Genetic Diversity

Genetic diversity refers to the variety of hereditary characteristics in a species. The greater the level of genetic diversity, the better the chance a population has to cope with changing environmental conditions and survive over the long term. A larger population will usually exhibit more genetic diversity.

The BLM works to ensure that herds are in balance with other rangeland resources and authorized uses of the public lands. Maintaining this balance often requires close monitoring of the size of herds. If a herd is too small, this will inevitably lead to decreased genetic diversity and possible inbreeding. However, it is possible to manage small populations in ways that will minimize inbreeding and the loss of diversity.

Baseline data from hair samples collected during gathers can be compared between adjacent Herd Management Areas (HMAs) to determine if the herds are isolated or if genetic material is being exchanged between them. Movement of wild horses and burros from one HMA to another, whether it is from natural ingress/egress or from deliberately introduced horses, will enhance genetic diversity.

Once the BLM has established a baseline, herds are typically sampled every 10 to 15 years or every two or three gather cycles. If a particular herd shows signs of low genetic diversity, then the agency collects additional genetic information on that herd at every gather.

There are a number of management options that the BLM can consider if action is needed to address genetic concerns. These include maximizing the number of breeding-age wild horses within the herd and adjusting the sex ratio to favor intact males, which typically increases the numbers of harems and effective breeding males. Another option is to introduce one to two young mares every generation (about 10 years) from other herds living in similar environments.


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