Page 315 - The Welfare of Cattle

292 the WeLfare of CattLe

COW LONGeVItY

Key components of a dairy farm’s economic health depend on more sales per cow and more
income over operating costs. Operating costs include the investment in raising a calf from birth to
first lactation at which time income from milk sales begins. That cost of caring for them to first
lactation, and the cost associated with the dry period of 40–60 days between lactations when cattle
are no longer being milked as they rest and recuperate before calving and starting their next lacta-
tion, must be paid for by milk sales. As those costs are repaid the operational cost for that animal
decreases and she becomes more profitable. In general, profitability peaks at third lactation when
the animal reaches their mature weight, achieves her maximum feed intake capacity, and has devel-
oped her maximum milk secreting tissues.
Cow longevity may be important to survivability of a dairy enterprise; however, economically
higher production levels make average herd life beyond 48 months less important when compared
to herds with lower production. A calculated optimum economic annualized removal rate of 25%
results in an average herd life of about 48 months (exiting in the 3rd lactation), and the study identi-
fied milk yield, milk price, feed costs, and replacement heifer prices as the most impactful variables
on removal rates. Lower removal rates of first and second lactation animals were seen as important
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economic goals because these animals are still paying for the debt incurred while they were raised
to the beginning of their first lactation. 7
Producers usually sit down and evaluate their monthly production test results, first to identify
those cows that are not producing at herd average thereby making them candidates for removal, and
then to compare those animals to others based on stage of lactation, lactation number, reproductive
status (non-pregnant cows are at higher risk of removal than pregnant cows), and somatic cell counts
(SCCs) in milk as a proxy for mastitis. Finally, they’ll likely look at other potential problems such as
lameness, conformation of feet, legs and udder, family/genetic potential, what fluctuations in herd
numbers are anticipated in the next month or so and the value if sold for beef rather than retained
for milk production. The decision to remove a cow from the herd comes down to whether another
animal replacing the candidate for exiting the herd will deliver more value to the herd both in the
short and long term.
Actuarial tables, sometimes called survival tables, are used in determining what we have to pay
for our life insurance by calculating how long we will live on average for our population. Social
security payments are also determined from actuarial tables. Both include data on race, occupa-
tion, geographical region, and other variables as they impact survival rates. They are also useful in
understanding turnover in dairy herds and these may include breed, production, lactation number,
and other variables that impact longevity. Figures 25.3, 25.4, and 25.5 show data taken from a study
of 13.8 million US dairy cattle by scientists at USDA. These survival tables relate to how long cattle
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stay in a herd and the term “survival” reflects exits from a herd for all reasons (including but not
limited to on-farm death). In Figure 25.3, the authors show survival rates (how long they remained
in the herd) for the two most popular breeds of dairy cattle in the US across five consecutive years
after their first calving. The slope of the line indicates a pretty constant rate of exits up to 4 years
after first calving and more rapid removals thereafter. There are some impacts of breed on longevity.
In Figure 25.4, the same authors present the mean months an individual cow stayed in the
herd, reported by the year of first calving, excluding any cows at or beyond their 9th lactation.
Breed differences are evident. Average longevity declines from about 1981 until it starts increasing
for unknown reasons in 1990. Holsteins “lost” ~4 months of longevity in this 15 year period, and
Jersey’s and Guernsey’s each lost ~2 months.
Figure 25.5 shows the percentage of three breeds of cows remaining in the herd by parity.
Taking Holsteins as an example, about 25% of those in the herd at first calving are gone before the
end of their second lactation, and another 25% exit by the end of their third lactation. Exit rates then