Cows, Carrots And Heat Stress
GEORGE F.W. HAENLEIN
Extension Dairy Specialist
University of Delaware
NEWARK, Del. There’s an
old saying: “What’s good for
horses is good for cows, and may
be even humans.”
That is one reason oats is a
popular feed, although for cows,
the price doesn’t fit into the least
cost ration formulation.
Carrots is another example.
Horses love them and a regular
feeding of carrots makes their
haircoat glossy. But not too many
dairy farmers feed carrots to their
cows, not even to their prize cows.
Cost and labor in handling small
carrots is one reason.
In this country we do not feed
cows the bigger root vegetables,
such as rutabagas, mangles or
cowbeets, as farmers still do in
Europe. Instead, we have turned to
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the chemical-pharmaceutical in
dustry for cheaper extracts with
(we hope)— the same nutritional
benefits. Instead of feeding car
rots, we add a carotene supple
ment to the feed ration. However,
there are several different caro
tenes and, we hope, the beta-caro
tene is the right one.
Actually, carotenes have some
unique metabolic properties be
yond the empirical benefit of glos
sy haircoats. These properties are
called antioxidant In research
with embryos of cows and mice, it
has been found that antioxidants
protect them against deleterious
effects from the elevated tempera
tures that are experienced on hot
summer days. In new research at
the University of Florida (appro
priately), this reputation of anti
oxidants was tested to possibly re
duce bovine embryo losses.
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Soon we may have Florida-type
heat here too. so this research of
fers interesting possibilities for
application. Heat stress generally
reduces conception or pregnancy
rates in dairy cows. It has been de
termined that in Florida the aver
age pregnancy rates of 45 percent
in winter are drastically reduced to
less than 10 percent during the
hottest summer months. Also, heat
stress reduces the expression and
length of estrus behavior, thus
fewer cows are detected in estrus.
Consequently, fewer cows are
bred by artificial insemination
than should be. resulting in fewer
pregnancies, longer calving inter
vals and longer lactations with
less milk production per day.
To alleviate the bad effects of
heat stress, Florida has pioneered
ways to cool cows, such as erect
ing cloth covers to shade cows in
feeding and holding areas and,
even more effective, a combina
tion of overhead sprinklers and
fans for evaporative cooling. The
University of Delaware dairy herd
has benefited from these cooling
means also, even though our cows
are not subjected to that much
Florida-like heat A number of
farm magazines have written on
this topic at this itme, because
these methods pay off outside of
Florida, too.
However, even with the best
cooling systems, studies compar
ing calving intervals for winter vs.
summer breeding in Florida have
shown that the intervals are differ
ent and still too long for summer
breeding.
A new strategy being tested is
timed artificial breeding, or timed
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A.I. This involves the use of sex
hormone injections into cows to
induce ovulation at a precise, pre
dictable time a few days later.
Thus, there is no more need to
worry about observing estrus in
cows or missing any.
The precise estrus time after
hormone injections means that a
greater efficiency in inseminating
cows is achievable. At least this is
the hypothesis of the new Florida
research. The study was con
ducted at two commercial dairy
farms, one in southern and one in
northern Florida over a 12-month
period with 700 Holstein cows.
They had the benefit of overhead
sprinkler cooling. Added to their
complete ration were 400 milli
grams beta-carotene per day for
the experimental cows, at least IS
days before breeding. These cows
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