Beef Reproduction I, II & III
Supplement for CEV #205 - 207
Goal:
The student focuses on the efficiency demands of the industry and how
these can be met through selective reproduction.
Objectives:
1. to select the appropriate breeding stock
2. to understand the male and female reproductive anatomy
3. to appreciate the importance of the male and female germ cells
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Beef Reproduction
Supplement for CEV #205-207
Introduction
In order to meet the goal of the beef industry--providing meat at a reasonable
cost--today’s cattle producers have to produce calves as efficiently as possible.
The meat packer wants slaughter beef that grades “choice,” but it must have a
minimum of external fat. Feeders want calves that will gain the most amount of
weight on the least amount of feed. Meeting the needs of these markets is
challenging, and the producer’s greatest tools are proper management practices
and use of genetics to select production cattle that can meet those market needs.
To have a marketable product, cattle producers must first be able to select
breeding stock that will produce the highest quality offspring. Once the breeding
stock has been selected, the producer must be able to produce these offspring
as efficiently as possible. One key to efficient production is the reproductive
efficiency of the herd. Despite how well the offspring perform, if the cows do not
produce enough calves to pay for themselves, reproductive efficiency is lost.
Section I: Beef Reproduction I
Selecting Breeding Stock
The bull and cow herd are the foundation for calf production, which in turn either
become replacement cattle, are sold as a cash crop, or go to the feedlot for
fattening as slaughter cattle. Producers should attempt to purchase cattle that
are well known to produce the right results. For example, breeds such as
Charolais, Limousin, and Simmental are known for producing lean meat, and
breeds that are well known for their meat tenderness include Shorthorn, Angus,
and Hereford. In order to select the best cattle to raise, the producer must take
into account the environment and select cattle which will thrive in the temperature
and climate for the region.
Selecting Suitable Cattle
The type of environment where the cattle will be raised should be considered
when selecting breed types. If the cattle are not suited to their particular
environment, efficiency will be reduced.
Warm-weather Cattle
Bos indicus cattle are particularly suited to hot, tropical climates of the southeast
and gulf coast as well as the arid desert climates of the southwestern United
States. Purebred Bos Indicus (also called Zebu cattle and often improperly called
“Brahman” cattle) that are being raised in the United States include Nellore, Gir,
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Guzerat, Indu-Brazil, Watusi, and the American Brahman. These cattle are
extremely hardy and can survive and reproduce on the sparse vegetation of arid
climates, and can withstand the insects and humidity of southeastern and gulf
coast regions.
The offspring of Bos Indicus and Bos Taurus crossed cattle are well-suited for
beef production, for the offspring retain the excellent heat/humidity and
insect/parasite resistance of the Bos indicus parent and the faster meatproducing ability of the Bos taurus parent.
Cool-weather Cattle
Continental and British, or Bos taurus breeds, are more adapted to the mid and
northern United states where the winters are cold and the summers are mild.
These cattle are able to gain weight in feedlot situations without suffering from
cold temperatures.
These cattle are also often crossed to produce an offspring more suited to their
particular environment. If crossed with Bos indicus, the cattle gain thriftiness and
insect/disease resistance from their Zebu parent. They are often crossed with
other Bos taurus types to blend the best qualities of both breeds.
Cross Breeds and Composites
Often, the best cattle for a particular area may be crossbred animals that are part
Bos indicus and part Bos taurus. These animals are able to withstand the rigors
of climates in many parts of the country and efficiently combine the disease
resistance and thriftiness of Brahman-influenced breeds with the muscling and
high quality meat production of British and Continental breeds.
Cross breeding often results in a hybrid vigor called heterosis, which is the
amount of improvement in the performance of the crossbred offspring over the
average of the purebred parents.
Some popular Bos Indicus and Bos Taurus crosses and composites produced in
the United States include:
Braunbray (Braunvieh x Brahman)
Gelbray (Gelbvieh x Brahman)
Bralers (Brahman x Salers)
Simbrah (Simmental x Brahman)
Brangus (Brahman x Angus)
Beefmaster (Hereford x Shorthorn x Brahman)
Brah-Maine (Brahman x Maine-Anjou)
Greyman (Murray Grey x Brahman)
Brahmousin (Brahman x Limousin)
Sabre (Sussex x Brahman)
Braford (Brahman x Hereford)
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Charbray (Charolais x Brahman/Zebu)
Santa Gertrudis (Shorthorn x Zebu)
American Breed (Hereford x Milking Shorthorn x Bison x Charolais x Brahman)
Barzona (Hereford x Africander x Santa Gertrudis x Angus x Indu-Brazil)
Some popular Bos Taurus crosses and composites in the United States include:
Salorn (Salers x Texas Longhorn)
Black Baldie (Hereford x Angus)
Murray Grey (a specific Shorthorn cow x Angus)
Senepol (British Red Poll x N’Dama)
Chiangus (Chianina x Angus)
Chiford (Chianina x Hereford)
Beefalo (Bos bison and Bos taurus cross)
Bulls
Whether you are cross breeding or pure breeding, the bull is the most important
individual in the herd. The bull is the source of half the genetics of every calf in
the herd. Therefore, it is critical to select the proper sire to complement your cow
herd. Areas you should check when selecting bulls are performance records,
structural soundness, muscling, temperament, and reproductive soundness. If
these areas are adequate, then the bull should undergo a breeding soundness
check from your veterinarian.
