In the ruminant livestock farms, profitability speaks in favour of a strong fodder self-sufficency. This self-sufficiency seems easier to reach if the mixed farming system is diversified. However this requirement of self-sufficiency leads to a large share of forage crops (e.g., ley, leguminous meadows with seeds) in cropping plans and consequently leaves little place for cereals in straw. However, the straw resource is crucial to insure comfortable bedding for animals, and also for producing solid manure, which is often preferred to the liquid manure in organic farming. Where winters are long (4-months and more), the straw resource is often insufficient to provide the animal bedding. Organic stockbreeders thus ask their conventional neighbours to supply them with the straw that they are lacking. On the organic farms this imported, conventional straw is the transformed into manure, which is essential to ensure the organic fertility of soils and useful for the mineral fertilization of the crops. As the organic regulations authorize teh use of this "biological fertilize" since it is composted, we understand why the straw coming from conventional farms rarely returns to them. Such a use of the straw compromises the organic fertility of the conventional farms and thus leads to an ethical criticism of the practices of the biological farmers : can they leave it to the conventional farmers to produce a part of the resources they need according to modalities that their own regulations forbid ?