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From: Terry S. Singeltary Sr. (wt-d6-180.wt.net)
Subject: A Quantitative Assessment of the Possible Role of Nonambulatory Cattle in Transmissible Spongiform Encephalopathy in the United States
Date: October 21, 2004 at 4:02 pm PST

-------- Original Message --------
Subject: A Quantitative Assessment of the Possible Role of Nonambulatory Cattle in Transmissible Spongiform Encephalopathy in the United States
Date: Thu, 21 Oct 2004 17:05:21 -0500
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy
To: BSE-L@UNI-KARLSRUHE.DE


##################### Bovine Spongiform Encephalopathy #####################

A Quantitative Assessment of the Possible Role of Nonambulatory Cattle in
Transmissible Spongiform Encephalopathy in the United States

Background

The emergence of bovine spongiform encephalopathy (BSE) in Great Britain and other countries has
focused attention on certain cattle populations in the U.S. One such population is nonambulatory
cows. The term nonambulatorY cow (or "downer" cow) refers to any cow that is recumbent when
the reason for the recumbency is unknown (1,2). Some researchers feel that nonambulatory cows
occur secondarily to low blood levels of calcium (2,3), while others suggest that nonambulatory
cows occur as a sequela to prolonged recumbency due to a variety of other causes (e.g., mastitis,
metritis, calving paralysis, and milk fever) (4). Though many causes for nonambulatory cows have
been proposed, most studies have failed to find evidence of any of these conditions in a large
fraction of the nonambulatory cows. Nonambulatory cows are alert and unresponsive to therapy if
treated. Terminal cows due to a known disease are not considered nonambulatory. For the
purpose of this report, the term nonambulatory cow refers to a cow that is culled because it is
unable to stand.

BSE is a neurologic disorder that affects cattle. BSE has occurred in seven countries, and is
believed to have been initiated through the feeding of meat and bone meal contaminated with
sheep scrapie. BSE is not known to exist in the U.S., but it has been suggested that an
unidentified transmissible spongiform encephalopathy (TSE) may be present in U:S. nonambulatory
cows (5). This hypothesis is based on an alleged association between feeding nonambulatory
cattle to mink and outbreaks of transmissible mink encephalopathy (TME) (6,7). There have been
five reported outbreaks of TME in the United States; one in 1947, three in the early 1960's, and
one in 1985. The outbreaks in the early 1960's were associated with common food sources and-
movements between farms (8). The large fraction of nonambulatory cases that are due to - -
unknown cause provides a basis for the hypothesis that a TSE may exist in U.S. cows and be a
source of TME. The purpose of this report is to describe the occurrence and disposition of
nonambulatory cows in States with both dairy and mink industries, and to assess the potential role of these cattle in the transmission of a spongiform encephalopathy.

Nonambulalory Cow Prevalence and Disposition

The prevalence of
nonambulatory cattle in the
U.S. is difficult to estimate due
to the numerous options for
disposition of such animals.
Nonambulatory cows may go to
Federal or State slaughter
plants, to rendering plants, be
custom slaughtered, sold
locally, or killed and disposed on
the premises (Figure 1). Of
particular interest are the
number sold locally to mink
producers. The greatest
number of nonambulatory cows
are believed to go to rendering.
Rendering facilities do not
maintain records on numbers
and causes of nonambuiatory
cows as nonambulatory cows
represent only a small fraction
of incoming rendered product,

Nonambulalory Cow* Disposition

Figure 1 (not applicable...TSS

and acquisitions are made by drivers who are not trained nor charged with responsibility to assess reasons for moribundity.

Three sources of information on the prevalence and disposition of nonambulaiory cows were
utilized for this report: a review of the literature; State-inspected slaughter plants that slaughter nonambulatory cattle exclusively; and a survey to determine incidence and disposition patterns at the farm level.

Literature Review

The reported incidence of nonambulatory cows varies with the definition used. The annual
incidence of nonambulatory cows was 21.4 per 1,000 cow-years at risk, in dairy herds
participating in the Dairy Herd Improvement Association in Minnesota in 1983. Cows unable to
stand for no obvious reason, including those that eventually recovered, were considered to be
nonambulatory (1). A prospective study of 34 dairy herds in New York revealed that 28
nonambulatory cow cases occurred out of 7,763 lactations (4,092 animals) during a 4-year period,
or 3.6 per 1,000 cow-years at risk (9). For that study, cows that recovered were not reported as
nonambulatory.

