Comparing the lifespan of Bison to cattle is much the same as comparing a Donkey (30-50years)to a Horse (25-30 years).
I was reading this article which I think is highly informative.
Beef Cow Longevity
by Jane Parish – Extension Beef Cattle Specialist, Mississippi State University
The focus of cow longevity discussions is often on dairy cattle. However, to a beef cowcalf
operator, cow longevity is a major factor affecting costs and thereby profitability.
Two definitions for longevity are “the length or duration of life” and “length of service,
tenure, etc.; seniority”. Considering that cows must not just survive many years but also
must be productive in later years to be exempt from culling, the latter definition is most
relevant view of cow longevity to cattle operations.
Productive longevity is the age at which a cow dies or is culled from the herd due to her
presumed inability to continue as a productive brood cow and dam. Unlike cows that
die, cows that are culled have a salvage value. This salvage value increases with
improved cow condition and health. Therefore, it is important to recognize signs that
productive longevity is nearing an end and to market cows in a timely manner before
salvage losses occur. The old saying, “just one more calf” illustrates that some
producers push their luck when trying to get as many productive years out of a beef
female as possible. Beef Quality Assurance guidelines promote timely marketing of
market cows due to their role as an important food source and also from an animal
welfare standpoint.
Greater longevity has its benefits. It allows producers to be retain fewer replacement
heifers and lowers overall replacement costs. When fewer replacement heifers are
needed, the operation can be more selective when deciding which heifers to keep.
Herds containing a larger proportion of mature cows usually have a higher percentage
of calf crop weaned, wean heavier calves, and have lower total energy requirements.
Cow maintenance costs are also spread out over more calves. Increased longevity can
both reduce production costs and increase annual pounds of marketable calf per cow.
For purebred cattle breeders, increased longevity allows greater selection intensity for
other important traits. Disadvantages of greater longevity are that it increases
generation interval and thus potentially reduces genetic gain per year by less
aggressively replacing “old” genetics with improved “new” genetics.
It is not uncommon for breeding cattle to live well into their teens. Some producers even
brag about having cows in their herds that are “old enough to vote”. However, despite
some cows reaching this advanced age and remaining in production, many more cows
typically leave the herd at much younger ages. One large Florida ranch dataset showed
consistent rebreeding performance in its cows through about 8 years of age.
Reproductive performance consistently began to decline at 10 years of age and
dropped even more steeply at 12 years of age. Some research suggests that maximum
longevity for optimum economic returns is within the range of 8 to 11 years for
commercial cow-calf operations.
Longevity is a convenience trait that is highly variable. Yet it only takes small changes in
longevity to greatly impact herd profitability. Many traits influence cow longevity
including age at puberty, direct and maternal calving ease, milk production, mature size,
ability to store body fat (fleshing ability), ability to endure weather extremes, udder
soundness, skeletal soundness, disposition, freedom from genetic defects, and many
more characteristics. Physical soundness limits the productive life of a cow as she ages.
For example, tooth wear and loss occurs over time and affects a cow’s ability to harvest
forage, consume feed, and maintain body condition. Fertility, maternal ability, health,
and survival of a cow and her calves are the primarily determinants of longevity.
Cows are culled from herds for many reasons. Age or bad teeth (57.8% of operations)
was the most commonly declared reason for marketing cows followed by pregnancy
status (25.6% of operations) as reported in the National Animal Health Monitoring
System’s Beef ’97 study. The percentages of operations culling cows for other reasons
were 14.1% for economic reasons such as drought, herd reduction, or market
conditions; 11.7% for poor producing calves; 8.2% for other reproductive problems;
6.4% for physical soundness; 6.4% for temperament; 5.8% for udder problems; 4.1% for
bad eyes; 1.0% for respiratory problems; and 0.3% for digestive problems. Larger
operations, in terms of herd size, were less likely to market cows for economic reasons
than smaller operations. Calving difficulty, advanced age at first calving, and producing
less than one calf per year increase the likelihood of culling.
Valuable data in evaluating cow longevity include records of how long each cow stays in
a herd and the reason why each cow leaves a herd. Whole herd reporting (including
herd inventory reporting) and reporting reproductive data is important to breed
associations tracking longevity for use in genetic predictions. Genetic predictors for
longevity include EPDs for stayability. Stayability indicates differences in the percentage
of daughters remaining in the herd at 6 years of age. Six years is used because a study
showed that cows typically did not repay their development cost until their fifth calf (born
to 6-year old cows if calving annually starting at 2 years of age). Genetic lines that
produce a greater percentage of females producing to 6 years of age are more likely to
also be productive at much older ages and produce more lifetime revenue. Relatively
effective selection for stayability is possible due to moderate heritability of this trait.
Breed differences exist in longevity, so replacement rates differ by breed. In one study,
cows were culled for different reasons, and breed influenced culling reason. Another
study showed that crossbreeding to Brahman increases longevity of cows for beef
producers in the South more so than crossbreeding to Angus, Hereford, or dairy breeds.
Within breeds, a key factor in longevity is matching cow mature size and milking level to
the production environment. When production resources cannot keep up with the
demands of a particular cow size or milking level, rate of culling is likely to increase.
Longevity of crossbred cows is generally greater than that of purebred cows. Crossbred
cows typically live longer and are more productive than their purebred counterparts.
Maternal heterosis (hybrid vigor) increases longevity by more than one year. Because of
the low heritability of cow longevity and lack of indicators of longevity expressed early in
life, implementing crossbreeding systems to take advantage of maternal heterosis
becomes even more important to improving longevity of the breeding herd.
To improve cow longevity, keep good reproductive and herd removal records, take
advantage of the maternal heterosis of crossbred cows, and use stayability EPDs when
available. Decide on the best balance of retaining females in the herd to advanced ages
and culling earlier to increase rate of genetic improvement and protect cow salvage
value.
