3. ORIGIN OF SHEEP AND SHEEP PRODUCTION METHOD IN ARGENTINA

3.1 The origin of sheep in Argentina

The sheep of Argentina were derived largely from Europe commencing in the XVIth century. Significant imports, including from Great Britain, followed in the XIXth century, a time when scrapie was well known in some of the exporting countries. However, at this same period exports from Europe, especially Great Britain were made to Australia, New Zealand, South Africa and North America. None resulted in reports of scrapie in their new location. The reason for the non-occurrence of scrapie may just have been good fortune but more likely it was due to breed selection. Merinos from whatever source, Romney Marsh from Kent in England, Corriedale and Lincoln are seldom or never reported to have scrapie. Some other breeds from Great Britain were not suited to Argentine conditions and were culled. Black-faced sheep, such as the Suffolk, were not favoured because in Argentina the black wool diminished the value of the fine wool fleeces which was the raison d’être for the Argentine sheep industry.

Scrapie has never been recorded or reported in Argentina nor in any breeding sheep exported from Argentina to other countries without scrapie. According to Parry (1993) who had a specialised knowledge of Suffolk sheep scrapie, countries which imported sheep which subsequently developed scrapie were mostly of the Suffolk breed but with some incidents in Cheviots and Dorset and Hampshire breeds. However, none of these were favoured by Argentinean importers. Australia (in 1952) and New Zealand (in 1952-1954 and 1976-1977) imported Suffolk sheep that developed scrapie but in each case eradication was achieved by draconian slaughter of all affected and in-contact stock. The disease has never reappeared. By contrast Suffolk sheep imported into the USA from Great Britain, some via Canada, and reared intensively developed scrapie (USDA, 1991). Moreover, the disease has spread and has been difficult to control and eradicate. The majority of cases in the USA have been in Suffolks (88%). This breed which is strongly associated with the introduction of scrapie into countries previously free of the disease, has no importance in Argentina.

Parry, (1993) provided a list of breeds in which scrapie has or has not been found. Gordon (1966) and later, Pattison (1972) reported the famous 24 breed experiment. A variety of British sheep breeds were experimentally challenged with scrapie by the efficient intracerebral route of inoculation. There was a considerable variation in the incidence of disease between breeds as a result. At the time of these two reports the influence of the PrP gene on disease occurrence was unknown. In the 24 breed experiment scrapie negative animals could have been due to the unknown presence of resistant (long incubation period) alleles. Nevertheless, because between 30 and 57 sheep of each breed were inoculated, the experiment may have given some indication of the prevalence of such alleles should they have been responsible for the resistance to scrapie. Certainly, the results of these two studies fit well with the observations from Australia, New Zealand and Argentina that some breeds may be less likely to develop scrapie than others, even when imported from countries with scrapie.

Currently, the main breeds of sheep in Argentina are Merinos, mostly of Australian origin, Corriedale, Romney Marsh and crosses with Lincolns (APPENDIX A). Since 1990, there has been no importation of live breeding sheep into Argentina from a country that has reported the occurrence of scrapie to the OIE. Before this time, breeds were selected that have fine wool, white faces and points, and in which scrapie had either never been recorded, or was rare. In any event no scrapie case has ever been recorded or reported in Argentina.

3.2 Sheep production systems

Historically, with no known occurrence of scrapie, the Argentinean national sheep flock is regarded as having a low risk of harbouring scrapie. Importation criteria (see below) maintain the risk of scrapie introduction to a low level.

Endogenous risks of scrapie transmission are low for a number of reasons:

• The system of feeding is extensive and limited only to grass and conserved food.

• Concentrates are not fed so cross-contamination of sheep diets by pig and poultry feed containing MBM is impossible.

• The sheep management system is pyramidal with nucleus breeders at the top, who sell breeding stock to multipliers, who in turn sell stock to commercial flocks. This means that sheep movements are mainly limited and in a vertical direction within breed. All pedigree sheep are individually marked by tattoo in a white ear that aids subsequent identification. All identification numbers are recorded in the Stock Book initiated by the Breeders Association in 1896.

• Since 1937 flocks are also registered with the Rural Society in a Flock Book and the records are supervised by SENASA. This means that tracing the parentage of the sheep is possible if scrapie occurred. Also reporting would be encouraged, because the integrity of the Stock Book is paramount.

• The stocking rate is low, or very low, particularly in Patagonia (< 1 sheep /2 Ha).

• Because the sheep industry is currently geared predominantly to fine wool production for export, castrated male animals dominate and are kept to and old age, 7 or 8 years. Being male animals they present a low risk for scrapie transmission (no placenta), are not stressed by pregnancy, lactation or lamb rearing and so present an ideal population for monitoring and surveillance for scrapie.

• The sheep population is in decline from a total of 75 million in 1875, to less than 14 million in 1998 (APPENDIX A).

• Twice yearly inspections of sheep for FMD surveillance and blood collection by trained staff means that any occurrence of scrapie is likely to be detected; none has. Further inspections are done as part of the programme for sheep scab control.

• There is virtually no sheep-dairy industry, and therefore no incentive to feed concentrates.

• The main product from sheep is wool. Most sheep are killed for human consumption on farm. Waste from such enterprises is buried on farm and does not form a source for MBM.

• Some sheep are slaughtered in abattoirs where there is always ante-mortem inspection for evidence of scrapie and other diseases by SENASA-trained veterinary staff. All sheep are forced to stand so that gait ataxia and downers can be detected. In these abattoirs waste is rendered but MBM has never been recycled to sheep and is, since 1995, prevented by law from being fed to any ruminant species. It is instead used to feed poultry, pets and pigs.

The future of the sheep industry is uncertain. Some diversification to meat production is occurring but the national flock is declining in size.

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