Although Difficult, Producers Can
Improve Fertility in Summer’s Heat
PLAIN CITY, Ohio, July 24, 2001 — While decreased production and weight gain
often are immediate side effects of summer heat, decreased reproductive
performance is another outcome that can cause long-term economic losses for
dairy producers. In addition to adopting management techniques that help
reduce heat stress, producers can improve reproductive efficiency by
implementing strategic estrus-synchronization programs, using artificial
insemination (A.I.) and breeding cows with highly fertile semen.
"At this time of year, providing cows with convenient access to shade and
ample supplies of cold water, and avoiding overcrowding are important keys
to managing heat stress," says Mel DeJarnette, reproductive specialist,
Select Sires. "Despite the best heat-management techniques, however, keeping
fertility high during the summer is still a challenge. Even though it can be
tempting to use a herd bull, top producers continue to use A.I. year-round,
recognizing that heat stress affects the fertility of bulls too."
Bull Fertility Suffers in Summer Heat, Too
Researchers at Virginia Tech, Blacksburg, Va., have conducted research to
better understand the effects of heat stress on semen production in bulls.
One study involved collecting semen at three-day intervals for a 10-week
period. After establishing baseline semen production, the researchers
mimicked heat stress by covering the scrotum of each bull with a sock made
of insulated batting material for 48 hours.
They found that semen quality began to decline approximately nine days after
the thermal insult, and that the maximum effect was not observed until 18
days after the insult. Semen quality then began to rebound, but normal
levels were not regained until 35 to 40 days after the sock had been
removed. Since the production of a sperm cell takes approximately 63 days
from start to finish, even a short-term heat stress can affect the semen
quality of herd bulls for as much as 1½ months.
"Extended periods of heat stress also can negatively affect semen quantity
and quality, and can decrease the bull’s libido," says DeJarnette. "The
bottom line is that you can’t depend on a herd bull to get cows bred during
the summer. That’s why more producers turn to highly fertile frozen semen
that has met stringent quality-control standards, including semen from sires
that have been designated as SUPERIOR SETTLERsTM."
Getting Cows Bred in Hot Temperatures
Research has shown that cows experiencing heat stress in the southeastern
United States have shorter and less-intense heats than cows in more
temperate environments. Heat-stressed cows are reluctant to spend energy
mounting and in other physical activity that would increase their body
temperature. So while cows typically continue to cycle normally (every 18 to
24 days), it is harder to catch them in heat.
Heat-stressed cows, however, do respond extremely well to prostaglandin
injections. That’s why estrus-synchronization programs can be implemented
effectively in conjunction with environment-management programs.
"Synchronizing groups of cows during hot weather can make heat detection
easier and more efficient," says DeJarnette. "This, along with intensive
management of heat detection and breeding, should help maximize pregnancy
rates."
What Can Producers Do?
Throughout North America dairy herds experience stress due to summer heat,
resulting in decreased production and reproduction performance. Although
producers cannot change the weather, they can adopt simple, inexpensive
management changes to help restore performance during the summer season.
Time-tested mechanical aids, such as fans and misters, continue to be
cost-effective options in the battle against heat. Since cows often reduce
their feed intake by as much as 25 percent during heat stress, increasing
the protein and energy content of feed while reducing fiber intake can help.
When it comes to managing reproduction, using estrus synchronization and
A.I. are always important tools.
"The best way to get more bang from your heat-detection buck is to use some
form of estrous synchronization," says DeJarnette. "In addition, fixed-time
A.I. options (e.g., Ovsynch) allow pregnancies to be achieved in the
absence of heat detection, enabling many producers to cruise through the
summer months with only modest declines in reproductive performance.
"It’s not too late to work with your veterinarian and other reproductive
specialists to develop a program that can help right now," he continues. "In
preparation for the summer of 2002, producers can reduce the number of cows
needing to be bred during the hottest months by strategically using a
synchronization program next spring."
Based in Plain City, Ohio, Select Sires Inc. is a federation of 10
farmer-owned and controlled cooperatives. It provides highly fertile semen
as well as excellence in service and programs to achieve its basic objective
of supplying livestock breeders with America’s best genetics at a reasonable
price.
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Click here for information on improving fertility in heat-stressed cows.
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Copyright 1996-2001 Select Sires Inc. Last updated 7-Aug-2001.
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