Life is good;
Elimination of our Wild Horses and Burros
Genetic Variation in Horse Populations5. **BLM Resource Notes No. 27*
NO. 27 DATE 07/20/00
By: E. Gus Cothran, PhD., Department of Veterinary Science, University of Kentucky/
The fifth in a series of 13, Session 2
*Background*One of the major focuses of conservation biology and genetic management of small populations is the preservation of genetic variability. This topic is of particular relevance to the Wild Horse and Burro Program because the majority of wild equid populations managed by the BLM are kept at population sizes that are small enough for the loss of genetic variation to be a real concern. Because a loss of genetic variability can lead to a reduction in fertility or viability of individuals in a population, it is critical that genetic considerations be included in management plans for wild equid populations. An important aspect of utilizing genetic information in management planning is an understanding of what is meant by the term genetic variation and how genetic variability can be measured in horse and burro populations.
Genetic variation is the amount of inheritable diversity in a population or an individual. It can be observed as morphological variation in size, conformation or color, but we are actually concerned with variability of genes, whether we can observe an effect of this variation or not. There are several different measures of genetic variation but two of the basic ways it is expressed are heterozygosity, the proportion of genes variable within an individual, and some type of estimate of allelic diversity, such as the total number of genetic types observed within the population. All of these different measures of variation are calculated from data collected from sampling a small set of genetic marker systems in a sample of individuals from a population. Traditionally, the genetic marker systems used to measure genetic variation in horses are a set of blood group and biochemical genetic marker systems that have been developed for parentage verification analysis of domestic horses. The blood group systems are tested by analysis of variation of antigens on the surface of red blood cells using specific antibodies and standard serological techniques. The biochemical genetic systems are serum or red cell proteins or enzymes detected by electrophoretic methods (relating to a method of separating large molecules such as DNA fragments from a mixture of similar molecules by passing an electric current through a medium containing the mixture - separation depends on each molecules electrical charge and size). Blood group testing requires a fresh blood sample with intact red blood cells. Biochemical genetic testing can utilize frozen blood or other tissues such as a muscle biopsy. At the University of Kentucky, we routinely test seven blood group and ten biochemical genetic systems so that genetic variability measures are based upon data from seventeen genetic loci.
Analysis of genetic variation in populations also is done by use of DNA genetic marker systems. In horses, these DNA systems are primarily a type of genetic marker called microsatellites. Microsatellites are highly variable sections of DNA that can be tested by use of PCR (polymerase chain reaction - a method for amplifying a DNA base sequence) and electrophoretic techniques. Direct testing of DNA can utilize almost any bodily product including hair (if the hair root bulb is present) or even feces. The estimates of genetic variation we can get from these techniques perhaps do not accurately correspond to total genomic variation, although that is not certain. However, with a sufficient comparative database, these measures can be used to determine the variation within a population as it compares to other horse populations and can be used to make inferences about the genetic health of the population at the time of sampling.
Genetic analysis of wild horse and burro populations can provide valuable information about current levels of genetic variation. This information can then be used to make predictions about how particular management strategies will influence genetic variation in the herd. Thus, genetic analysis can be a useful tool in the overall management of wild horse and burro populations on public lands.
*Contact*E. Gus Cothran, PhD. Veterinary Science, Equine Blood Typing and Research Laboratory, 101 Dimock Animal Pathology Building University of Kentucky, Lexington, KY 40546-0076 phone 606-257-3022 fax 606-257-4119 e-mail email@example.com.
DATE 08/01/00 BLM Resource Notes No. 35
Summary Recommendations - BLM Wild Horse and Burro Population Viability Forum, April 21, 1999
/by Linda Coates-Markle, Montana/Dakotas Wild Horse and Burro Specialist, Bureau of Land Management, Montana State Office/
*/The final Note in a series of 13, Session 4/*
BLM should carefully consider its mandate (The Wild Free-Roaming Horse and Burro Act) with respect to long-term genetic viability of populations of wild horses and burros.
