In African countries, the diversity of domestic animals is maintained thanks to traditional agro-pastoral communities. The mutations experienced by these communities result in an erosion of the genetic diversity of which they are the guardians. In response to threats to biological diversity, a convention for its protection was signed in 1992 by several countries, including Niger, therefore committed to conserving the genetic diversity of its livestock breeds. One of these breeds, the Koundoum sheep, is threatened with extinction. The objective of this work is to study the reasons and consequences of this decline, through semi-structured interviews with 104 sheep farmers in the natural habitat of Koundoum. The main reasons given as causes of the decline in the numbers of Koundoum sheep are crossbreeding with other breeds (25.00%), the lack of pasture on the banks of the Niger River (19.23%) and mortality linked to parasitism. (15.38%). Regarding the consequences, this regression was considered damaging for national biodiversity by 7.69% of breeders. 14.42% of breeders think that it is a loss of local cultural values ​​and 9.62% see it as a risk loss of a breed adapted to their land. 42.31% of herders perceive this disappearance primarily as a loss of financial resources. In short, the farmers' responses refer to two distinct phenomena: substitution between breeds and the decrease in the total sheep population in the area. The two phenomena call for different conservation strategies, in situ and ex situ. These should be integrated into a global program involving breeders, scientists and political authorities.