Performance Records
An important selection tool is the Sire Summary that is published for most breeds.
The most important vital statistic in the Summary is the Expected Progeny
Difference (EPD), which predicts the performance of a bull's offspring when
compared to the average of the offspring of other bulls in that breed. EPDs are
only valid within the breed; they are not used to compare bulls of different breeds.
EPDs are calculated for production traits such as growth, maternal ability, calving
ease and, in some breeds, carcass traits.
Reading EPDs
Keep in mind that the EPD number is expressed as units of the trait. For
example, weaning weight EPDs are expressed in pounds. The number reflects
how the offspring perform relative to the average of the breed. The breed average
is always set at zero, so a weaning weight EPD of +5 means the calf is predicted
to wean 5 pounds above the average of the breed. The average often is derived
from a base year for the breed. As improvements are made through selection, the
breed average for the current year may increase, but the base year average
remains the same.
EPDs are followed by a value that ranges from 0 to 1. This value is the accuracy
of the EPD, which tells the reader how certain he or she can be that the offspring
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will perform as predicted. When more offspring are added to a bull's records, the
accuracy increases accordingly. The EPD is calculated from the performance
records of the bull's offspring, his performance, and the performance records of
parents, grandparents, full siblings and half siblings. Maternal traits are
determined from the maternal performances of the mother, grandmother,
daughters, sisters and half sisters. These traits are often determined from the
weaning weights of these female offspring. For example, records for a bull's
maternal ability may actually be the weaning weights of his daughter's offspring.
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Structural Soundness
A bull that is not structurally sound will not have the stamina to travel the pasture
and breed all the cows in the herd, or will not be able to support himself when
mounting the cows. Either problem will result in cows not getting pregnant and
the production efficiency of the herd going down. Check the physical features of
the bull. He should have large feet with toes facing forward, free of cracks, curls,
and infection. Pasterns should be strong and straight, knees should flex easily,
hocks should have a good angle to allow him to walk well and support his weight
while breeding.
Muscling
Another factor affecting fertility and structure is the degree of muscling in the
cattle. The main objective of the beef industry is to produce a healthy, appetizing,
and saleable product: BEEF. The amount of muscling in an animal determines the
percentage of boneless, closely trimmed retail cuts the carcass will yield. This is
important to the efficiency of beef production. However, extremes should be
avoided. Extremely heavily muscled or double muscled cattle may have structural
problems which reduce fertility. On the other hand, light-muscled bulls are often
not hardy enough to complete a breeding season without losing some fertility.
Temperament
In selecting a bull for your herd, select those with a good temperament. Such
bulls will eliminate much of the danger factor for the ranch hands involved in
tending the herd or the assistants who work with bulls during semen collection.
Bulls with good dispositions are also less prone to nervous or challenging
behavior, thus reducing the danger factor for other bulls in the herd and reducing
injuries to cows during breeding.
Reproductive Soundness
An infertile bull is useless for production, but a subfertile bull is also detrimental to
the herd because the offspring he produces are likely to be subfertile as well. A
producer that comes up with several open cows after breeding season will be
wise to suspect subfertility as a cause, and he should check out the bull before he
culls the cows that didn’t get pregnant.
Before purchasing or leasing a bull, or before using your own bull, you should
make sure the bull has been checked for reproductive soundness. The
examination should include making sure his sheath hangs close to his body, with
no prepuce (tip of penis) exposed when it is relaxed, to prevent injuries from
brush and vegetation in the pasture. The testicles should be equal in size, firm
but not hard, free of lumps and scar tissue, and of adequate size for his breed
and age. Brahman breeds generally have testes of smaller circumference (up to
4 inches smaller) than other breeds.
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General measurements of the scrotum circumference for age should fall within
this range:
12-14 months
15-20 months
21-30 months
31+ months
30-34 cm
31-36 cm
32-38 cm
34-39 cm
Breeding Soundness
A bull that has passed the tests for structural and reproductive soundness,
muscling, and temperament is then a good candidate for breeding soundness
testing by a veterinarian. The doctor will give the bull an over-all exam, palpate
the accessory sex glands to check for abnormalities, measure the scrotum
circumference for record keeping, and take a semen sample for analysis. If all
else comes out OK and the semen sample is good, you have yourself a
production quality bull.
