Get Ready, Summer's Coming
By Mel DeJarnette, reproductive specialist
We’ve all heard the phrase "an ounce of prevention is worth a pound
of cure". But how many have ever stopped to apply this concept to
summer breeding problems?
Each year, stress associated with high heat and humidity wreaks
havoc on reproductive performance of dairy herds nationwide.
Although there are numerous "cures" we can adopt to minimize stress
and improve breeding efficiency of animals during the summer months
(i.e., shade, fans, sprinklers, etc), the best alternative is to
"prevent" animals from needing to be inseminated during the summer.
No matter what we do, all herds will have some cows that need
inseminating during the summer. But, if we can adopt management
procedures to get a higher percentage of the herd pregnant during
the spring, there will be fewer headaches to deal with in the summer.
Now is the time to get started.
Heat Detection
Spring is a very hectic time on most dairies. Cows conceiving last
spring need breeding again and crops need planting. All too often
the latter takes precedence. Don’t let the value of good heat
detection slip through the cracks while the corn planters are in
the field. This may take some rescheduling of labor or possibly
adding some part time help to cover all the bases.
Since time is usually a critical limiting factor during the spring,
we want to make sure that time spent for heat detection is used
efficiently. Cows are not particularly interested in displaying
mounting activity when they are distracted by other activities such
as feeding or milking. Schedule heat detection periods to coincide
with your cows’ "leisure" time.
Estrous Synchronization
The best way to get more bang from your heat detection buck is to
use some form of estrous synchronization. By stimulating groups of
cows to come into heat at the same time, you focus your limited labor
more effectively. At the same time, mounting activity increases several
fold with multiple cows in heat. A prostaglandin based breeding program
such as that described in the March-April issue of Selections is just
what the doctor ordered.
Dr. Herd Bull Can't Cure Summer Heat Problems Either
For two reasons:
- Summer breeding problems are usually a reflection of cow fertility, and
- Bulls get heat stressed too!
Cow Fertility
There are two possible mechanisms by which heat stress may affect
embryonic mortality. In the short term, high ambient temperatures
may negatively influence the uterine environment and its ability to
maintain development of a viable embryo.
Secondly, the physiological process necessary to grow and "ripen" a
follicle and egg requires about 60 days from start to finish. Once
ovulation occurs, the cells that previously lined the follicle walls
grow to form the corpus luteum (C.L.). The C.L. and the progesterone
it produces are essential to maintenance of pregnancy. Thus, any stress,
heat or otherwise, applied to an animal may influence the quality of eggs
and/or C.L.s produced for the next two months. This partially explains
why cows typically don’t fully recover from heat stress until late October
to sometime in November.
Heat Stress in Bull
Researchers at Virginia Tech evaluated the effects of heat stress on semen
production in bulls. Bulls were collected at three day intervals for a
period of approximately ten weeks. The first two weeks of the project were
used to establish a "baseline" of normal semen production for each bull, respectively.
To mimic the effects of heat stress, the scrotum of each bull was covered
for 48 hours with a sock make of insulated batting material. The results
are shown in figure 1.
Approximately nine days after the thermal insult, semen quality began to
decline. The maximum effect was not observed until about 18 days after the
insult. Semen quality then began to rebound. However, normal levels were
not regained until approximately 35-40 days after the "sock" had been removed.
Like making eggs, producing a sperm cell takes approximately 63 days from
start to finish. Thus, when spermatogenesis is disrupted (as with heat stress),
it takes time for all of the affected cells to pass through the system.
What does this mean for your herd bull running with the cows during heat
stress? From this experiment, we can safely say that even a mild heat stress
for a short period of time (48 hours) may affect the quality of semen the
herd bull produces for as much as a month and a half. Extended periods
(weeks) of heat stress may:
- have negative effects on the quantity of sperm a bull produces.
- extend the amount of time required for recovery of normal levels
of semen production and
- reduce the bull’s libido or sex drive.
The bottom line is: we can’t depend on the herd bull to get cows bred
during the summer months.
Like it or not, summer’s just around the bend. Now is the time to prepare.
Use your spring wisely to get as many cows pregnant as possible before
the summer breeding slump arrives.
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