* BLM regulations and policy state that wild horses and burros shall be managed as viable, self-sustaining populations of healthy animals in balance with other multiple uses and the productive capacity of their habitat (CFR 4700.0-6).
*Self-sustaining refers to the process whereby established populations are able to persist and successfully produce viable offspring which shall, in turn, produce viable offspring, and so on over the long term. The absolute size which a population must attain to achieve a self sustaining condition varies based on the demographic and sociological features of the herd (and adjoining herds), and these aspects should be evaluated on a case by case basis. In many cases it is not necessary that populations be isolated genetic units, but both naturally-occurring and management-induced ingress and egress activity can be considered, in order to maintain sufficient genetic diversity within these populations.
*Reproductive capacity is, to a large degree, dictated by the genetic fitness of a population. Generally speaking, the higher the level of genetic diversity, within the herd, the greater its long-term reproductive capacity. Inbreeding, random matings (genetic drift), and/or environmental catastrophes can all lead to the loss of genetic diversity within the population. In most herds, though, genetic resources will tend to be lost slowly over periods of many generations (~10 years/generation), and there is little imminent risk of inbreeding or population extinction. Potential negative consequences of reduced diversity, however, may include reduced foal production and survival, as well as reduced adult fitness and noted physical deformities. Smaller, isolated populations (<200 total census size) are particularly vulnerable when the number of animals participating in breeding drops below a minimum needed level. This minimum level can be calculated and is different for each population (see subsequent recommendations).
BLM should continue to use (and improve upon) defensible scientific aerial and/or ground survey techniques in census activities for all managed wild horse and burro herds. In order to fully evaluate genetic viability issues, populations which participate in a measurable level of natural ingress or egress activity and which are, in reality, a component of larger metapopulations, should be identified, and the genetic impact of this activity should be estimated. *EXISTING POLICY:* BLM regulations and policy state that HMAs should be inventoried and monitored for population size, animal distribution, herd health and condition and habitat characteristics at least every 4 years (CFR 4710.2). As such, BLM is required to provide reliable estimates of population size and distribution within each herd management area on a regular interval.
Metapopulation refers to two or more local breeding populations which are linked to one another by dispersal activities of individual animals. These populations may have unique demographic features (birth and death rates) but ultimately may share some genetic material if interbreeding is occurring between individuals. This sharing of genetic material may act to enhance genetic diversity within participating herds, and as such, these populations should be evaluated as one larger metapopulation.
A complete population census of each herd management area is unrealistic, especially for the larger populations (>200 total census size). However, population size can and should be estimated using reliable scientific techniques. These survey techniques are under continual revision and BLM continues to participate in these research efforts. On a more critical level, however, is the determination of size of the many smaller populations (<200 total census size) over which BLM has responsibility. Available data indicates that almost 70% of the managed herds have AMLs (appropriate management levels) set at 150 animals or less. In fact, almost 40% of the herds in Nevada, Utah, Wyoming, Colorado, and Arizona (71 out of 177 total HMAs) are indicated to have population sizes of less than 50 animals. There is a real possibility that some of these populations will be unable to maintain self-sustaining reproductive ability, over the long term, unless there is a natural or management induced influx of genetic information from neighboring herds. An exchange of only 2 to 3 breeding age animals (specifically females), every 10 years, is often sufficient to maintain genetic diversity within a given herd. Estimates of existing genetic diversity can be calculated for each wild horse and burro population (see subsequent recommendations).
BLM should establish baseline genetic diversity information for each population over which it has management responsibility. *EXISTING POLICY:* BLM regulations and policy state that HMAs should be inventoried and monitored for population size, animal distribution, herd health and condition and habitat characteristics at least every 4 years (CFR 4710.2). Furthermore, the purpose of monitoring is to collect data necessary to evaluate progress (or lack thereof) in achieving the objectives of management. Within the context of wild horse and burro populations, the ability to maintain the quality of “reproductively self sustaining” is required. This can primarily be accomplished through evaluation and the maintenance of an acceptable level of genetic diversity within the population over the long term.
