Pedigree Holstein-Friesian herd of 55 cows

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FINAL REPORT ON BSE CONFIRMED IN AN ANIMAL BORN ON 3 OCTOBER 2001 & TWO COHORT ANIMALS BORN ON 28 SEPTEMBER 2001 & 1 MAY 2002 IN A PEMBROKESHIRE HERD
BACKGROUND

BSE was confirmed in a homebred pedigree Holstein Friesian cow born on 3
October 2001. This case was identified in the survey of emergency
slaughtered Over Thirty Months Scheme (OTMS) animals and came from a
dairy herd in Pembrokeshire, South West Wales.

The animal calved in January 2004, was dried off in November 2004 and was
due to calve again in late January 2005. The animal was housed in early
January 2005 when the owner noticed that it was in poorer condition than the
other dry cows. A few days after housing the animal was found recumbent in
the building with its hindlegs splayed and only managed to rise with difficulty.
The animal remained unsteady on its hindlegs and the owner disposed of it as
an emergency slaughtered OTMS animal on 17 January 2005 aged 39
months and 14 days.

Defra received the initial positive BioRad ELISA test result for this case on 21
January 2005. The case was confirmed on 1 March 2005 following a positive
Western Blot result and detailed further investigations.

Thirty-nine cohort animals 1 and one offspring animal (born January 2004) were identified and effectively restricted within 24 hours of suspicion of the
index case. The cohort and offspring animals were slaughtered following
confirmation of the index case. Thirty-four cohorts were slaughtered in an
OTMS abattoir on 12 May 2005. The offspring animal and five of the cohorts
were slaughtered on farm. All the cohort animals were tested for BSE. Two of
the animals slaughtered in the OTMS abattoir tested positive on BioRad
ELISA. These homebred pedigree Holstein Friesian cows were born on 28
September 2001 and 1 May 2002, and were aged 43 and 36 months
respectively at slaughter. These cases were confirmed on 27 May 2005
following positive Hybrid Western Blot (2001), OIE Western Blot (both),
Immunohistochemistry (both) and Histopathology (2002) results. Where
possible, samples from the BioRad negative cohorts were also subjected to
further testing, all with negative results.

EPIDEMIOLOGICAL INVESTIGATIONS

Following the initial positive result, the State Veterinary Service carried out a
preliminary epidemiological investigation at the farm in January 2005. Defra
and the SVS carried out further epidemiological investigations at the farm in
February 2005 and May 2005.
1 Cohorts as defined in Annex I of Regulation (EC) No.999/2001, and including birth and rearing cohort animals. 17 November 2005 Page 1 of 6 Herd of Origin

A family farm owns the herd of origin. It is a 100-cow pedigree Holstein
Friesian dairy herd plus followers (173 animals registered on 3 rd June 2005). The herd was relatively young: 81% of the herd were four lactations or less at
the time of the first 2001 case. The herd has experienced previous BSE
cases. The farm occupied 150 acres until July 2001, when a further 115 acres
were purchased.

Vertical Transmission
• October 2001-born case
The pedigree dam, born in May 1999, remained alive on the farm at 25
October 2005. The grand-dam, born in November 1993, remained alive on
farm at 25 October 2005. The sire was a 1991-born Canadian pedigree
Holstein. By February 2005, this animal was reported to have sired 6 652
daughters in 1 485 herds in the UK, and 33 055 daughters in 7 987 herds in
Canada.

At 6 May 2005, three siblings of this animal, born in May 2003 (twins) and July
2004 were also alive on farm.
• September 2001-born case
The dam, born in January 1999, was slaughtered in an OTMS abattoir in
October 2002. The sire is the same as that for the October 2001-born case.
• May 2002-born case
The pedigree dam, born in December 1999, remained alive on the farm at 25
October 2005. The sire was another 1991-born Canadian pedigree Holstein.
By June 2005, this animal was reported to have sired 567 daughters in 221
herds in Canada.

Feed

The animals received colostrum from their own dams and then pooled, whole
milk. A commercial calf feed was offered during the first two months of life
and a commercial rearer was used until twelve months of age. It is possible
that, after the age of six months, some animals also received some adult
ration, on occasions when it remained uneaten by the cows.

A Cheshire mill produced the calf starter, calf rearer and adult feeds used on
the farm. The starter feed was supplied in bags (three-four per month) via a
local depot. The rearer feed and the adult feed were supplied directly from the
mill in bulk. During 2001/02, these feeds contained several imported
ingredients including:
• Maize gluten and distillers grains - from USA 17 November 2005 Page 2 of 6 • Citrus pulp - from USA/Brazil • Cottonseed Meal - from USA/Brazil • Molasses & Vegetable Oil - from USA/EU • Sunflower - from USA/Argentina • Soya - from Argentina • Copra Meal (Coconut by-product) & Palm Kernal - from
Indonesia/Malaysia • Rapeseed Meal - from UK/EU
The likely UK ports of entry for these ingredients were Liverpool, or possibly
Erith (London), Avonmouth or Portbury (Bristol) or Immingham (Hull).

