Qualitative analysis of BSE risk factors in the United States

58 Pages·1991·2.5 MB·English

Historic, Archive Document
Do not assume content reflects current
scientific knowledge, policies, or practices.

aS F967
-563Q35
1991
Qualitative Analysis
| of
BSE Risk Factors
in the
United States
USDA-Office of Risk Assesament
and Cost-BAnaelynsise (fORiACtBA )
Room 5248 South Blig., Mall Step 3811
1400 Independence Avenue, SW |
Washington,DC 20250 ~ a
USDA:APHIS:VS
Document Delivery Services Branch
USDA, National Agricultural Library
Nal Bldg.
10301 Baltimore Blvd.
Beltsville, MD 20705-2351
United States
Department of
Agriculture
vy
National Agricultural Library |
io
Executive Summaryiaieets asia hs C202) ar seers encod | 1
Introductionintcws fcr ceca coor. Alsntes c<ccevielive tret lee <Jarises) Sins 2
Sheep Population and Practices ......... EPOEEL AR ME 3
Cattle Inventories and Practices ..........-+-++-.2--6-. 8
SldUShicl INGUSUY a) tet wemtahe cs tnie totes erate ate teste ees 13
RENGECI DINGS Var tometer tenet Pate Gost oes 515 ets «ts 15
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Executive Summary
Since 1986, Bovine Spongiform Encephalopathy (BSE) has been diagnosed in over
21,000 cattle, 0.5 percent of the United Kingdom adult cattle population or 9-10
percent of the beef and dairy operations. Almost exclusive to the United Kingdom,
new cases currently average 325-350 per week. BSE is an unconventional infectious
virus. Current hypotheses suggest that an increase in the exposure of cattle to the
sheep scrapie agent via ruminant derived proteins in feedstuffs have led to a
detectable incidence of the disease. While BSE is not known to exist in the United
States, it is of concern when considering that receipts to farmers from cattle, sheep
and related products are roughly $60 billion dollars per year and feed expenses are
over $20 billion per year.
This report contrasts the United States and United Kingdom sheep and cattle
demographics along with characteristics of the slaughter, feed, and rendering
industries. This contrast is followed by an analysis of major similarities and
differences in order to arrive at a qualitative assessment of the risk of BSE at the
national level.
Within the United Kingdom, a number of key related factors provide possible
explanations for a change in contact of cattle to sheep-derived proteins. Sheep
numbers increased by 12 million head over the last decade allowing a probable
increase in the prevalence of scrapie infected flocks. Increased sheep numbers led to
a larger amount of sheep raw material from both fallen and slaughter stock in animal
products. In addition, the adoption of a newer continuous rendering technology
process along with a drastic reduction in hydrocarbon solvents have led to changes in
the manufacturing processes.
Similarities exist in the two countries usage of continuous rendering technology and
the lack of usage of solvents, however, large differences still remain with other risk
factors which greatly reduce the potential risk at the national level.
The United Kingdom has 4 times as many sheep and 3 times as many ewes on a land
mass slightly smaller than the State of Oregon. The higher density of sheep to land
along with substantial movement of sheep is conducive to facilitating the spread of
scrapie across the sheep population. In the United States, 80 percent of the sheep are
in the 17 western States. With predators such as coyotes and large rangeland
operations, removal of fallen and diseased sheep stock to be rendered is less
complete compared to the specialized United Kingdom "knacker" industry.
The ratio of all sheep to all cattle is 32 times greater in the United Kingdom.
Likewise, the ratio of all mature sheep to all milk cows is 10 times larger. Sheep in the
United Kingdom account for 14 percent of raw rendering material versus 0.6 percent
in the United States. This computes to 3.4 pounds per dairy cow in the United
Kingdom versus 2.8 ounces per head in the United States.
Almost all cases have been in dairy herds with 89 percent of cases in cows 4 years
and older. In the United States, 53 percent of all dairy cows are less than 4 years of
age. In the United Kingdom, 70 percent of all dairy cows are older than 4 years. The
United States feeds 41 pounds per 100 pounds of milk produced versus 21 pounds in
the United Kingdom. However, for each pound of mature sheep meat and bone meal
produced, 17 tons of dairy concentrate are fed in the United States versus 0.4 tons in
the United Kingdom. The United States grows an abundance of plant based proteins.
The United Kingdom has traditionally imported some 500-600,000 tons of soybeans.
Moreover, the portion of animal proteins used as a percent of all other major feed
proteins is 6-7 percent greater in the United Kingdom.
While this qualitative analysis suggests the potential risk of BSE at the national level
is substantially less, no analysis is made of the variation in the levels of risk across
geographic areas of production. Of consideration are factors such as the
concentration of mature sheep slaughter and the proximity of rendered products from
mature sheep offal to dairy populations. A more indepth quantitative analysis of
these and other risk factors are contained in the APHIS:V S Quantitative Risk
Assessment of BSE in the United States,
Qualitative Analysis of BSE Risk Factors - 1
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Introduction
Bovine Spongiform Encephalopathy (BSE) is an unconventional infectious virus.
Virtually all cases have been in the United Kingdom with new cases currently
averaging 325-350 per week. The current hypotheses suggest that an increase in the
exposure of cattle to the scrapie agent via ruminant derived proteins in feedstuffs
have led to a detectable incidence of the disease. Key related factors provide possible
explanations for a change in the contact of cattle to sheep-derived protein. Sheep
numbers increased in the last decade suggesting a probable increase in the prevalence
of scrapie infected flocks. Increased sheep numbers led to a larger amount of sheep
raw material from both slaughter and fallen stock in rendered animal products.
Concurrently, cattle numbers trended down decreasing their contribution to total
rendered product. The adoption of a newer, continuous rendering process allowed
for lower temperature and/or shorter periods of time to be used in the manufacturing
process. In addition, the decline in the usage of hydrocarbon solvents and the
associated heat treatment used in this process potentially resulted in increased
survival of the infectious agent.
The qualitative analysis presented in this report compares and contrasts the United
States and United Kingdom sheep and cattle demographics along with characteristics
of the slaughter, feed, and rendering industries. Comparisons between the two
countries are presented at the aggregate or national level. For each sector,
background and demographic information is given followed by a section outlining key
differences between the two countries as it relates to BSE. This is followed by a
qualitative assessment which syntheses the major similarities and differences in order
to arrive at a broad estimate of risk at the national level.
Qualitative Analysis of BSE Risk Factors - 2
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