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Beef Cattle ReproductionAnatomy and Physiology
Whitney A. Whitworth
Associate Professor of Animal Science
University of Arkansas at Monticello
Improve reproductive efficiency
Production of young is primary determinant of income for most livestock species
A 3% improvement in birth rate would result in an additional 1 million beef calves per year
Introduction
Reproduction is a tremendously coordinated process, mainly between anatomy and endocrine functions
Basis for reproduction is the gonadFemale: ovaryMale: testis
Puberty
Transitional state after which animals are able to reproduceMost important signals are weight and ageNutritional stress and season of year are also
importantAfter puberty, an animal is said to be
reproductively competent
Puberty
Associated with development of secondary sex characteristics Hump on necks in males,
increased musculature, voice changes
Addition of body fat in females, mammary development
Endocrinology
Endocrine cues are initiated by the hypothalamusSmall area in brain which releases GnRH
Released in an episodic manner, travels to the anterior pituitary gland
Anterior pituitary gland releases LH and FSH Travel to the gonads of both males and females
Relationship between hypothalamus and pituitary gland
Bearden and Fuquay, 2000
Endocrinology LH: Luteinizing hormone
Induces ovulation & development of the corpus luteum
Aids in the maturation of the follicle and spermatozoa Stimulates testosterone production in the male
FSH: Follicle stimulating hormone Induces follicular development Induces estrogen production Stimulates spermatogenesis
Endocrinology
After ovulation, follicle turns into corpus luteum (CL)Primary function is progesterone production
Required for maintenance of pregnancy Progesterone inhibits FSH and LH production Reduced excitability of smooth muscle fibers Negative feedback to the hypothalamus
Endocrinology
Estrogen: This follicular hormone is responsible for: Estrus Influence mobility and secretory function in the
reproductive tract Responsible for early stage development of the
mammary gland Follicles produce estrogen, causing an LH surge
LH surge causes ovulation
Endocrinology
Oxytocin: secreted by the posterior pituitary and the corpus luteum causes contractions of smooth muscle fibers. This is involved in: Milk “let down” Uterine contractions during parturition Contractions of smooth muscle in uterus and oviducts during
mating Prostaglandin: Produced by the endometrium of the non-pregnant
uterus. Causes the regression of the corpus luteum
Causes uterine contraction
Female Anatomy
Consists of ovaries, oviducts, uterus, cervix, vagina, and external genitaliaSuspended below the rectum by various
ligamentsOvaries:
Responsible for storage, development, and release of ova
Produce progesterone and estrogen
Female Anatomy Ovaries
Contain all of the ova (eggs) the female will ever have in her life
Ova develop into follicles during the monthly estrous cycle of the female
Follicles either continue to grow or undergo atresia
Upon ovulation, follicle is captured by the infundibulum
Directs ovum to oviduct, sight of fertilization being the ampullary-isthmic junction
Female Anatomy
Oviduct is connected to the uterusOvum will reside in oviduct for approx. 3-6
days before traveling into uterus Cattle have bipartite uterus
Short uterine horns, small uterine body
Uterine function to provide passageway for sperm, protect fetus, and expel fetus during parturition
Female Anatomy Cervix has following functions:
1. Passageway for sperm cells 2. Storage reservoir for sperm cells 3. Barrier between external and internal environments 4. Provide lubrication 5. Passageway for fetus during parturition
Under influence of high progesterone, cervix is closed off
Female Anatomy
VaginaServes as copulatory organ is most speciesConnects cervix with vulva
Blind pocket
Labia Majora
Ovary
Cervix
Vestibule
Vagina
Vulvo-vaginalsphincter muscle
Clitoris
Urethra
Bladder
Oviduct
Uterine Horn
Uterine Body
Uterus
Ovary
OviductBroad LigamentCervix
Bladder
Pelvis
VaginaVulva
Rectum
Male Anatomy
Primary structures of the male reproductive tract are:TestisPenisDuct systemAccessory sex glands
Male Anatomy
Testis – responsible for both sperm production and sex steroid productionFor sperm production, scrotum must be 4-6
degrees below body temp. If one or more testicles do not properly
descend into scrotum, cryptorchidism is result Have secondary sex characteristics, but usually no
sperm production
Male Anatomy
Testes are suspended by the spermatic cord into the scrotumScrotum contains thermosensors
Can induce sweating Cause increased respiration rate Cremaster muscle can raise or lower testes, with aid