Concerning disposition of nonambulatory cattle, Milian-Suazo et at. (10) reported that more than
one-half of nonambulatory cows were culled in the same lactation, it has also been reported that
some mink ranchers have contracts with local slaughter plants to pick up nonambulatory or dead
cows (8). The entire carcass is reportedly ground into feed at the mink facility.

Antemortem Slaughter Inspection in Federal and State Plants

One possible endpoint for nonambulatory cows is a Federal or State slaughter plant. The United
States Department of Agriculture: Food Safety Inspection Service (USDA:FSIS) maintains a record
of animals condemned antemortem due to a variety of reasons, but there is no category specifically
for nonambulatory cows. State-inspected slaughter plants may also accept nonambulatory cows.
The only available data on nonambulatory cows from State plants came from Wisconsin, which has
the largest number of milk cows in the U.S. and has four State-inspected plants specifically for
nonambulatory cows. In 1992, these four plants slaughtered a total of about 10,000
nonambulatory cows (G. Jacobsen, AVIC, USDA:APHIS:VS, personal communication). Neither the
number of cows that were condemned antemortem and not slaughtered nor the slaughtered cows'
State of origin was known.

Farm-level Information on Numbers and Disposition Patterns

Because data from slaughter were limited and do not capture the fraction of nonambulatory cows
going directly from farm to mink producer, a survey was conducted to determine the incidence and
disposition of nonambulatory cows at the farm level. Sampling was from States with both dairy
and mink industries, and was not random. Seven States were selected based on geographic
distribution and ranking by numbers of milk cows and mink bred. Twenty-one dairy practitioners
were selected from lists provided by university faculty, dairy organizations, and USDA contacts.
Each practitioner was asked to select three herds to sample for the study, one from each of three
size categories (small n<-.50; medium 51 100) . The number of practitioners
selected for each State was calculated based on the number of dairy cows per State. Eight
practitioners were contacted in Wisconsin; four in New York; three in Pennsylvania; three in
Minnesota; and one each in Idaho, Utah, and Washington. Eighty-one percent (17/21) of the
practitioners responded. The response rate by State was 100 percent for New York, Pennsylvania
Wisconsin, and Idaho; 33 percent for Minnesota; and 0 percent for Washington and Utah. A total
of 51 herds was represented.

Page 22

Incidence of Nonambuiatory Cows in the Study Sample

Responding veterinarians reported 363 nonambulatory cows out of 13,429 cows on the 51
premises for 1990-1992, for an incidence of 27 per 1,000 cow-years at risk. Incidence of
nonambulatory cows was 35, 21, and 28 per 1,000 cow-years at risk for small, medium, and large
herds, respectively. There was no evidence of regional differences in rates of nonambulatory cows.

Only those cattle without identifiable reasons for being nonambulatory have been hypothesized as
potentially having a TSE. The incidence of nonambulatory cows of unknown cause reported in the
study sample for 1992 was 8 per 1,000 cow-years at risk. Nonambulatory cows of unknown
cause accounted for 22.8 percent of all nonambulatory cows. Incidence for nonambulatory cows
of unknown cause in 1992 was 12, 5, and 8 per 1,000 cow-years at risk for small, medium, and
large herds, respectively.

Disposition of Nonambulatory Cows in 1992

For 1992, there were 158
nonambulatory cows reported in
the study sample. The initial
disposition of more than half of the
nonambulatory cows was
rendering (Table 1). Most of the
remaining nonambulatory cows
initially went to slaughter, with
those condemned at slaughter
potentially going to rendering or to
mink producers. Of the 6.3
percent of nonambulatory cows
that went directly to mink
producers, half had no identifiable
reason for being nonambulatory.


