysis. Depending on the organization of the farm,
pre‑bleeding assembly of animals may be easy or arduous. Meticulous record keeping needs to be done
and strict bio‑security measures followed. Much effort, time and organization goes with
the program. And then the outside risk
that once ‘A’ Status has been achieved, at some point in the future, there may
turn up a positive test. The dollar cost
of this one positive test would be that a whole flock test would need to be
done the next time and you would cull the culprit. However, because you would loose your ‘A’
Status, you would need to remove this designation from your promotion, which
may cost you breeding sales. The
implication of this one positive test could be relatively large.
Conclusions:
The Maedi Visna Flock Certification Pilot Program assumes that
producers will enroll in the Ontario Sheep Health Program, educate themselves
about controlling disease, test their sheep on a regular basis, cull all sero‑positive
animals, and practice at Level I flock health management, including bio‑security
measures. Without this type of protocol,
the eradication program will not work.
Also, eradication seems to be the only measure to control the disease. And the two benefits of this program have
been identified as a savings of 11 pounds of lamb per year per infected ewe,
and for breeders a more significant bonus of improved sales if displaying a
certified status.
Within these
parameters, there seems to be a good economic return for breeders in
Commercial
producers on the other hand have a conundrum.
If they don’t have the disease, they will have no benefit to being on
the program. At levels above 10% prevalence,
with low bleeding costs, commercial producers on the Monitored Program begin to
show a reasonable payback of about 6 years.
Some protocols need to be adjusted to encourage more participation from
commercial producers.
More research is needed in the
assessment of production losses due to this disease. The commercial loss of 11 pounds per ewe per
year is not enough to warrant eradication or alarm around this disease. In many countries Maedi Visna is a reportable
disease, some national eradication programs have occurred over the years, all
which suggests that this disease is more destructive than stated in the
literature.
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