Radical view of BSE demise
By Shelley Wright
SLAUGHTERING 44,000 cattle would be as effective at speeding up the eradication of BSE as MAFFs plan to cull 127,000 animals, according to a new report.
Scientists at Oxford University, along with MAFF experts, analysed the incidence of BSE, using the latest computer models. And they concluded that, without any slaughter policy, the disease will be almost extinct by 2001.
The report, published in Nature, says the number of cattle infected with BSE through contaminated feed has been negligible since 1994. Any cases of BSE in animals born since then must be due to maternal transmission, it concludes.
Recent MAFF trial results showed a 10% rate transmission from cow-to-calf. Using that figure the scientists predicted there will be 6950 cases between 1997 and 2001. And they then compared 14 possible culling policies to see what effect they would have on speeding the eradication of the disease.
MAFFs policy of targeting cohorts of BSE cases born between Oct 15, 1990, and the end of June, 1993 would involve the compulsory slaughter of 80,000 cattle. In addition, MAFF proposes a voluntary cull of cohorts in the 1989/90 birth year, bringing the total to a maximum of 127,000 cattle.
That policy, say the scientists, will prevent 1580 future cases of BSE, or 23% of the expected cases between 1997 and 2001. But 80 cattle would be destroyed for every one case of BSE prevented.
But the scientists say 1490 future cases, or 21% of the expected cases, can be eliminated by culling 44,000 cattle at most. That would prevent one case of BSE in every 30 animals slaughtered. And that figure also takes account of maternal transmission, which MAFFs current policy does not.
The report says that the similar results can be achieved with many fewer animals because of better targeting. Instead of culling all cohorts, the new option would only slaughter cohorts in herds that had suffered more than 1 case per 27 cattle.
From their analyses of past trends, the scientists found that this was the most efficient way of targeting future cases of the disease – with effiency measured as the largest number of BSE cases prevented for the minimum number of cattle slaughtered. But the report also cautions that "the practicalities of such an approach, given that roughly 25,500 herds would be affected, needs careful consideration".
MAFFs plan would involve 6240 holdings although that would rise to up to 31,000 herds if the EU forced it to increase the cull to take account of maternal transmission. *
Comparison of possible culling policies
Cases savedTotal cattle culledCattle culled
No of originper case
2.All cattle born before 7/8825040.35m3.8 111,0001,400
3.All cattle born10/90-6/933,600512.03m22 111,000564
4.All cattle born in herds from which case originated during 1/91-12/956,300902.87m3128,500455
5.Cattle born in the 10/90-6/91,7/91-6/92 or
7/92-6/93 cohorts in herds from which a case originated
in the corresponding cohort during 1/91-12/95
6. As 5, but extended to include 7/89-9/90 cohort(govt compulsory + voluntary policy1,58023127,0001.46,24080
7. Cattle born in 7/89-6/92 in herds with more than 1case in that cohort range (during 1/91-12/95) per 27 cattlein the holding6911021,3000.2363831
8. As 7, but with threshold of 1 case per 50 cattle1,4202071,9000.772,00051
9. Cattle born after 10/90 within 6 months of BSE casein the dam79711<22,0000.24 22,00028
10. Cattle born after 10/90 within 12 months of BSEcase in the dam1,10022<44,0000.47 35,60040
Combined herd-targeted and maternally-targeted policies
11. Policies 7 + 9 combined1,49021<44,0000.47 25,50030
12. Policies 8 + 9 combined2,20032<94,0001.0 26,80042
13. Policies 5 + 9 combined1,45021<53,0000.57 26,30037
14. Policies 6 + 9 combined2,38034<150,0001.6 31,00063
Source: Nature, Aug 29 1996.