Table-1 Initial Disposition of Nonambulatory Cows from 51 Dairies in 1992

Disposition Number Percent*

Renderer 83 52.5

Regular Slaughter 45 28.5

Mink Producers 10 6.3

Dealer 10 6.3

Custom Slaughter 9 5.7

Livestock Market 1 0.6

Total 158 100.0

* Total* may not add due to rounding

There was no correlation between
distance to disposition site and
method of disposition. The
average distance from a herd to:

the nearest slaughter plant was 29
miles; the nearest renderer was 25 miles;
and the nearest mink ranch was 36 miles.

Nonambulatory Cattle as a Potential Source of TSE

In this study, Wisconsin was the only State in which mink producers were reported to receive
nonambulatory cows directly from dairies. However, given the small number of surveyed herds this
finding is likely a result of the sampling design. Because mink producers pay a premium for
nonambulatory cows, it appears reasonable that the practice of feeding nonambulatory cows to
mink could occur wherever both large numbers of dairy cows and mink are found. As many as
2,157(3) nonambulatory cows per million milk cows, or a total of 9,482 nonambulatory cows, could
have been fed to mink in the 7 surveyed States in 1992. Based on the sample response, only half
of those cows would have had an identifiable reason for being nonambulatory. This equates to an
estimated 4,741 nonambulatory cows that were, hypotheticaily, a potential source of TSE in the
surveyed States.

(3)This estimate does not account for any nonambulatory cows received from slaughter plants.

Page 23

The five reported outbreaks of TME in the U.S. reveal no discernable trend. Assuming an average
of 2,000 mink farms in the U.S. during the last 50 years, one outbreak of TME has occurred per
20,000 mink farm-years. Extrapolating from the data gathered in this study, 66,374
nonambulatory cows have been fed to mink in the 7 surveyed States since the last reported
outbreak of TME in 1985. Of those, 33,187 would have had no identifiable reason for being
nonambulatory and were hypothetically a potential source of TSE. Given the severity of signs and
number of mink affected by TME it is unlikely that outbreaks have gone unreported. If any form of a TSE (infectious, spontaneous, or other) occurs in U.S. cattle that is transmissible to mink in the form of TME, then it must be exceedingly rare or the conditions for its transmission must be highly specific and unusual. Nonetheless, studies are underway at the State and Federal levels to further characterize the disposition of nonambulatory cows and usage on mink farms.

Summary

Little attention has been given to nonambulatory cows in the past. The emergence of BSE and
TME has brought the issue of nonambulatory cows into focus. Limited information is available on
the numbers and disposition of nonambulatory cattle in the U.S. Available estimates vary greatly, depending on how the condition is defined. Federal and State slaughter plants provide information on antemortem condemnation rates due to a variety of reasons, but no data exist that capture all nonambulatory cows.

Data from a nonrandom survey of dairy herds in States with mink were used to estimate the
incidence of nonambulatory cows between 1990 and 1992. In surveyed herds, the incidence of
nonambulatory cows was 27 per 1,000 cow-years at risk. In 1992, the incidence of cows which
were nonambulatory for no obvious reason was 8 per 1,000 cow-years at risk. Over half of the
nonambulatory cows reported went to rendering. Most of the remaining nonambulatory cows
initially went to slaughter and 6.3 percent went directly to mink.

An estimated 4,741 nonambulatory cows hypothetically considered to be potential sources of TSE
may have been fed to mink in the 7 surveyed States in 1992. This equates to 33,187 such cows
fed to mink since the last reported outbreak of TME in mink. Given this large number of
nonambulatory cows fed to mink, the historic and current mink population, and the infrequent
occurrence of TME, if TSE exists in cattle in the U.S. it must be very rare or transmissible to mink only under very unusual conditions.

References

(1) Cox, V.S., Marsh, W.E., Steuernagel, G.R. et al. 1986. Downer cow occurrence in Minnesota
dairy herds. Prev Vet Med 4:249-260.

(2) Fenwick, D.C. 1969. The downer cow syndrome. Aust Vet J 45:184-188.

(3) Curtis, R.A., Cote, J.F., and Willougnby, R.A. 1970. The downer cow syndrome. A
complication, not a disease. Mod Vet Prac 51:25-28.

