SMALL RUMINANT PRODUCTION IN EUROPE : STATE OF THE ART AND MAJOR CHALLENGES WITH FOCUS ON OUTDOOR ACCESS AND PARASITE INFECTION. 

Hervé HOSTE1, Christophe CHARTIER2 
1 UMR 1225 INRA DGER,  ENVT. 23, Chemin des  Capelles, 31076 TOULOUSE Cedex.
2 AFSSA LERC 60, rue de Pied de Fond, 79012 NIORT Cedex

Compared to pig or poultry productions, the conversion from conventional to organic farming (OF) systems probably affects less the small ruminants, because the mode of production throughout Europe is generally  based on  outdoor grazing. This means that the presence of endoparasites associated with grazing has long been known as a major challenge in small ruminant production. In conventional systems the usual mode of control of helminths relies mostly on an intensive use of chemical anthelmintics (AHs), at strategic times depending on the epidemiology of  parasites. The emphasis on non chemical prevention in OF, restricting the number of treatments per year, means that other strategies have to be evaluated and implemented in order to avoid or, at least, to  severely reduce the use of chemical drugs. Three main basic concepts can be applied to prevent parasite infections and/or to maintain the intensity of infection under a  threshold  compatible with production. These approaches concern either the free living stages in the environment  or the host parasitic stages: 1/ To avoid or to reduce the contact between the host and the infective stages of parasites. 2/ To reinforce the host response against the parasites in order to limit the negative effects of parasitism on animal health and production. 3/ To kill the parasites within the host and consequently reduce the contamination of environment with parasitic eggs.

For the 3 main classes of endoparasites which  infect the small  ruminants (nematode, cestode and trematode), most of the results on non chemical methods of control have been acquired concern on the nematode infection,  particularly those of the gastrointestinal (GI) tract. This is due to the fact that resistances to AHs in nematodes are nowadays a major  issue in conventionally reared small ruminants whereas this is less the case for flukes and cestodes. AH resistance has thus deeply stimulated the seek for non chemical options to control GI nematodes. These results will be used as an example to illustrate the 3 different concepts.
 
1. Non chemical methods targeting the free living stages of parasites.
•	Grazing management 
It has been known for long that an efficient pasture  management, aiming at a low pasture infectivity, can strongly complement  the control of   parasitic nematodes  relying on strategic AH use.  Three strategies of pasture managements have been described:  prevention, evasion and dilution of the risk represented by the third stage infective larvae, the latter method (dilution) including mixed grazing between different host species (Michel 1985). In OF systems, these solutions,  relying  on the rational use of pastures, should be the cornerstone  of the prevention against the parasitic risk, the  use of  natural, or, if necessary, chemical AHs to cure animals  being only considered as a complement to a relevant management of pastures. Methods aiming at assessing the  diagnosis  of flock  parasitism based on the analysis of management systems are currently evaluated. However, the optimal modes of management for parasites have first to be compatible with the objectives related to animal nutrition and forage production 

•	Biological control with  nematophagous fungi.
This method of control mainly refers to the work dedicated to Duddingtonia flagrans. This fungus has two main valuable properties. First, the ability to kill the nematode larvae. Second, the ability of the fungi spores to survive passage through the digestive tract after ingestion by animals, enabling the viability and activity of fungi against the larvae in faeces. Several studies both in controlled and field conditions in sheep or goats have illustrated the effectiveness of daily spore distribution to significantly reduce the larvae in faeces and consequently the pasture contamination (Larsen 1999). However, some limits still exist before commercialisation, in particular the need to develop an effective mode of  long term delivery of the spores. 

2. Improving the resistance and the resilience
of the  infected host
To date, vaccines against nematodes are not available. The current researches are mainly dedicated to a molecular approach  but major technological barriers still exist before the design of a recombinant vaccine. The genetic selection of hosts, resistant to parasites represent an other option to limit the nematode populations (selection for resistance) or their pathological consequences (selection for resilience). Such   programmes of within breed selection for resistance to GI nematodes exist for some highly productive breeds. They have made good progress but have also identified some potential hurdles in the concept. On the other hand, a limited amount of data has been collected on the value of genes from the local breeds as promoted by OF rules. The last option to improve the host response to parasitism is represented by the possibility to manipulate the host nutrition, in particular by reference to the  scarse nutritional resources (Coop and Kyriazakis, 1999). Strategic supplementations to young animals and/or periparturient ewes or goats have proven to be effective, but  further researches are still needed to measure more precisely the deficits due to parasite infection in order to better adapt the supplementation to cover the additional requirements in infected hosts.  

3  Targeting  the  worm populations in the host
•	Plant anthelmintics.  
For health management, the OF rules recommend to prefer the use of plant preparations or homeopathy to  chemical treatments.  Plant preparations have represented  the traditional way to treat human and animals  for several centuries. They still remain largely used in some parts of the world. The interest in their potential use is currently expanding, but  scientifically-based studies to confirm  the claimed efficacy of these plant preparations are usually lacking. Moreover, the regulation in their use in regard of the key questions of residues or human safety will have to be addressed. 
   
•	Nutraceuticals
This refers to forage or fodders which are used first as a rich source of bioactive products that can operate  to the health benefit of herbivores rather than for their nutritional values. Amongst those, tannin-rich plants have attracted most attention for their effect on GI nematodes in ruminants. However, some favourable data have also been acquired with plants whose tannin content is low, like chicory. In both cases, negative effects on parasite biology and positive consequences on host resilience have been reported. However, they vary depending on the species of plant, parasite and host. Therefore, before relevant implementation use in organic farming systems, more research is required to better understand the mechanisms of action. In particular, to determine what are the active plant components and whether they act through direct antiparasitic effect or indirectly by increasing host resistance (Hoste et al, 2005). 

Conclusions A “basket of options”, with pros and cons identified, can contribute to control  nematodes in small ruminants. However, it is clear from previous experience, that the only way to achieve a sustainable control, compatible with  OF rules, will have to rely on an integrated approach, combining several solutions, the grazing management strategies being central in these control schemes. 

References
Coop, R.L., Kyriazakis,  I., (1999). Nutrition parasite interaction. Vet. Parasitol. 84, 187-204.
Hoste H., Jackson F., Athanasiadou S., Thamsborg S., Hoskin S. (2006). The effects of tannin rich plants on parasitic nematodes in ruminants.Trends Parasitol (in press)
Larsen M. (1999) Biological control of helminths Int J Parasitol 29, 139-146.
Michel JF (1985) Strategies for the use of anthelmintics in livestock and their implication for the development of drug resistance Parasitology 90, 621-628.

The authors acknowledge  the financial support from the European Union (Contract WORMCOPS, No QLK5-CT 2001-01843)