Cows and Heifers
Production heifers should be selected from cows that calve early and raise the
largest calves. Ideally, the heifer will herself have a high weaning weight but
then keep a low mature weight so maintenance costs are kept as low as
possible. Heifers should also be evaluated for structural soundness, muscling,
and temperament.
Structural Soundness
Evaluate cows and heifers for their general physical soundness and
conformation, remembering that half of the calf’s genetics will come from the
mother. Heavily muscled cows may have difficulty in calving; light-muscled cows
may not be able to nutritionally and physically support a calf until weaning.
Udder development, both in number of teats and their placement, is important in
productive cows.
Breeding Heifers
After weaning, the heifers should be fed a ration that will allow them to reach
approximately 65% of their mature weight by 14 or 15 months of age. At this size
and age, most heifers should experience heat, or the first estrus. Heifers should
be bred by 15 months of age to calve at two years of age. Heifers that calve at
two years will average one more calf in their lifetime than heifers that do not
calve until three years of age. Some producers believe dystocia, or calving
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difficulty, is lower in heifers that first calve at three years. However, in most
cases the reduction in dystocia does not offset the productivity lost by averaging
one less calf than heifers which calve as two-year-olds. The best way to reduce
calving difficulty is to use bulls with a low birth weight EPD. Smaller calves
cause much less distress than a large calf, particularly in first calf heifers.
Review of Beef Reproduction I
The primary goal of the beef industry is to provide quality meat at a reasonable
price; that means cattle must be produced as efficiently as possible to keep
costs down. Selecting good breeding stock is essential to this goal. Producers
should choose breeds that do well in their environment, and they should give
special attention to selection of their production bull or bulls and to their
production cows and heifers.
Bulls should be structurally sound with good conformation, heavily muscled but
not extreme, and of good temperament. The bull must be fertile and should
have a good performance record, as shown through excellent EPD values found
in the sire summary.
Production cows should be structurally sound with good conformation, sturdily
muscled but not extreme, with excellent udder development and a good
temperament. Heifers should be chosen from cows that calve early and raise
large calves. Heifers should be fed well so they can be bred at about 15 months
of age. Calving difficulties in young heifers can be reduced by using bulls with a
low birth weight EPD.
Section II: Beef Reproduction II
Reproductive Efficiency of the Cow Herd
The single most important trait of the herd is the number of calves weaned per
cow exposed to breeding. Many important technologies have been developed to
enhance the reproductive efficiency of the cow herd and assist in genetic
improvement of the herd. These technologies include: estrous synchronization,
estrus detection, frozen semen and frozen embryos, artificial insemination,
embryo transfer, and ultrasound determination of pregnancy.
Estrus Synchronization
Estrus synchronization is an important factor in managing the cow herd. If the
cows in a herd are in estrus at the same time, the labor required to have a
successful artificial insemination program is greatly reduced. Cows can all be
inseminated on the same day. This allows the herd to be worked only once
rather than several times to breed all the cows. Synchronized estrus and
insemination leads to a shorter calving season. All the cows are bred on the
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same day so they should all calve within several days of one another. This also
gives the producer a uniform weight calf crop at weaning time.
An added benefit of synchronization is to customize the calving operation to fit
the differing needs of first-calf heifers and mature cows. Often, producers bring
all the heifers into estrus about 30 days before the cows, then use artificial
insemination with the semen from a bull with an EPD for low birth weight to
reduce calving difficulties. By synchronizing and inseminating the cows at a later
time, heifers should calve first, allowing the producer to give the first-time
mothers more care and medical attention. Also, the heifers’ calves, which tend
to have a lower birth weight due to first-time calving and use of low weight bull
semen, will have a chance to catch up in weight to the cows’ calves, thus
allowing a more uniform weight calf crop going to market or being placed in the
herd. This staggered breeding also allows heifers an extra thirty days for postdelivery healing before being rebred with the rest of the cows for the next
season. Synchronization can be accomplished with hormone injections with
Syncro-Mate-B, Lutalyse, Bovilene, and Estrumate. Estrus can also be induced
through progesterone implants.
Estrus Detection
Estrus detection is an important factor in breeding programs that utilize artificial
insemination, superovulation, and embryo transfer. Estrus can be detected by
skilled producers through observing behavior. A swollen vulva, discharge,
seeking out the bull, and standing for mating (even by other cows) are symptoms
of estrus in cows, also called standing heat. If a bull or the young bulls in the herd
are persistently following a cow, she may be in very early or very late stages of
estrus. Another indication is the “flehman response” in which a bull raises his
head and curls his upper lip upon sniffing the cow’s vulva or putting his nose into
the cow’s urine stream. The herd should be observed every morning and
evening to accurately detect estrus.
