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