of tunica dartos muscle Also contains a special vascular system called the
pampiniform plexus
Male Anatomy
Both sperm and testosterone made in the testisTremendous potential for gamete production
in the male Produced in the seminiferous tubules, migrate to
epididymis Three functions of epididymis: storage, transport, and
maturation
Male Anatomy Prior to ejaculation, sperm travel from the
epididymis through the ductus deferens to urethraDuctus deferens can be cut in procedure called
vasectomy Accessory sex glands produce fluids which are
added to sperm to make semenThree glands are: the vesicular glands, the prostate
gland, and the bulbourethral glands
Male Anatomy Penis is organ which deposits semen into the
female (either vagina or cervix depending on species)Farm animal species either have a vascular
(stallion) or fibroelastic (bulls, boars, rams) penisFibroelastic penis exists in S-shape within the body
of the male until erection When erection takes place, muscles relax and allow
penis to extend outside the body
Cowpers Gland
Caput Epididymis
Cauda EpididymisTestis
ScrotumGlansPenis
RetractorPenis Muscle
SigmoidFlexure
BladderAmpulla
Seminal VesiclesProstate
Rectum
Vas Deferens
Tunica Albuginea
-
Spermatic Cord -
Caput Epididymis
Rete Testis
Cauda Epididymis
CorpusEpididymis
Vas Deferens
Blood supply in testis aids in cooling
1. Pampiniform Plexus Counter-current heat exchange causes a cooling of arterial blood supply Single artery surrounded by a network of veins (Increased surface area)
2. Convoluted testicular artery on surface of the testis In Ram temperature decrease 40C before entering testis
Scrotum, testis and spermatic cordare all involved in thermoregulation
PampiniformPlexus
TesticularArtery
Pregnancy
Successful timing of ovulation and mating should result in pregnancyFemale is receptive to male during estrus,
encouraging copulationWindow of opportunity for fertilization is
narrow If has not occurred within 12 hours of ovulation,
ova begins to degenerate
Pregnancy
Fertilized oocyte is called a zygoteCell division begins soon after fertilization
Stages: zygote morula blastocyst Blastocyst is free-floating and moves down oviduct
to uterus Day of implantation occurs between days 18 and
22 Inner cell mass of blastocyst becomes fetus and
trophoblast becomes placenta
Pregnancy
High levels of progesterone are required for pregnancyPregnancy must be recognized by female to
prevent degradation of the CL Maternal recognition of pregnancy signals:
Cow and sheep = IFN-
Pregnancy
Trophoblastic cells give rise to placenta Fetal membranes include the amnion, chorion, allantois,
and the yolk sac Placenta regulates exchange of oxygen, nutrients, waste, and
in some cases, antibodies
When more than one fetus is present, the fetal membrane fuse together If bovine twins are of differing genders (one male and
one female), female will be sterile Condition is called Freemartinism
Pregnancy
Approximately 2/3 of fetal growth occurs in the last trimesterEnergy demands are the highest during this
time Pregnancy averages 283 days in beef
cattle
Parturition
Process of giving birth Initiated by hormone secretions of the fetus
Caused by fetal stress
Parturition
Most births occur naturally with no assistanceMalpresentations and inappropriate size of
offspring may necessitate intervention Dystocia = difficult birth
Major cause of dystocia is size of fetus
Parturition
Females preparing to give birth demonstrate behavioral changesBecome restless, separate from others, show
discomfortUdder becomes engorged, vulva begins to
swell
Parturition
Birth occurs in three stages:Stage I = initiation of myometrial contractionsStage II = expulsion of fetus
Must be completed in a timely manner
Stage III = expulsion of placenta May take up to several days
Parturition
Following birth, most animals clean their young and bond with them
Critical for young to eat ASAP so that they get colostrumContains maternal antibodies and is
responsible for first immunityGreatly increases rate of survival of offspring
Parturition
Interval between parturition and onset of estrus activity is called postpartum or postpartum intervalCattle must become pregnant within 80 d after
birth to ensure a yearly calving intervalGreatly affected by poor nutrition, and
presence of suckling offspring
Environmental Influences on Reproduction Nutritional effect can influence female’s ability to
get pregnant and male’s ability to exhibit libido Primary nutritional limitation on animals is
energy Female loses ability to become pregnant as she loses
body fat Also, if a female is too fat she may fail to conceive
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