Establishing baseline genetic diversity, for a wild horse population, often refers to typing up to 29 genetic marker systems from a sample of individual animals (~25 individuals or up to 25% of the population) within a specific herd. Traditionally, these marker systems have included blood group and biochemical systems, and have required fresh blood samples. These systems were originally developed for verifying parentage or founder animals within a herd. Analysis of genetic diversity, however, can also be done through the use of DNA genetic marker systems, and direct testing can utilize almost any bodily product including hair or even feces. Only DNA marker analysis can be used for burros, however, due to the very limited variation in blood protein genes.
Most wild horse herds, sampled to date, have shown fairly high levels of genetic diversity. In some cases, however, this diversity is attributed to a large number of low frequency and relatively rare genetic material which is often easily lost from the herd. Thus, it becomes important to understand the genetic makeup of individual herds. Baseline data needed to establish current levels of genetic diversity in populations is relatively easy to gather. Individual samples cost about $25 to process, and if ~25-50 individuals are sufficient to establish baseline information for herds ranging in size from 100 to 200 animals, then the cost would be approximately $1250 for herds of this size. As a result, a comparison of genetic viability levels in the tested population can be made to existing information from over 100 domestic and wild horse populations representing different herd sizes and demographic backgrounds.
BLM should establish a realistic management goal for maintenance of genetic diversity within all managed populations. Previous wildlife conservation research, and current efforts with wild horses, suggest management should allow for a 90% probability of maintaining at least 90% of the existing population diversity over the next 200 years. Existing diversity should be sufficient to ensure a self-sustaining (see earlier definition) reproductive capacity within the herd.
BLM regulations and policy state that wild horses and burros shall be managed as viable, self-sustaining populations of healthy animals in balance with other multiple uses and the productive capacity of their habitat (CFR 4700.0-6). By definition this requires BLM to manage to allow established populations to successfully produce viable offspring which shall, in turn, produce viable offspring, and so on over the long term. This suggests that management monitor levels of genetic diversity within the population in order to mitigate the effects of genetic drift and possible inbreeding and population-associated problems due to loss of diversity.
Genetic diversity, within wild horse and burro populations, refers to the entire complement of genetic material representative of all individuals (or a sample of individuals) from within the population. Some populations may possess genetic uniformity to a certain “type” or breed of horse, but management interests are specific to maintaining a maximum diversity of genetic material which appears representative of each herd. Promotion of diversity will minimize the effects of genetic drift, or the random loss of genetic material due to mating processes, and maximize genetic health of the herds.
Once baseline genetic data has been established, the main focus of genetic management, especially for the smaller populations (<200 total census size), becomes the attempt to preserve as much of the existing genetic diversity as possible. Establishing a genetic conservation goal will require re-testing of herd diversity on at least a five-year cycle, with subsequent evaluations of the potential impact of management decisions (including the establishment and/or revision of appropriate management levels) on that diversity. Management may need to evaluate ways to introduce genetic material into a herd which appears genetically deficient in order to be self-sustaining over the long-term (see subsequent recommendations). Baseline genetic data can also be incorporated into PVA (population viability analysis) models, which attempt to predict the impact of management decisions (as well as environmental catastrophes) on existing diversity levels. Most models require reasonably accurate data in terms of age class foaling and mortality rates, as well as individual genetic information. As such, the means to collect accurate data necessary for a genetically-based PVA, for most herds, is probably unavailable at the present time.
BLM should, in its efforts to evaluate the genetic diversity and self sustaining nature of managed herds, estimate the genetic effective population size (Ne) of all populations, or metapopulations, with a total census size of 200 animals or less.
*BLM regulations and policy state that wild horses and burros shall be managed as viable, self-sustaining populations of healthy animals in balance with other multiple uses and the productive capacity of their habitat (CFR 4700.0-6). By definition this requires BLM to manage to allow established populations to successfully produce viable offspring which shall, in turn, produce viable offspring, and so on over the long term.