Estrus Detection Aids
There are several heat detection aids available for use when the herd cannot be
observed regularly throughout the day. Both depend on the use of marker
animals to indicate that the cow experiencing estrus has been mounted. A
marker animal is either an androgenized cow (one treated with male hormones
so she acts sexually like a bull) or a gomer or teaser bull (a bull surgically altered,
allowing him to mount the cow but not penetrate and cause pregnancy). The
chinball marker is an estrus detection aid that is attached to the marker animal
and leaves a trace of paint on the back of the cow when she is mounted. KaMaR
pressure patches are applied to the rumps of cows. These patches release
colored ink when they are activated by the pressure of the marker animal
mounting the cow.
Superovulation
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Superovulation is accomplished by injecting Follicle Stimulating Hormone, (FSH)
into the cows. In females during the normal progression of pregnancy, this
hormone causes the development of a single follicle that ruptures and releases
the egg into the oviduct. When given in large doses, FSH causes multiple follicles
to develop and release eggs. This results in the recovery of many eggs that can
be fertilized or frozen and placed into cows as surrogate mothers.
Superovulation allows superior females to produce eggs, which are then usually
inseminated and allowed to grow into embryos before being placed in the
recipient cows in a process called embryo transfer.
Embryo Transfer
Embryo transfer requires a combination of sychronized estrus, superovulation,
and artificial insemination. The donor cow and the recipient cow must have
synchronized estrus. The donor cow is superovulated, then artificially
inseminated. Approximately 6 days after estrus the embryos are flushed out,
evaluated, and placed into the uterus of the recipient cow for gestation. If no
recipient cow is available, the embryos may be frozen and stored or shipped.
Embryo transfer allows several calves from a superior female to be born in the
same year, which expedites progeny testing of females. Before embryo transfer,
progeny testing in females was virtually impossible. The accuracy of a progeny
test depends on the number of offspring an individual has produced. The
individual should have at least 10 offspring to provide an accurate test. A bull may
easily sire the necessary number in a single year, but a cow may not be able to
naturally produce that many calves in her lifetime.
Freezing and storing embryos or semen has facilitated the exportation/importation
of superior quality cattle because although bulls and calves face quarantine,
testing, and holding periods, there are no such restrictions on frozen products.
Another advantage to collecting frozen embryos and semen is that the products
can be easily stored and shipped, and the products can be used long after they
are collected.
Artificial Insemination
Artificial insemination allows producers to breed their cows with superior bulls
that would normally be unavailable to them or would be too expensive for them to
use. The semen is collected from the bull in an artificial vagina and then
evaluated for motility (movement) and morphology (physical structure). The
sperm cells should have a rapid forward motion and should be free of deformities
such as two heads or tails, missing heads or tails, misshapen heads, or curly
tails. If the semen has adequate concentration of sperm cells and the cells are
normal and alive, the semen is deemed acceptable and may be diluted with an
extender fluid and placed into “straws,” each of which will contain approximately
40 million sperm cells. The straws are coded with information, cooled down, and
then frozen for storage or transportation.
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After the semen is thawed, it should be checked under microscope to make sure
that the semen has kept at least 25% motility. Then, the straw is placed into an
insemination gun, the long extension of the gun is passed through the cow’s
cervix (which is relaxed during estrus), and the semen is deposited in the body of
the uterus.
Pregnancy Diagnosis
If a cow has not returned to heat within 21days after insemination, she can be
suspected of having conceived. Because other problems can mimic pregnancy
(such as ovarian cysts, a silent heat, or not noticing the cow came into heat),
cows are considered pregnant if they don’t come into heat within 60 days, or
three estrus cycles. In herds that have two calving times, the cow that did not
conceive may be given a second chance to do so in the second breeding period.
A cow that misses conception twice will probably be culled from the herd.
If the cows were bred through artificial insemination, the whole herd can be
checked at one time, a good time-saving management procedure. Producers
use the previous calving records for the cow, the dates of exposure to breeding,
and pregnancy diagnosis results to help estimate the calving date.
Methods of Pregnancy Determination
Pregnancy diagnosis is most often performed with one of two methods: rectal
palpation or ultrasound.
One advantage of rectal palpation is reduced cost, but accuracy requires both
skill and experience. The technician can estimate the age and development
status of the fetus through reaching through the rectum and feeling the head,
legs, and position of the fetus within the uterus, and the size of the codiledients
(nutrient sacks inside the uterus) that nourish the calf. Palpation is usually best
used in advanced pregnancies.
Ultrasound imaging may detect an early pregnancy that would be missed during
palpation because of the tiny size of the fetus. Ultrasound is able to tell if the
embryo is alive (can see heart beating), and is less likely to cause pregnancy
problems or abortions because it doesn’t physically disturb the embryo.