Further investigation of the mill’s adult cattle ration produced between July
1998 to the end of 2002 revealed similarly sourced imported ingredients to
those listed above plus the inclusion of “fat” imported from USA/EU.

These animals were also offered a milk replacer product from the Republic of
Ireland prior to weaning, and later had access to UK produced mineral licks.
As far as can be ascertained, the milk replacer fed to these animals contained
skimmed milk powder, whey powder, palm and coconut oils, starch minerals
and vitamins. The mineral lick contained molasses, pure vegetable oil (palm
fatty acid distillate), urea and a mineral blend. As none of these ingredients
were of animal origin (other than milk) they are unlikely to be the source of
infection.

Further investigation of historic feed storage on the farm revealed that the
owner installed a new dairy in September 1998. This involved demolition of
the old dairy and feed loft, and the installation of a new adult feed bin. The
owner initially reported that the Cheshire mill was supplying adult feed at that
time. However, a further visit to the farm for an in-depth epidemiological
investigation revealed that in 1998, it was purchasing feed from a
Carmarthenshire blending plant. The farm continued to purchase from this
blending plant until January 2000, when it switched to the Cheshire mill.

On 22 July 2002, the farm purchased a new feed bin for the adult cattle. The
original emptied adult feed bin was released, tipped, moved across the
farmyard and re-erected. It was refilled with calf rearer ration from the
Cheshire mill the same day. At that time the September and October 2001
born BARB cases (aged 9 months) and the May 2002 born BARB case (aged
2 months) were all fed on calf rearer from the feed bin. The feed bin was
never cleaned out as to do so without specialised equipment presented
significant practical difficulties.

Horizontal Transmission

The herd has experienced six previous BSE cases. These were born between
1983 and 1990 with four of the six born before the 1988 feed ban. These six
cases were confirmed between 1989 and 1994.
17 November 2005 Page 3 of 6 There is approximately a ten-year gap between the birth of the 1990 case and
the 2001 case, and approximately a six-year gap between the confirmation of
the 1994 case and the birth of the 2001 case.

The herd uses standard lungworm and Clostridial vaccines prior to turnout.

Environmental Contamination

Most of the drinking water is supplied via piped troughs. There are two
streams to which the cattle have access. One rises at a neighbouring dairy
farm (14 BSE cases confirmed 1990-1994). The other rises at a beef suckler
farm (2 BSE cases confirmed 1993-1995).

There is no history of the application of waste products (abattoir waste /
sewage) to land, other than home-produced slurry/manure. There was no
evidence of the use of fertilisers containing other animal by-products. There is
no history of burying adult cattle for at least 5 years.

The farm rented land from a neighbour in April 2001, and purchased this land
in July 2001. The neighbour historically had dairy cattle (5 BSE cases
confirmed 1991-1994) but primarily kept sheep. It is likely that lambs were
buried on the former sheep land. The farm allowed winter grazing of sheep
from this flock in 2003/04 and 2004/05. The sheep were not co-grazed with
the cattle and were moved before lambing. The flock has no history of
scrapie.

Other Species

In 2001, the farm had one dog. There are now two dogs. One dog is fed just
outside the house and the other is fed in a kennel. The dry dog food is stored
in the house. Although there was no evidence of direct cross contamination,
the ingredients of the dog food used in 2001/02 were investigated. These
were poultry meal and beef tallow imported from Ireland, Netherlands and
France. The farm also has two cats which are also fed just outside the house.

CONCLUSION

The epidemiological investigation into these cases produced no evidence to
implicate vertical transmission, horizontal transmission, environmental
contamination of pasture/water etc., or access to non-cattle feed sources. A
spontaneous occurrence of BSE of genetic origin was considered unlikely
because the cases involve three different dams and two different and widely
used sires. A statistical analysis 2 of the number of herds experiencing multiple BARB cases compared to the total number of BARB cases, provides evidence
that BARB cases do not all occur by chance.

The current hypothesis for the 2001/02 cases is that these animals were
exposed to feed contaminated with the BSE agent. This is believed to have 2 John Wilesmith, personal communication 2005 17 November 2005 Page 4 of 6 been imported feed material cross-contaminated outside the UK, most likely
during trans-shipment through European ports in which mammalian meat and
bone meal (MMBM) was handled.

The EU ban on the feeding of processed animal protein (PAP) to farmed
animals did not come into force until January 2001, and some Member States
delayed effective implementation beyond this date. The new Member States
joining the EU in 2004, may also have implemented total feed controls after
January 2001.