The genetic effective population size (Ne) is a measure of the total number of mares and stallions which contribute genetically, through successful breeding, to the next generation. Although no standard goal for Ne currently exists for wild horse and burro herds, a goal of Ne=50, which comes from domestic breeding guidelines, can be conservatively applied. Populations, where Ne is calculated to be less than 50, may experience higher rates of loss of genetic diversity than would be considered acceptable under recommended management goals (see earlier recommendation).
Limited research into wild horse herds (Pryor Mountain Wild Horse Range and Assateague Island National Seashore populations) has demonstrated that the “Ne”, for a herd under a natural age structure, is about 30-35% of the total census population size. In other words, a total population size of about 150 animals might support only a minimum (Ne=50) genetic effective population size. Ne, however, is difficult to calculate for wild horses, since the calculation is complicated by a number of issues. The harem structure of the population, for example, greatly limits male participation in breeding, creating an uneven ratio of breeding sexes which reduces Ne and contributes to a high variation in individual reproductive success. Extreme fluctuations in population size, due to the effects of removals, can also act to reduce the value of Ne. Ne is also highly influenced by the sex ratio and age class structure of a population. A sex ratio which favors males and results in larger numbers of smaller sized harems, within the herd, will act to increase Ne (and male participation in breeding) to a point. A population with an age structure involving high numbers of young animals (<5 years of age) will have a lower value of Ne than a similar sized population with a larger component of older breeding-age animals (>5 years of age). Also, there is no single, uniformly accepted method to calculate Ne. However, researchers have used and applied several formulas to certain wild horse herds and have found this comparative approach to provide the best estimates. Generally, the best possible data on population sex ratios and age structures, coupled with reasonable estimates of foaling and mortality rates, will enable managers to evaluate the genetic health of most herds.
BLM should evaluate viable management alternatives for conserving or enhancing genetic diversity within populations (or metapopulations) having a known limited level of diversity, a total census size of less than 200 animals and/or an estimated genetic effective population size (Ne) of less than 50.
BLM regulations and policy state that wild horses and burros shall be managed as viable, self-sustaining populations of healthy animals in balance with other multiple uses and the productive capacity of their habitat (CFR 4700.0-6). By definition this requires BLM to manage to allow established populations to successfully produce viable offspring which shall, in turn, produce viable offspring, and so on over the long term. This suggests that management monitor levels of genetic diversity within the population in order to mitigate the effects of genetic drift and possible inbreeding.
Viable management alternatives for conserving genetic diversity within managed wild horse and burro herds may take several forms. Some options to be considered might include: altering population age structure (through removals) to promote higher numbers of reproductively-successful animals; altering breeding sex ratios (through removals) to encourage a more even participation of breeding males and females; increasing generation intervals (and reducing the rate of loss of genetic material) by removing (or contracepting) younger versus older mares; and/or introducing breeding animals (specifically females) periodically from other genetically similar herds to help in conservation efforts. In this last scenario, only one or two breeding animals per generation (~10 years) would need to be introduced in order to maintain the genetic resources in small populations of less than 200 animals.
Simply increasing the total herd size by adding additional animals (adjusting the management AML upward) is not the only viable technique for enhancing the genetic effective population size (Ne) of a wild horse and burro population. With sound knowledge of existing herd demographic information, management alternatives for specific populations can be evaluated through research modeling efforts. As such, management also has the option of adjusting certain aspects of herd structure in order to promote genetic conservation. Major options for consideration were presented in the above definition. It should also be noted that any adjoining herds, which are naturally participating in an exchange of animals and genetic material through interbreeding, are probably self-maintaining their genetic diversity and management should consider both supporting and estimating this type of activity.
BLM should continue to evaluate incidences of club foot and parrot mouth, and other such physical deficiencies, within individuals of wild horse and burro populations, on a case by case basis. Currently, there is no solid evidence that these physical conditions are purely genetically-based and that they may contribute to a long-term loss of genetic health in the herd.