Review of Beef Reproduction II
In order to make the best use of available technologies, cattlemen must
understand the basic biological processes involved in estrus and the estrus
cycle. The goal is for 100% of the cows to deliver a healthy calf each year. Cattle
producers may choose to use natural breeding using their own or leasing a
quality production bull, or one of the newer reproduction enhancement
technologies to ensure pregnancies.
These technologies include estrus synchonization, methods for estrus detection,
artificial insemination, superovulation, embryo transfer, and freezing and storage
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of semen and embryos. Producers can use ultrasound to detect early
pregnancies, or use rectal palpation after the first trimester to physically confirm
the fetus.
Section III: Beef Reproduction III
Good management practices are the key to making a profit in the cattle business.
Cattle must be healthy so that cows produce quality calves and bulls remain
fertile; heifers must be feed well and cared for so they reach a desired weight for
breeding; calves must be given good attention so they grow healthy and strong.
Health of the Herd
When a cow is open (did not conceive), it is often assumed that the cow has a
fertility problem. However, the reduced calf crop may also be due to a sub-fertile
bull, inadequate nutrition in the herd, or even a disease outbreak that causes
abortion in the cows. The health of the herd is taken care of through good
nutrition, maintaining good body condition, and use of vaccinations to prevent
diseases.
Nutrition
The herd should be given the highest quality food available, whether in forage or
supplement feed. Here is some useful information regarding nutrition in beef
cattle:
50% to 60% of the cost of raising cattle is feed. In young cattle, half of feed goes
to maintenance, half to gain. Steers consume more feed than heifers; heifers are
often over-fattened. Larger exotic breeds gain faster than British breeds but
must be carried to a heavier weight to grade choice (need about 15% more feed).
Brood cows and growing cattle need 1-3 lbs. protein/day. Protein requirements
are low in early and middle gestation (1.5 to 1.7 lbs/day), but increase
substantially before/after calving and during lactation (to 2.5 to 3 lbs/day).
Water needs of cattle run 1 gal/100 lb. body weight in winter (twice that in
summer). Lactating cows need twice as much water as do dry cows.
The major vitamins of concern in beef cattle are A, D, and E. The major minerals
of concern are copper, zinc, manganese, iodine/cobalt, and selenium. Breeding
cattle require phosphorus in their diet (phosphorus should never be higher than
the calcium level). Reduced cow fertility can be caused by low amounts of
selenium, phosphorus, or copper and zinc.
Heifers should be fed to reach a target weight of between 650 and 750 pounds,
or 65% of their mature size, by 15 months of age. This allows them to come into
estrus and be bred to calve at two years of age. Heifers should be bred 30 days
before mature cows and fed separately from cows during gestation to ensure
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they receive adequate nutrition because the heifers are themselves still growing,
plus supporting a calf, and mature cows tend to push heifers away from the best
food.
Nutritional Needs During Pregnancy
Cows and heifers need good nutrition throughout gestation, and up to twice as
much dietary energy from feed 45-60 days prior to calving and after calving and
during lactation. The cow must provide nutrition to the growing fetus through
nutritional nodes called codiledients which grow in the uterus along with the calf.
Cows that don’t receive enough protein in the last 60 days of pregnancy stand a
greater chance of delivering calves born with “weak calf syndrome.” Cows also
need good nutrition—up to twice as much as normal feed, including water--during
lactation so they can supply good milk to the growing calf and in order to be in
good condition to rebreed on time.
Body Condition
The body condition scale ranges from 1 to 9, with 1 being extremely emaciated
and 9 being extremely obese. A score of 5 is the best and a score of 4 or 6 is
acceptable; beyond these scores reproductive efficiency may be compromised.
Body condition is important in all members of the production herd. The bull must
have adequate condition to last through the breeding season. However, if the bull
is too fat, he may be lazy and sluggish and may not cover all the cows. Cows also
should have adequate condition to support a calf to weaning. The cow will use
her fat stores to provide milk for the calf. If she has no fat stores, her reproductive
performance may decrease. The same is true of cows that are too fat; they often
experience reduced conception, and if they do become pregnant, they may have
difficulty calving.
Good body condition can be maintained by feeding the best quality food, whether
forage or feedlot grains or any combination, that is tested so the rancher can
include adequate amounts of vitamins and mineral supplements if they are
needed. Pastures should not be overstocked or overgrazed. Care should be
taken that mature cows don’t push pregnant heifers away from the best food.
Protein supplements such as soybean meal, urea, ammonia, brewer’s grains,
cottonseed meal should be kept high quality until calves reach at least 600
pounds; after that, the source of protein is not as important, and cheaper forms,
such as urea, can be used.
