physiology of reproduction

Unit 1: Physiology of Reproduction

• The objective of unit 1 will be to create an understanding of reproduction from the physiological perspective.

• Topics covered in this unit:– Male and Female anatomy– Hormone Function– Pregnancy – Parturition– AI– Reproductive Technologies


• Unit 1 will cover Chapters 10 + 11

• Why is knowledge of the fundamentals of reproduction crucial?

• Female reproductive organs and function– Ovary

• Produces the ova & female sex hormones (estrogen & progesterone)

– Folliculogenesis• Each follicle contains an ovum• Development starts from deep within the ovary

with primordial follicles• As a follicle develops, it produces more estrogen,

which continues its maturation


• Folliculogenesis cont.– Each follicle goes through stages of

recruitment, selection, and dominance.– As a follicle develops it can become:

• Primary• Secondary• Tertiary• Graafian• Degenerative (atresia)


• Folliculogenesis cont.– Only the Graafian follicle can be ovulated– Ovulation occurs when the follicle ruptures, releasing

the ovum– After ovulation, follicular cells form the Corpus Luteum

• The Corpus Luteum– “yellow body” or callous on the ovary– Produces progesterone (maintains pregnancy)


• The Oviduct– Collects the ovulated ovum in the

Infundibulum which guides the egg into the oviduct

– The site of fertilization– A fertilized embryo migrates to the uterus

within 3-5 d


• Uterus– Embryo attaches to the uterine wall to begin

development– Some attach in the uterine horn (sow), others

in the uterine body (cow/mare)– Guarded by the cervix (gatekeeper)


• The Vagina– The “passageway” to the reproductive tract– Female organ of copulation– Environment changes depending on the stage

of reproductive cycle– Also include the urethra


• Male Reproductive Organs– Testicles

• Suspended from the body• Produce testosterone

– Leydig or Interstitial cells

• Site of spermatogenesis– Sperm begin development within the seminiferous

tubules


• The Epididymis– Stores sperm for maturation– Acquire the potential for fertilization– Most mature spermatozoa are nearest the

Vas Deferens, while least mature are nearer the testicles

– Some degenerate and are reabsorbed


• The Scrotum– Two-lobed sac– Serves two purposes:

• Protection• Temperature regulation

– Can be 3-13º cooler than body temp.

– Tunica Dartos & cremaster muscles• Responsible for raising and lower the scrotum

– Pampiniform plexus• Acts as heat exchanger to cool blood as it enters the scrotum

– Begins functioning at puberty w/ hormone function 40-60d prior to puberty

– What happens if this malfunctions?


• Vas Deferens– Transport tube for sperm from epididymis to

urethra.– Spermatozoa are stored in the ampulla of the

V.D. until the time of ejaculation– Some species deposit sperm very quickly,

and some slowly (8-12 min.)• Bull, horse, ram• Boar, dog


• Urethra– Canal extending from the bladder through the

pelvis to the end of the penis– Carries both urinary waste and sperm

• The penis– Male organ of copulation– Virtually every species is different in form and

function


• Male Hormone Function– Hormones stimulated and produced from the

Anterior Pituitary of the brain1. Luteinizing Hormone (LH)-causes Leydig cells to

produce testosterone

2. Follicle-Stimulating Hormone (FSH)-stimulates the seminiferous tubules to nourish developing spermatozoa

– Hormone function can be influenced by photoperiod (day length)


• Female Hormone Function– Originate in the Hypothalamus and the Anterior

Pituitary• Gonadotropin Releasing Hormone• LH• FSH

– Some Hormones also released from the female reproductive organs

• Estrogen-follicle• Progesterone-CL• Prostaglandin-uterus


• All these activities make up the estrous cycle– Estrous cycles range from 14-29d and can

last anywhere from 12 hrs. to 9d

• Hormone function can be altered or stimulated with hormone therapy treatments


• Pregnancy– Onset of gestation following fertilization– Embryonic cell division every 20 hrs.– The period of attachment in the uterus is

critical (20-30d cattle, 14-21d swine)-if no attachment-embryonic death occurs

– Embryonic stage ends around 45d after period of formation of major organs

– Fetal stage from 46d to birth


• Parturition– Placenta is responsible for protecting the

fetus and exchanging nutrients and waste with the mother

– Birthing is initiated with the release of cortisol– Cortisol release causes progesterone to

decrease and estrogen, PGF2a, and oxytocin to spike initiating uterine contractions

– Relaxin also released from the CL-stimulates the pelvis


• Parturition cont.– Abnormal birthing (dystocia) can result from

several problems• Size of fetus• Abnormal presentation• Size of pelvic opening


• What has Artificial Insemination done for the livestock industry?– How does it fit?– What are the drawbacks?– Is it prominent in all of animal agriculture?