BLM regulations and policy state that HMAs should be inventoried and monitored for population size, animal distribution, herd health and condition and habitat characteristics at least every 4 years (CFR 4710.2). Furthermore, the purpose of monitoring is to collect data necessary to evaluate progress (or lack thereof) in achieving the objectives of management.
Physical deficiencies may be encountered at different rates for different wild horse and burro herds. Conformational deformity and/or misalignment is often expressed in the legs, feet and mouth but may be apparent in other structural areas as well. Despite the existence of a specific deficiency, however, an individual animal may otherwise be healthy, bear acceptable condition and be fit enough to contribute socially and genetically to the herd. If an individual animal is successful in these merits, there seems little reason to remove it simply on the grounds of physical imperfection by human standards.
These types of physical deficiencies are thought, by researchers, to potentially be both genetically and environmentally (poor forage base during fetal development) induced. As such, efforts to remove individual animals bearing this condition from herds may or may not result in a significant loss of expression of that trait from the herd. Success in this area will be related to the source of the genotype and whether it results from inbreeding, founder effect, and/or genetic drift. However, since multiple genes are probably responsible for the expression of these traits, it is likely that the genetic predisposition will remain in the herd despite the fact that minimal expression is observed. Eventually over time, then, the trait may continue to reappear. Future research may illuminate different theories regarding this situation. In the meantime, the impact of human-induced selection, over factors of natural selection, should be evaluated carefully and with due consideration as to the possible long-term impacts on individual herds. In other words, if the animal is otherwise healthy, maintaining a status within the social structure of the herd, and contributing to the gene pool through successful breeding, it might be left on the range. However, if a population excess has been determined, and an individual animal is young and has yet to contribute to the gene pool, it may be a candidate for removal and adoption or sanctuary-placement. Likewise, if the animal is older, less healthy, and has withdrawn from the herd, it may also be a candidate for removal with sanctuary placement.
BLM should continue to manage wild horse and burro herds, beneath the level which is scientifically referred to as the ecological carrying capacity (EEC) of the population. This is the level at which science has determined that density-dependent population regulatory mechanisms would take effect within the herd. Most herds are currently managed close to their “economic carrying capacity” which is approximately 50-65% of EEC. At this level of management, health of both the horse herd and range ecosystem are prioritized.
BLM regulations and policy state that wild horses and burros shall be managed as viable, self-sustaining populations of healthy animals in balance with other multiple uses and the productive capacity of their habitat (CFR 4700.0-6). Thus appropriate management levels (AMLs) are established which provide for a level of use by wild horses and burros which results in a thriving natural ecological balance and avoids deterioration of the range. Furthermore, proper management requires that wild horses and burros be in good health and reproducing at a rate that sustains the population and that population control methods be considered before the herd size causes damage to the rangeland.
Ecological carrying capacity (EEC) of a population, is a scientific term which refers to the level at which density-dependent population regulatory mechanisms would take effect within specific herds. At this level, however, the herds would show obvious signs of ill fitness including poor individual animal condition, low birth rates, and high mortality rates in all age classes due to disease and/or increased vulnerability to predation. In addition, supporting range conditions would be noticeably deteriorated, with much of the available habitat showing symptoms of irreparable over-grazing.
Populations of wild horses on western rangelands have the capacity for rates of increase as high as 20-25% per year. Recent research has shown that unmanaged populations of wild horses and/or burros might eventually stabilize (due to density-dependent regulatory mechanisms) at very high numbers, near what is known as their food limited ecological carrying capacity. At these levels, however, the herds would show obvious signs of ill-fitness including poor individual animal condition, low birth rates, and high mortality rates in all age classes due to disease and/or increased vulnerability to predation. In addition, supporting range conditions would be noticeably deteriorated, with much of the available habitat showing symptoms of irreparable over-grazing. Most wild herds are currently managed close to economic carrying capacity which allows the herds to be healthy with strong foal production and high individual survival rates. This approach should be continued, as it benefits the populations and also allows for the maintenance of healthy and in-balance rangeland systems.