Vaccinations
The health of the production herd can be safeguarded by protecting them against
infectious diseases. The cow herd should be vaccinated against diseases such
as Brucellosis, Infectious Bovine Rhinotracheitis IBR), Bovine Virus Diarrhea
(BVD), Leptospirosis, and Vibriosis, which can all cause reduced fertility and
spontaneous abortion. Confer with your veterinarian for the protection most
needed in your area of the country.
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Cows should be vaccinated 6 to 10 weeks before delivery so the protection is
passed on to their calves through the first milk—their colostrum.
Breeding Program
Reproductive efficiency is determined by the number of calves weaned per cow
that were exposed to breeding. The goal is 100% of cows and heifers pregnant
each year. A cow that does not conceive within two breeding opportunities is
usually culled. Producers can reach closest to the reproductive efficiency goal by
paying strict attention to management practices that increase the fertility of the
bull and through using quality replacement heifers.
Reduced Reproduction
If there are several cows that remain open, the producer should first check the
fertility level of the bull. If the bull checks out OK, then producers should check
the nutritional levels of the cattle to be sure their diets include sufficient amounts
of phosphorus, zinc, and manganese because feeds and forage low in these
minerals can cause reduced fertility. Also check pastures or range lands to be
sure there are no poisonous plants or plants which, at certain levels of ingestion,
can cause spontaneous abortion, because a few of these “open” cows may
actually have aborted early in pregnancy.
If you have a cow that comes up open, yet you are pretty sure she conceived,
she may have had an embryonic death. Embryonic death rate is fairly high, from
10 to 20% of all pregnancies. In this case, the egg was fertilized and an embryo
created, but the embryo did not attach to or implant in the uterine wall. If the
embryonic death occurred in the first two or three weeks of fertilization, the cow
will most likely return to a normal estrus cycle. If the death occurs later, then the
cow will seem to have an extended heat cycle, when she had actually been
pregnant.
Bulls
Fertility in the bull is critical to the success of any breeding program. If the bull is
infertile, the quality of the cows won't matter. When a cow is open, it is often
assumed that the cow has a fertility problem. However, the reduced calf crop may
be due to a subfertile bull. Fertility in bulls can be influenced by the weather, age
of the bull, illness, structural soundness, and nutrition. Around four years of age,
fertility in the bull tends to peak. Many bulls are adequately fertile until 7 or more
years of age, but age tends to affect fertility. Nutrition is also important to the
fertility of bulls, and quality of the feed is as important as the quantity. Many
producers have found that a deficiency in vitamins and minerals can cause
reduced fertility in their herds. Therefore, they supplement the diet with mineral
and vitamin blocks or fortified feeds.
Structural soundness of the bull is important because he must be able to travel
the distances necessary to cover all cows. If a bull is expected to cover too many
cows, the bull may not be able to locate all the cows that are in heat at one
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particular time, or he may be overworked and suffer a low sperm count. Extremely
hot weather or a prolonged fever may reduce the sperm count of a bull for 6 to 10
weeks. The testes must remain about 4 to 5 degrees below body temperature to
produce sperm properly. The loss of sperm production will cause the bull to be
infertile for as long as the temperature stress lasts plus the amount of time it takes
for new sperm cells to be produced and mature. A breeding soundness exam will
tell the producer if the bull is fertile and able to breed the cows in the herd.
Replacement Heifers
First-calf heifers are bred 30 days before mature cows so they calve earlier and
have more time to heal after calving; then they are rebred at the same time as
the rest of the cow herd. The average gestation of cattle is 283 days and it takes
approximately 45 days to heal after calving. That leaves 37 days in which to
rebreed the cow so she calves every 365 days. This extra time gives the heifers
67 days to become pregnant again and calve with the rest of the herd the next
year. The best way to decrease calving difficulty is to breed heifers to bulls with a
low birth weight EPD. A smaller calf will be less likely to cause distress, provided
that the presentation of the calf is normal.
Calving
Many cattle producers give their pregnant cows additional vaccinations about 60
days before delivery to assure that maximum protection is passed on to the
newborn. Near the projected calving date, heifers should be observed closely.
Experienced persons should be ready to assist if the heifer needs help, and they
should know when to call for medical assistance when it is needed. Cows about
to deliver will look for a spot away from the herd, and usually mature cows can
handle the delivery process by themselves.
Signs that Parturition is Near
When a cow is nearing delivery time, the udder will be enlarged, with possible
dripping of colostrum; the hindquarters will be quite droopy-looking as the pelvic
ligaments relax; the mucous plug will be expelled, leaving a slight discharge
seepage. If the cow is birthing in a stall, provide clean straw bedding shavings
may be too small and can get into the calf’s lungs. Generally, leave the cow
alone, but be nearby if she needs help.
