Problems and Solutions for Maintaining Pregnancy Rates in Summer Heat
Herd Bulls Can't Cure Summer Heat Problems 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 can affect
embryonic mortality. In the short term, high ambient temperatures
can 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 (CL). The CL and the progesterone it
produces are essential for maintaining pregnancy. Thus, any stress
(heat or otherwise) applied to an animal can influence the quality
of eggs and/or CLs 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 Bulls
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 (see figure 1).
What does this mean for a herd bull running with the cows during heat
stress? Research conducted at Virginia Tech1 found that even a mild heat
stress for a short period of time (48 hours) can affect the quality of
semen the herd bull produces for as long as 1½ months. 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: you can’t depend on the herd bull to get cows bred
during the summer months.
Selecting Highly Fertile A.I. Sires
Using semen from A.I. bulls that have been screened for semen quality
gives a reproductive advantage that a herd bull can’t - especially in
summer heat. When using A.I. bulls that have been screened for semen
quality, fertility will not differ more than 10 to 15 percent from the
highest- to the lowest-fertility individuals. Greater than 90 percent
of active-A.I. sires are within 3 percent of breed average for fertility.
To keep sire fertility in perspective, it’s important to recognize that
environmental and management factors cause conception rates of individual
herds to range from less than 20 percent to as high as 60 percent. A herd
that has been using average-fertility A.I. bulls can use fertility in sire
selection to move 2 or 3 percentage points in the right direction. However,
no bull can change a 20 percent fertility herd to a 60 percent fertility herd.
For decades Select Sires has published information about the fertilizing
capacity of semen from its bulls. Just as there are differences in
genetic-transmitting ability between bulls, so are there differences in
the fertilizing capacity of spermatozoa from different bulls. Select Sires’
SUPERIOR SETTLER™ listing recognizes those bulls that have achieved a
superior fertility index that ranks them among the elite fertility bulls
in the Select Sires lineup.
Why is Fertility of A.I. Sires More Reliable?
The standards that each and every bull must meet illustrate why SUPERIOR
SETTLERS are truly elite fertility bulls among a very highly selected group
of all active-A.I. sires.
First, each bull housed at Select Sires has been given the very best housing (including air conditioning)
and health care available. Few humans have had as many complete physical
examinations as a Select sire.
Semen is collected, processed, packaged and frozen using the latest scientific
technology. Samples are thawed and reevaluated to determine whether the proper
numbers of motile spermatozoa are present for optimum fertility. Samples
from each bull also are evaluated routinely to ensure normal sperm morphology.
The semen is released for sale only if Select’s high quality standards are met.
Next, data from cows inseminated by the Select Sires technician force are sent
to Select Sires and used to compute a non-return rate. The non-return rate is
the percentage of cows reported for first-service insemination that were not
reported for a second-service insemination within a defined period of time.
The SUPERIOR SETTLER designation is based on six months of historical
semen-quality data (including post-thaw motility, incubated motility, incubated
intact acrosomes and spermatozoa morphology) combined with current non-return
data in a model to provide an index. Only bulls that have the highest semen
quality and the highest non-return rates to back up laboratory analysis are
given the elite status of SUPERIOR SETTLER.
Because great emphasis is placed on semen quality traits during the previous
six-month period, SUPERIOR SETTLERS can be considered a "predictive" estimate
of what fertility will be in the next few months.
If you have a concern about fertility, Select Sires offers the most
well-trained field staff and a team of reproductive specialists that
can be a tremendous resource to you.
1Data on file
August 2007
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While the greatest variables affecting pregnancy rates are
the accuracy of heat detection, inseminator technique and
other management factors, looking at fertility values of
individual sires can help. For years Select Sires has placed
the SUPERIOR SETTLER™ designation on sires that meet stringent
requirements for semen fertility. Trust Select Sires as your
source of highly fertile semen and balanced genetics - because
you want more than just a pregnancy.
"Select" sires designated as SUPERIOR SETTLERS based
on a combination of their current semen quality and
historic non-return data.
SUPERIOR SETTLER MILK %REL TYPE %REL
7HO5710 DANE +889 99 +1.18 99
7HO6512 CLASSIC +689 91 +.87 83
7HO6682 MARMAX +2,104 99 +1.28 97
7HO6695 LC +1,031 91 +1.12 85
7HO6745 ONYX -344 96 +1.52 92
7HO6838 MATCHES +1,719 88 +1.67 84
7HO7037 MILES +23 88 +2.30 86
7HO7193 DESIGN +2,189 97 +2.16 94
7HO7218 LYLE +1,192 91 +2.01 87
7HO7285 HHF +529 91 +2.19 87
7HO7452 FRITZ +1,568 90 +2.06 86
7HO7455 GRANGER +941 88 +2.23 85
7HO7463 PONTIAC +873 90 +2.41 86
7HO7466 MOSCOW +1,589 97 +2.19 94
7HO7536 COLDSPRING +682 89 +2.23 87
7HO7544 FRASIER +1,197 87 +2.03 86
7HO7560 BLITZ JINTX +2,525 96 +1.62 91
7HO7650 JACKSON +850 97 +2.64 92
7HO7785 REAGAN +1,128 90 +2.39 87
7JE590 ACTION +475 92 +2.3 82
7JE620 MAXIMUS -18 96 +1.0 93
7JE681 TELMARK +449 86 +0.6 75
7JE714 MATINEE +719 78 -0.1 79
* = New Active Sire
Based on advanced laboratory semen quality evaluation
techniques, these sires have the best probabilities
of becoming SUPERIOR SETTLERS in the future.
SUPERIOR SETTLER MILK %REL TYPE %REL
7HO7514 RE DESIGN +478 86 +2.65 72
7HO7653 ROSS * -137 83 +3.27 68
7HO7712 SOCRATES +1,462 88 +2.21 86
7HO7725 ALLOCATE * +1,457 88 +0.62 86
7HO7737 MENDEV * +1,438 85 +1.97 83
7HO7762 FLINT +1,390 87 +2.19 86
7HO7838 GLEN +882 88 +2.77 85
7HO7895 SEGER +1,594 87 +1.67 86
7JE679 RAY +468 85 +1.5 74
7JE712 AWARD +29 92 +1.3 88
7JE731 LOTT +1,374 85 +0.8 75
* = New Active Sire
™SUPERIOR SETTLER is a trademark of Select Sires Inc.
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