(4) Cox, V.S. and Onapito, J.S. 1986. An update on the downer cow syndrome. Bovine Prac
21:195-199.

(5) Marsh, R.F. 1992. Transmissible mink encephalopathy, scrapie and downer cow disease:

potential links. Proceedings of the Third International Workshop on Bovine Spongiform
Encephalopathy, Bethesda, MD, pg. 1-7.

Page 24

(6) Marsh, R.F. 1990. Bovine spongiform encephalopathy in the United States. J Am Vet Med
Assoc 196(10):1677.

(7) Burger, D. and Hartsough, G.R. 1965. Transmissible encephalopathy of mink. In: Gajdusek,
D.C., Gibbs, C.J., and Alpers, M. (eds.) Slow, latent, and temperate virus infections. U.S.
Department of Health, Education and Welfare, National Institute of Neurological Diseases
and Blindness, Monograph No. 2, pg. 297-305.

(8) Bridges, V., Bleem A., and Walker, K. 1991. Risk of transmissible mink encephalopathy in
the U.S. Animal Health Insight, Fall, 1991 pg. 7-14.

(9) Milian-Suazo, F., Erb, H.N., and Smith, R.D. 1989. Risk factors for reason-specific culling of
dairy cows. Prev Vet Med 7:19-29.

(10) Milian-Suazo, F., Erb, H.N., and Smith, R.D. 1988. Descriptive epidemiology of culling in dairy
cows form 34 herds in New York state. Prev Vet Med 6:243-251.tss

page 25...end...TSS


March 2002
Livestock Mortalities:
Methods of Disposal and Their
Potential Costs

snip...

The estimates of livestock mortalities used throughout this report are
believed to not include most “downer livestock”, many of which are
currently processed into human food at specialized slaughter facilities.
The number of downer livestock in the US is unknown, but estimates put the
number as high as 1.5% of all cattle, or nearly 1.8 million cows per
year (National Market Cow and Bull Audit).

snip...

http://www.renderers.org/economic_impact/MortalitiesFinal.pdf


To be published in the Proceedings of the
Fourth International Scientific Congress in
Fur Animal Production. Toronto, Canada,
August 21-28, 1988

Evidence That Transmissible Mink Encephalopathy
Results from Feeding Infected Cattle

R.F. Marsh* and G.R. Hartsough

•Department of Veterinary Science, University of Wisconsin-Madison, Madison,
Wisconsin 53706; and ^Emba/Creat Lakes Ranch Service, Thiensville, Wisconsin
53092

snip...TSS

OBSERVATIONS AND RESULTS

A New Incidence of TME. In April of 1985, a mink rancher in Stetsonville,
Wisconsin reported that many of his mink were "acting funny", and some had died.
At this time, we visited the farm and found that approximately 10% of all adult mink were
showing typical signs of TME: insidious onset characterized by subtle behavioral
changes, loss of normal habits of cleanliness, deposition of droppings throughout the pen
rather than in a single area, hyperexcitability, difficulty in chewing and swallowing, and
tails arched over their _backs like squirrels. These signs were followed by progressive deterioration of neurologic function beginning with locomoior incoordination, long periods
of somnolence in which the affected mink would stand motionless with its head in the
corner of the cage, complete debilitation, and death. Over the next 8-10 weeks, approximately
40% of all the adult mink on the farm died from TME.

Since previous incidences of TME were associated with common or shared
feeding practices, we obtained a careful history of feed ingredients used over
the past 12-18 months. The rancher was a "dead stock" feeder using mostly (>95%) downer
or dead dairy cattle and a few horses. Sheep had never been fed.

snip...

http://www.bseinquiry.gov.uk/files/mb/m09/tab05.pdf

> Concerning disposition of nonambulatory cattle, Milian-Suazo et at.
> (10) reported that more than one-half of nonambulatory cows were
> culled in the same lactation, it has also been reported that some mink
> ranchers have contracts with local slaughter plants to pick up
> nonambulatory or dead cows (8). The entire carcass is reportedly
> ground into feed at the mink facility.


WONDER how many cattle ranchers were using this same
practices of grinding the entire carcasses of there
downers and using for feed?


TSS

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