American Bison - Buffalo Field Campaign

4. Health and disease
All attempts should be made to prevent the spread of disease
between bison herds. Even if the recipient and donor herds host
the same disease, transfers of bison should be discouraged
since disease strain variants between herds can lead to
differences in disease progression or effects. Potential donor
herds should be thoroughly tested (see Chapter 5 and section
above) to evaluate the presence of pathogens.
Once the above factors have been evaluated, there are various
other features that may influence the demographic and genetic
effects of the transfer, including the number, age, and sex of
the imported bison as well as frequency (single or multiple
introductions) and duration of the transfers (permanent vs.
transient transfers, e.g., for short-term breeding). Each situation
will differ and a comprehensive review is not possible here given
the large number of potential management scenarios. However,
the general guidelines in Table 9.3 should be considered.
Table 9.3 Risk factors for disease.
Disease Risk Factors Disease Examples
(not all-inclusive)
History of pathogen in the
region
Proximity to potentially
infected populations
(wildlife or livestock)
Weather patterns and
environmental suitability
Presence/abundance of
mechanical or biological
vector(s)
Population density
(increased infectious
contacts)
Anthrax, parasites
MCF, Bovine tuberculosis,
brucellosis, Johne’s disease,
bovine viral diarrhoea, foreign
animal diseases (e.g., Foot-and-
Mouth Disease)
Anthrax, parasites
Anaplasmosis, bluetongue, pink
eye
Most infectious diseases (e.g.,
brucellosis, tuberculosis)
Season Diseases with unique
transmission patterns (e.g.,
brucellosis, bluetongue)
Nutritional and other
environmental stress
Geographic location/
Climate
5. Number
Infectious diseases which
capitalise on depressed
immunity (e.g., respiratory
viruses)
Hardy pathogens capable of
surviving climate extremes
The number of imported bison should be based on prior
modelling estimates when possible, and should reflect the size
of the population so that improvements in heterozygosity and
genetic diversity are maximized with a minimum dilution of the
native bison germplasm.
6. Sex
Importing a few males into a herd can have a large and rapid
genetic and demographic impact. The same overall effects can
be obtained when importing females, though the process will
be somewhat slower. In some cases, it may also be worthwhile
to consider any known genetic uniqueness of the mitochondrial
genome and Y chromosome. For instance, prior to importing
bison into the Texas State bison herd, it was noted that this herd
contained a unique bison mitochondrial haplotype not known
to occur in other bison herds (Ward et al 1999; Ward 2000).
Therefore, importing males into this herd was favored over
importing females, in part to prevent dilution of the unique native
bison mitochondrial haplotype (Halbert et al. 2005a).
7. Age
Clearly the most rapid infusion of germplasm and improvement
in herd viability will be obtained by importing breeding-age
animals. In some cases, it may also be desirable to choose bison
that have already produced offspring to avoid potential issues
of sterility or offspring abnormalities. Even given the most well
thought-out plans, however, genetic incompatibilities between
native and imported bison may still influence the effectiveness of
the imported bison in contributing to the calf crop.
8. Quarantine
A quarantine of newly imported bison should be considered prior
to their release, especially when the recipient herd is at a high
risk of extinction. Isolating the newly imported bison for some
time will allow for an easier adjustment of the imported bison
to their new environment and early detection and treatment/
removal of latent diseases.
9. Mating regime
Should the imported bison have exclusive mating privileges
for one or more years or should they be included with all
other potential breeders to compete for breeding rights? An
“exclusive” mating regimen allows for larger potential genetic
and demographic impacts. However, a “competitive” mating
regimen permits native bison to continue to contribute to the
gene pool each year and provides some protection in case of
genetic incompatibility between the donor and recipient herds.
9.2.6 Recovering small or threatened herds
Small populations (N e less than 50, or a census size of fewer
than about 150 animals), or larger populations which have
undergone a recent and significant decrease in population
size, are especially vulnerable to a loss of genetic variation,
decreased fitness, and, ultimately, extinction (Gilpin and Soulé
1986). Persistently small populations are additionally susceptible
to inbreeding, which can lead to an overall loss of heterozygosity
and increase in rare, and often detrimental, genetic traits.
American Bison: Status Survey and Conservation Guidelines 2010 91