Saturday, August 16, 2008

A Quantitative Assessment of the Possible Role of Nonambulatory Cattle in Transmissible Spongiform Encephalopathy in the United States Mon, 6 Mar 2000

From: Terry S. Singeltary Sr. ( Subject: A Quantitative Assessment of the Possible Role of Nonambulatory Cattle in Transmissible Spongiform Encephalopathy in the United States... Date: March 6, 2000 at 1:05 pm PST

Subject: A Quantitative Assessment of the Possible Role of Nonambulatory Cattle in Transmissible Spongiform Encephalopathy in the United States... Date: Mon, 6 Mar 2000 14:15:00 -0600 From: "Terry S. Singeltary Sr." Reply-To: Bovine Spongiform Encephalopathy To: mhtml:%7B33B38F65-8D2E-434D-8F9B-8BDCD77D3066%7Dmid://00000128/!

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

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


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.

Nonambulatory 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 nonambulatory cows as nonambulatory cows represent only a small fraction of incoming rendered product,

Figure I (NOT AVAILABLE...TSS) Page 21

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 nonambulatory 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 al. (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.

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Incidence of Nonambulatory 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 I 0.6 Total 158 100.0 Totals 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, hypothetically, a potential source of TSE in the surveyed States.

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

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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.


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.


(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 Willoughby, 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.

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(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 Smitl~, R.D. 1988. Descriptive epidemiolog¥ of culling in dairy cows form 34 herds in New York state. Prev Vet Med 6:243-251.

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kind regards, Terry S. Singeltary Sr., Bacliff, Texas USA

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Thursday, February 21, 2008

TRANSCRIPT: Technical Briefing - Hallmark/Westland Meat Packing Company - (02/21/08)

Release No. 0054.08


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.


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