Parturition
Calving progresses in three stages: labor, delivery, and expulsion of the fetal
membranes.
Labor
The preparatory stage, or labor, is marked by uterine contractions about
every 15 minutes and dilation of the cervix. This stage may last up to 24
hours, but usually ranges between 2 and 6 hours. During this time, the cow
may get up and lay down repeatedly, stand with her tail up and her back
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arched, and kick at her stomach. This stage ends when the calf moves
into the birth canal and the water bag ruptures.
Delivery
Contractions come every two minutes and the cow’s abdominal muscles
begin to actively push the calf from the birth canal. The front feet are
delivered first, with the head resting on top of the legs. The remainder of
the body will then be quickly pushed out. If only one leg appears, or if the
head seems to be bent backward, you may be able to reposition the calf so
that delivery can proceed. If it is still intact, tear the sac from around the
calf’s head, but do not cut the umbilical cord. The cow and calf will break
the cord themselves as they move around. Delivery may last up to 4 hours
without harm to the calf if the umbilical cord is still intact. If 3 or more hours
pass with no apparent progress, the cow may be experiencing dystocia,
and assistance might be needed.
Dystocia is a complication in delivery caused by pelvic problems or
muscle contraction problems (maternal dystocia) or malpositions or
malformations of the fetus (fetal dystocia). The leading cause for dystocia
in a heifer during delivery is a calf that is too large to pass through the
pelvic opening. That is why it is best to use low-birth weight bulls for firstcalf heifers. If pulling the calf as the cow has contractions is not effective
within a half hour, professional help should be sought. It may be necessary
to perform a Caesarian section to get the calf out.
Expulsion of the fetal membranes
The third stage, expulsion of the fetal membranes, should be complete
within 8 to 12 hours or the placenta may cause an infection. The placenta
should be examined to ensure that all of it has passed from the cow. If the
placenta is not delivered, do not pull the afterbirth from the uterus or you
may cause damage. Get medical help to increase the cow’s uterine
contractions so she can expel all the afterbirth. Retained placenta can be
caused by low selenium, low vitamin A, or low amounts of copper or iodine
in the diet.
Post-Delivery Care of the Cow
Make sure the cow was not injured during the delivery process. Many ranchers
give cows a tetanus antitoxin injection to help protect against infection while the
cow is in the recovery period. Give the cow increased amounts of quality food
and water so she can produce the milk needed to support the growing calf.
During the healing period, check the cow for post-delivery problems. Although
not as common in beef cows, she may also need to be checked for inflammation
of the uterus (metritis). Check on the cow during the next few days to make sure
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she doesn’t develop Pyometra, a problem that occurs after birthing when the
cervix closes, preventing drainage of infected material from the uterus. Pyometra
can lead to sterility.
Post-Delivery Care of the Calf
After the calf is delivered, it should be checked to be sure that it is able to
breathe. Clear air passageways of any mucous if necessary. If the calf is not
breathing, try tickling the inside of the nostrils with a feather or finger to cause a
sneeze or intake of air. If the lungs are filled with fluid, lift the calf by the hind
legs to try to drain the lungs. If the calf still does not breath, try lifting and
lowering the front legs to draw air into the lungs, much like CPR in humans.
Treat the navel with a solution of iodine or similar disinfectant to prevent infection.
Within the hour, the calf should be able to stand and will begin searching for his
or her first meal. The calf should nurse 3 to 6 pints of the first milk, called
colostrum, which contains Vitamin E which the calf needs and antibodies to the
diseases to which the cow has been exposed. After 24 hours, the antibodies are
no longer absorbed, so if the calf will not suckle, try to get the calf to drink milk
with colostrum from a bottle. Milk with colostrum can be captured from the
mother before calving and frozen to be used in such cases, it can be captured
from a cow that has also just given birth and whose calf is suckling well, or it can
sometimes be purchased in frozen or powder form.
Review of Beef Reproduction III
There are many factors affecting the reproduction in a cow herd. Good
management practices are the key to improving the efficiency and productivity of
the herd.
Cattle producers should make sure their cattle are vaccinated against diseases
which could reduce fertility or cause spontaneous abortion in cattle. The cattle
should be fed well, with supplements if needed, to maintain a good body
condition and prime reproductive ability. Cows and heifers should receive good
nutrition during pregnancy so they can support the growing calf. Heifers should
receive extra nutrition because they are not only supporting a growing calf, they
are still growing as well.
When the time comes for rebreeding, do not overfeed the still-lactating mothers,
because obesity can cause reduced conception and birthing problems with the
next calf. Heifers are usually bred 30 days before mature cows so they can be
helped during delivery and so they have an extra 30 days to heal before their
next rebreeding along with the other cows after calving.
Dystocia in heifers can be reduced by using bulls with low birth-weight EPDs.