Montana State Office, MT-010, Billings, Montana
phone (406) 896-5223, fax (406) 896-5281
(*Areas including those listed as AML zero but which had wild horses and burros in 1995.)
THE NUMBERS-THEN AND NOW and HOW the BLM MANIPULATES THE TRUTH:
(The Act is the Law-Public Law 92-195)
Given this perspective, it seems prudent to recommend that at least 100,000 wild horses and burros be allowed to occupy the Western public lands in all their legal herd areas existing in 1971, as is spelled out in the law. This would more truly fulfill the mandate of the Wild, Free-Roaming Horse and Burro Act (PL 92-195) to preserve wild horses and burros. The Wild and Free-Roaming Act stipulates that rangeland conditions shall be carefully monitored to allow optimal viable herds of wild horses and burros in a non-prejudicial fashion. This clearly makes it illegal for the BLM to set the arbitrary, population-crippling Appropriate Management Levels (AML's) it has. Care must also be taken to preserve their free-roaming life style, by eliminating the blockage or piping of public water sources and the fencing and cross-fencing of the public lands.
Officials of the Bureau of Land Management, which now control wild horses and burros management on both BLM and USFS lands, currently are planning to allow what is equivalent to only one wild horse or burro to remain on the public lands per public lands livestock operator. This equates to approximately 17,000 wild horses and burros for 17,000 ranchers! To appreciate the inequity, each one of these ranchers may have 100's or even 1,000's of head of domestic livestock.
THE FORMULA FOR WIPING OUT THE HORSES & BURROS:
The remaining herds represent highly fragmented populations that in many cases cannot interchange genetically. Fences erected to rotate cattle and sheep from one "pasture" to another keeps herds away from healthy inter-breeding. Combine this with BLM's policy of removing younger animals, leaving predominately horses and burros older than 5 years of age and in many cases leaving only those older than 9 years of age, and it becomes clear that the BLM is setting our "national heritage species" (PL 92-195) up for inbreeding, winter kill, failure to reproduce, low vitality, population fragmentation and eventual extinction in the wild.
It seems ironic that our public servants charged under the law to protect wild horses and burros have in fact so perverted the law, as attested to in the General Accounting Office's Wild Horse Report to Congress of 1990 on the administration of the Act.
The public spends over $100 billion each year to simply enjoy wildlife including wild horses and burros and the wilderness ecosystems to which they are integral. They seek peace and quiet in a natural environment. They find these places and wild horses and burros who live there to be healing. And many people just want to know that wild horses and burros still enjoy their free life, whether they ever see them in the flesh or not.
ARE WILD HORSES AND BURROS SCAPEGOATS?:
Wild horse behavior patterns make them more ecologically harmonious when compared with livestock. Behavioral studies show that wild horses range widely throughout both steep, hilly terrain and lower, more level areas, while cattle concentrate on lower elevations where they camp on and destroy riparian meadow zones, laying them waste! Those who know wild horse habits, however, realize that a band will not camp on a riparian zone but will water in a quick and orderly fashion, then move on to highland grazing areas rarely frequented by cattle.
As a consequence and due to the judicious wide spread of grazing behavior of horses, range conditions in steep hilly areas which cattle do not frequent are generally much better than in lower areas. As is frequently the case, reducing horse populations in these areas has a negligible effect on the resource. As proof, after massive wild horse roundups, the herd areas show little or no improvement, since cattle numbers remain the same (or may increase). In spite of the foregoing, massive appropriations by the U.S. Congress for wild equid elimination has continued since the mid 1980's.
In their legal herd areas, wild horses and burros are the primary user, according to federal law. This should include at least 14% of BLM and additional U.S. Forest Service lands to total ca. 41 million acres, yet they have been eliminated from nearly half of these lands today. And it is especially important to note this, considering the relatively small percentage of public lands where wild horses have a legal right! Livestock grazing occurs on about 159 million acres, or about 64% of the 264 million acres under BLM control in the West. In spite of the gargantuan land size occupied by domestic livestock, the public lands produce less than 3% of the beef consumed in the United States. Clearly more important values here are at stake.