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Herd reproduction is
considered to be the output or production trait with the greatest economic
impact on commercial cow calf profitability. Likewise feed is the input cost
of greatest significance in differentiating high or low profit operations.
The heritability of reproductive traits is considered low. Most of the
differences we see in herd reproductive rates are attributable to
non-genetic environmental factors, primarily nutrition. Herd reproduction
and nutrition, the two biggest influences on profitability are closely
connected and need to be evaluated together. Often times, small investments
can have a high rate of return. However further investments in feed to get
maximum reproduction aren’t likely to maximize profit.
Herd economics are
affected through reproduction in both the number of calves produced and the
culling and replacement rate. As pregnancy rates increase and calf losses
are minimized, cowherd expenses are spread over more marketed calves and the
cost of production is lowered. With annual cow costs of around $400 per cow,
each additional 1% weaned calf per cow maintained lowers the cost per calf
by around $5. Open and late bred cows are typically sold and make up the
largest portion of culled cows. Income from culled cows will typically
offset only 50 to 60% of the expense of developing or buying replacements.
At a differential of $500 between culls and replacements, every additional
1% culled increases ownership cost per cow by about $5 per cow. Increasing
reproductive success produces more calves, prolongs cow’s life in herd, and
reduces the number of replacements needed.
The development of heifers and management of young cows set the stage for
overall herd reproduction. In general terms, heifers should be grown out
from weaning to breeding at not more than around two pounds per day to
minimize fat deposition targeting a body weight at breeding of at least 60%
of expected mature size. By achieving such growth we expect heifers to reach
puberty and be ready to breed at 13 to 14 months of age. Adding an ionophore
to heifer development rations will increase growth and hasten puberty.
There are several advantages related to synchronizing estrus of heifers to
increase percentage exhibiting heat at the start of breeding season. It
helps insure a “tight” calving season which reduces labor at calving but
also contributes to shorten subsequent calving. Synchronized heifers also
create an opportunity to use A.I. breeding for greater accuracy in selecting
superior calving ease sires. From breeding on to calving heifers must be
grown out to about 80-85% of their mature weight by time of calving and be
in good flesh. By doing so, calving problems will be minimized and the
probability higher for the first calf heifer to return to estrus in time to
stay on schedule and remain in the herd.
Since first calf heifers are still growing and partitioning nutrients
between growth, milk, and reproduction they often have difficulty
rebreeding. The key to breed back and staying on schedule is nutrition. The
heifer’s body condition should be monitored during the months prior to
calving. It is often necessary to sort from mature cows to provide
supplemental or higher quality feed. This is often the case for 2nd
and 3rd calf cows that may have been pulled down in condition
during lactation.
Using the body condition scoring system to assess the nutritional status is
helpful. BCS at calving is a good predictor of subsequent pregnancy rate.
The target for heifers is 6+ while for mature cows a 5 is adequate. Cows
that calve at a BCS of 4 will typically have a 25% lower bred back in a 60
day breeding season than cows at desired condition. By supplemental feeding
or flushing thin cows after calving this difference may be improved to 5-10%
difference, but is still likely to be less. Pregnancy rates of late calving
cows can be enhanced with some estrus synchronizing protocols. “Priming” the
reproductive system with progesterone as through using a CIDR can help
induce non-cycling cows to exhibit estrus and breed.
Limiting the breeding season along with management procedures such as
vaccination and pregnancy testing can help identify fertility problems and
assist in culling and replacement decisions. Placing some limits on the
breeding or calving season prevents perpetuating poor reproductive
performance and greatly aids in producing a more uniform, manageable, and
marketable calf crop. It also allows for defined analysis and benchmarking
of herd growth and reproductive performance.
From the commercial producers point of view there is greatest biological
efficiency when the breeding and calving season is matched with forage
production. The peak nutrition time for cows will be 45 to 60 days into
lactation, which is just prior to breeding. Pasture type, grass species, and
grazing management can affect forage curves which peak in June for many cool
season grasses in the northern plains. From an economic perspective many
seed stock breeders calve a month or two earlier than optimum to meet the
needs of customers for older bigger bulls. As well a number of commercial
producers calve earlier targeting heavier calves capable of capturing valve
for finishing at seasonal market highs. Some premium is needed to offset
additional feed inputs to achieve high herd breeding when calving out of
season.
Matching
nutritional demand to forage quality and availability is not only influenced
by scheduling the cow herd, but also through genetic selection. Herd
reproduction is greatest when genetics for size, milk, and productivity are
matched to the available forage resources which generally favor moderation
in biological type. Furthermore, planned use of crossbreeding to utilize
crossbred cows of adapted breeds of appropriate productivity, can greatly
impact reproductive traits and longevity in the herd. The overall benefit
equates an additional calf per cow.
One of the more difficult challenges is how to match the cow herd to the
forage resource and still produce calves with the greatest feedlot and
carcass value. New heifer pregnancy, cow maintenance, and carcass EPD’s are
tools to help manage this compromise. Further advancements in DNA technology
and sexed semen will make efficiencies of terminal crossing superior product
lines on best fit material lines more feasible.
While concerning ourselves with cow fertility, herd nutrition, and feed
costs; we can’t overlook the bull. Lots of things can reduce a bull’s
ability to breed and settle cows, and the impact of an unsound or infertile
bull is huge. Good selection, nutrition, conditioning, and health are
critical. A breeding soundness exam on each bull each season will help
determine bull fertility and fitness for use. Testing bulls not only helps
insure against a breeding disaster, but in general pregnancy rates, and
first service conceptions are higher in herds using bulls that pass a
breeding exam compared to bulls of unknown classifications.
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