Cows will usually take care of parturition themselves, but you should be nearby in
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case difficulties arise. If you do have to give assistance, make sure you, any
equipment, and the vulva of the cow are kept as sanitary as possible to reduce
the risk of infection. Make sure the cow expels the entire placenta so it doesn’t
cause uterus infections, which may in turn cause permanent sterility.
Make sure the calf is uninjured, breathing and drinking colostrum within the first
hours and the next two days. The colostrum gives the calf protection against
diseases and calves are born with low amounts of vitamin E, a vitamin found in
the colostrum.
Anatomy
Male
Testes
The testes are the site of sperm production. The testes are also
responsible for secretion of the male hormone testosterone. Testosterone
controls the expression of the secondary sex characteristics in bulls (such
as the crest, or hump and deep voice).
Scrotum
The scrotum is a fleshy sack surrounding the testes. The scrotum provides
protection from the outside environment. The testes are most productive
at a temperature of 4 to 5 degrees below the normal body temperature of
the bull. The cremaster muscle in the scrotum will contract to bring the
testes closer to the bull's body when outside temperatures are cold. During
hot weather the muscle will relax to allow heat to escape from the testes so
that the temperature does not rise to levels that would compromise sperm
production. If the bull has a prolonged fever the sperm production of the
bull may suffer.
Epididymis
Duct leading away from the testis to the vas deferens. The epididymis is
the site of storage and maturation of the sperm cells.
Vas deferens
Passage for sperm from the epididymis to the urethra in the pelvic area.
Urethra
(not shown) The single duct that leads from the vas deferens, near the
accessory sex glands, to the end of the penis. Serves as an excretory duct
for semen and urine.
Accessory sex glands
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Provide fluids essential for formation of the semen and for assuring
optimum motility and fertility of the sperm. The accessory glands include
the bulb urethral, prostate and vesicular glands. The fluids contribute
fructose, a source of energy for the sperm cells. The fluids also serve as a
buffer to protect the sperm cells from the slightly acidic environment of the
vagina.
Penis
Male organ of copulation.
Sigmoid flexure
S-shaped bend in penis that allows the penis to be drawn completely into
the body. Straightens during copulation.
Retractor penis muscles
Smooth muscles that relax and allow the sigmoid flexure to straighten and
the penis to be exposed.
Sheath
Loose skin that encloses the free end of the penis.
Anatomy
Female
Ovary
Essential organ of reproduction in the female. The ovary produces the
hormone estrogen, which is responsible for the expression of female
secondary sex characteristics (such as the development of mammary
tissue). The ovary also produces progesterone (via the corpus luteum)
during mid- estrous cycle and pregnancy. The ovum or egg is released
from the ovary in a process called ovulation.
Oviduct
Tubular structure that serves as the passageway for the egg after
ovulation. The oviduct is also the site of fertilization.
Fimbria
Funnel-shaped opening of the oviduct that covers the ovary and catches
the egg at the time of ovulation and funnels it into the oviduct.
Uterus
Site of fetal growth and development. Also called the womb. Consists of
the uterine body and the uterine horns. The embryo will attach or implant
itself to the wall of the uterine horn approximately 6 days after fertilization.
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Cervix
The cervix is a muscular ring that serves to close off the uterus from debris
or bacterial pathogens that may cause harm to the fetus. The cervix
relaxes during estrus to allow passage of the sperm into the uterus after
breeding.
Vagina
The area where copulation occurs. The semen is deposited in the vagina
and travels through the cervix and into the uterus and oviduct.
Vulva
The vulva is the external portion of the female reproductive tract. Consists
of labia and clitoris.
Clitoris
The clitoris is homologous to the penis in the male; that is to say, they
arise from the same embryonic tissues.
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Vocabulary
Atresia: absence or disappearance of an anatomical part (such as an ovarian follicle)
by degeneration.
Conceptus: the fertilized egg, embryo or fetus.
Estrous cycle: regular pattern of changes a body goes through from one estrus to the
next(approximately 21 days in the cow); may be interrupted by pregnancy or
manipulated through hormone treatment.
Estrus: the period of time when the female is receptive to breeding and is able to
conceive; lasts 6-14 hours and occurs approximately every 21 days.
Gametes: male or female germ cells; sperm or egg.
Gestation: carrying of the young in the uterus; pregnancy.
Morphology: the physical structure of the sperm cell.
Mortality: the percent of dead sperm in a sample.
Motility: the ability of the sperm cell to make rapid forward progress.
Parturition: the act or process of giving birth to offspring.
Perivitelline space: the space between the vitelline membrane and the zone pellucida.
Vesicle: fluid filled space or pocket.
Vitelline membrane: the cell membrane of the ovum.
Zona pellucida: the heavy membrane that surrounds the ovum after ovulation.
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