• Artificial Insemination– First recorded in dogs in 1780, cattle & horses

in the early 1900’s– Can increase the number of offspring from

one male• Bulls – 30-50 females/yr natural, 200-400 units/wk

for AI (avg. 1 calf/1.5 units semen)

– Success of AI dependent on success of estrus detection, quality semen, semen handling, high fertility


• Semen Collection & Processing– Collection of semen w/ and artificial vagina– Male mounts a female in estrus, or trained to mount

an object– May also collect semen manually (boar, dog), or by

electroejaculation– Collection timing

• Bulls – 2x/d, 2d/wk• Boars – every other day• Shortening or extending the schedule may decrease number

of sperm/ejaculate


– Evaluated for:• Volume, sperm concentration, motility,

abnormalities

– Mixed w/ an extender to dilute for more volume (milk, egg yolk, buffer)

– 1 unit of cattle semen should contain 10m normal, motile spermatozoa

– Can be stored and used fresh for only 24-48 hrs.


– Freezing semen• What is it frozen in?• Bull semen – can be frozen and stored for

indefinite time without loss of fertility• Boars, stallions, rams – only modest success w/

frozen semen

• Inseminating the Female– Conception rates depend on:

• Estrus detection, properly managed semen, timing of insemination, insemination techniques, avoiding stress


– Estrus Detection• Signals time of ovulation, timing of insemination• What is the best indicator?• What are some other indicators of estrus?• What are some technologies that might be used to

detect estrus?• What strategies might we use to detect estrus?

– Timing of Insemination• Duration of estrus and timing of insemination

varies w/ species• Exhibition of estrus doesn’t necessarily include

ovulation– Sows at 3-5d after farrowing


• Insemination should occur as close to ovulation as possible

– What is the rule of thumb in cows/sows?

• How common is AI?– What industries use it the most?– Which ones use it the least?

• Estrous Synchronization– Controlling the estrous cycle and the female

expression of estrus


– Why use estrous synchronization?– Where is it the most appropriate and cost

effective?– Prostaglandins

• Causes regression of a CL• Cows will be in estrus ~3d after injection• Only effective in the presence of a functional CL• Heifers/cows must be in d 5 – 18 of estrous cycle


• One-injection system– Observe heats for first 5d of breeding season and AI all

that exhibit heat– Inject those not exhibiting heat on day 6– All animals bred by day 11– Can increase P.R. from 30-40% to 50-60%

• Two-injection system– Inject all cows at day 1 and day 14– All cows should exhibit estrus by day 19, or breed 76-80

hrs. after second shot

• Can be a good tool in well-managed herds• What is a major risk w/ using Prostaglandin?


– MGA & Prostaglandin• MGA – feed additive that suppresses estrus in

heifers• Feed MGA for 14d, give Prostaglandin 19d after

last MGA feeding– Most heifers should show estrus in 48-72 hrs– Conception rate may be >80%

– Select-Synch• Injection of GnRH 7d following Prostaglandin

– Heat detect 24-36 hrs to 5d after injection– Should have ~70% exhibit estrus


– Co-Synch• GnRH on day 0, Prostaglandin on day 7, second

GnRH on day 9 and breed• Initiates ovulation• May not exhibit estrus

– CIDR-B• Use of intravaginal progesterone implant for 7d• Inject prostaglandin on day 6• Breed upon estrus detection from days 3-6 after

injection


– PG 600• Pregnant mare serum gonadotropin• Enhances fertility efficiency in swine• Helps lower days returning to estrus after

farrowing, schedule breeding

– Natural estrus synchronization• Most females will suppress estrous while nursing

young• Removal of calf/piglet will help bring the cow into

heat


• Embryo Transfer– What is ET?– Why use ET?– Can be costly - ~$1000/hd– Superovulation

• Increase the number of ovulated ova• May increase the number of harvested embryos

– How is ET performed?– What components are essential?


– Sexed Semen• What are the advantages/disadvantages?• Reliability of 85-90%


• Unit 1 Assignment– Chapter Review questions pgs & 209

• Pg. – 1, 2, 4, 7, 8, 9, 14, 16, 17, 18• Pg. 209 – 2, 3, 5, 8, 9, 12• Each question will be worth 2 points

– Bonus Question-What is the process of follicle development called? (2 pts.)

– Due at the beginning of the next class period– E-mailed homework is encouraged—please include

the course name/number in the subject line.


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physiology of reproduction