The existence of a 1997/98 cohort cluster of BSE cases born after July 1996,
associated with two Carmarthenshire mills, and the results of the
epidemiological investigation on the farm led to the additional hypothesis that
the contaminated feed was supplied from the Carmarthenshire blending plant
in 1998 (or 1999), and the BSE agent was retained inside the feed bin until
2002.

The construction of the bin and the presence of oil contained in the feed
coating the inside of the bin would facilitate retention of infective material. The
fat-rich meat and bone meal (MBM) component of fragmented pellets is more
likely to stick to inner surfaces, and after emptying the bin, the residual
material would contain a relatively high proportion of MBM. Some of this
material would have been dislodged when the bin was moved. The first feed
drawn from the bin after movement could have contained a relatively high
MBM content 3 .
The absence of any UK BSE cases in the 2000/01 cohort provides further
evidence that historic feed carry over was responsible for these three cases.
The latest born (second 2000-born) GB BSE case in the 1999/00 cohort was
a clinical case born 1 April 2000. Northern Ireland has also had two BSE
cases born in 2000 (April and May) in the 1999/00 cohort. All these cases
were born prior to the 2001 EU feed ban.

There were no detected BSE cases on the farm in the adult cows that fed
from the feed bin between 1998 and 2002. This may be explained because:
• The overall concentration of infection in bulk feed was very low, but
there were significant pockets of infectivity. • Young cattle are more susceptible to BSE infection than adults 4 . The peak susceptibility of cattle is approximately 6 months of age. • The fat rich MBM component of fragmented pellets would be more
likely to stick to the inner surfaces of the feed bin, perhaps only being 3 As a precautionary measure the farm voluntarily ceased using the feed bin on 24 May 2005. The remaining feed was removed and disposed of on 22 June 2005, and the feed bin was
removed and destroyed on 25 July 2005. 4 Arnold et al. 2004 Estimation of the age-dependent risk of infection to BSE of dairy cattle in Great Britain. Prev.Vet.Med.66:35-47 and Supervie et al. 2004 The unrecognised French BSE
epidemic. Vet.Res.35: 349-362 17 November 2005 Page 5 of 6 displaced in significant quantities during movement of the bin. The
presence of infectivity in feed dust, may have been more pathogenic
than infection contained within entire feed pellets (possibly as a result
of direct absorption through oral or pharyngeal lesions). • By 2005, the herd was young and any adult cattle exposed to infection
may already have died. Cattle calve at 2-3 years, before they are
exposed to adult ration. The youngest (1 st lactation) animals feeding in September 1998 would have been born in 1996. By September 2005,
only 8/169 (5%) cows in the herd were born in 1996 or earlier.
The age of these three cases at detection (Sept 2001 = 43 months; October
2001 = 39 months; and May 2002 = 36 months) suggests that infection
occurred at or shortly after the bin was transferred in July 2002. This
represents an approximate incubation period (to detection) of 34, 30 and 34
months respectively.

These incubation periods are at the lower end of the reported range of 2 – 14
years (mean 60 months) for clinical cases, although only the October 2001-
born animal was showing clinical signs attributable to BSE. (The September
2001 born animal was described as having always been a “slightly nervous
cow”, although no specific BSE signs were reported). In 2005, the European
Food Safety Authority (EFSA) 5 concluded that preliminary data from UK Veterinary Laboratories Agency (VLA) cattle pathogenesis studies indicates
that BSE infectivity of the CNS occurs at ¾ of the incubation period. Further
work is underway to determine the time at which infected cattle can be
detected by routine diagnostic tests, relative to incubation period.

The preliminary results of the VLA “Attack Rate Studies” 6 (feeding varying amounts of infective cattle brain tissue to cattle) indicate that the BSE
incubation period in cattle is dose dependent. With a 100-gram dose, disease-
associated prion protein PrP sc was first detected by immunohistochemistry (IHC) at 30 months post exposure, histological changes (in one animal)
occurred at 33 months and definite clinical disease was first apparent at 35
months. With a 1-gram dose, PrP sc and histological changes were first detected at 44 months post exposure. Recent evidence 7 indicates that as little as 1mg of infective material can transmit BSE.

FURTHER INVESTIGATIONS

Samples from these cases have been included in a genetic study of BSE
cases born after July 1996 (born after the reinforced feed ban -BARB- cases).
Data from this study were presented and discussed by the Spongiform
Encephalopathy Advisory Committee in June 2005 8 . 5 EFSA Opinion on Assessment of Age Limit for SRM Removal in Cattle. 27-28 April 2005 6 EFSA Opinion on Assessment of Age Limit for SRM Removal in Cattle. 27-28 April 2005 7 Hill 2005, Review of the Evidence for the Occurrence of BARB BSE Cases in Cattle. 8 http://www.seac.gov.uk/agenda/agen300605.htm and http://www.seac.gov.uk/papers/88- 4.pdf 17 November 2005 Page 6 of 6

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