farm animal reproduction

FARM ANIMAL REPRODUCTION

The Estrus Cycle

Consists of proestrus, estrus, metestrus, diestrus and anestrus

1. proestrus- begins after corpus luteum regression, ends at the onset of estrus. During this period there is rapid development of the follicle which leads to ovulation and the onset of sexual receptivity

2. estrus- time of sexual receptivity, may be referred to as heat. Ovulation usually, but not always, occurs at the end of estrus.- Some species, like cats and ferrets, are

induced ovulators3. metestrus- the early postovulatory period during which the corpus luteum begins development

4. diestrus- the period of mature luteal activity which begins about 4 days after ovulation end ends with regression of the corpus lutem.5. Anestrus- without estrus cycles

The Endocrine System of reproduction

Hypothalamus- Located in center of brain, next to

pituitary gland. Considered a master gland that controls the pituitary gland

- Releases FSHRH ( follicle stimulating hormone releasing hormone) which acts on the anterior pituitary

Anterior pituitary- In response to FSHRH releases FSH

( follicle stimulating hormone)- FSH acts on the ovary

Ovary- In response to FSH it begins to develop a

follicle- Follicle is like a small blister on the ovary

and contains a maturing egg- Follicle produces estrogen which causes

the animal to come in heat ( estrus)- Estrus in cows is about 18 hours

Hypothalamus- Produces GNRH gonadotropin releasing

hormone when estrogen has been present for a sufficient amount of time

- Causes the anterior pituitary to release leutenizing hormone ( LH)

Anterior pituitary- Releases LH in response to GNRH- LH causes the follicle to rupture leading

to ovulation

Ovary- Rupturing of the follicle occurs with low estrogen

and high leutenizing hormone- Egg released into the oviduct ( occurs 12-24

horus after estrus in cow)- Menstrual bleeding may occur but not in every

estrus- Corpus luteum is formed out of the remaining

follicle- Most successful artificial insemination is done 12

hours after the beginning of estrus ( so insemination precedes ovulation)

Corpus luteum- Yellow body made up of remaining follicle

tissue- Formation is initiated by the LH surge- Produces progesterone which maintains

the lining of the uterus for possible implantation

- If implantation occurs the placenta in the cow will continue to produce progesterone to maintain the pregnancy until birth

Not pregnant- The corpus luteum only lasts about 3

weeks so if implantation does not occur, the lining of the uterus will be sloughed and replaced

- The uterus will produce prostaglandins if not pregnant ( help the uterus to contract)

Ovary ( if not pregnant)- The prostaglandins produced by the

uterus if not pregnant ( 14 days after ovulation) will travel to the ovary and cause lutealysis

- The corpus luteum will be destroyed which will drop the progesterone level

- The dropping of the progesterone level will let the animal come back into estrus

Pregnant animal- First the corpus luteum secretes

progesterone and continues to do so throughout most of the pregnancy

- Then the placenta takes over to maintain pregnancy

- Implantation takes 5 weeks in cattle and horses

Placental types

Diffuse placenta- in horse and pig Cotyledonary placenta – in ruminants Zonary placenta- in dogs and cats Discoid placenta- in humans and

monkeys

Female reproductive hormones

Follicle stimulating hormone ( FSH) – follicle development/maturation

Luteinizing hormone (LH)- ovulation Estrogen- behavioral signs of estrus,

psychic heat, attracting male, accepting male

Progesterone- prevents ovulation/maintains pregnancy

Oxytocin- uterine contractions, milk letdown

Bovine- Polyestrus all year long- Beef cattle spring calving, minimizes

labor costs- Dairy cattle, year round calving for milk

production

Equine- Seasonally polyestrus in spring and

summer - Ovarian activity increases with increased

day length- Ovarian activity can be

induced/manipulated with artifical lighting

Porcine- polyestrus all year long Ovine/caprine- polyestrus fall/winter

Estrus

Vaginal discharge, blood tinged or otherwise is not associated with estrus

14-28 day estrous cycle with 21 days being the average

Length of estrus ranges from 6-24 hours with the average being 15 hours

Time of ovulation is 24-32 hours after onset of estrus

Detection of estrus

Proestrus cows will mount estrus cows Gomer bulls ( penis surgically redirected

out of lateral aspect of prepuce to prevent breeding) will detect females in estrus

Veterinary Manipulation

Prostaglanding F2 alpha- lyses corpus luteum to bring animal into estrus

Progestogen ( regumate) synthetic progesterone- suppresses ovaries, prevents estrus, aids in pregnancy maintenance

Human chorionic gonadotropin, comparable to LH to induce ovulation

Oxytocin- induce labor Dexamethasone- induction of labor Artificial light- alteration of day length

Breeding

Natural cover- Male and female must be present and

capable of breeding- Limits potential progeny- Risk of physical injury to male or female Pasture breeding Hand breeding

Artificial insemination

Increased breedings per ejaculate Semen extender used Disease control Trained personel required Males do not need to be maintained on

farm

Embryo transfer

Allows multiple pregnancies per breeding season

Successful reproduction of physically compromised animals

Donor female can still compete Recipient dam just carries the baby,

shares no genetic material with fetus Used to create number of genetically

similar individuals

Embryo transfer technique

Estrus synchronization of donor and recipients

Superovulation of donor by FSH administration 40 hours prior to estrus

Insemination hand breeding or artificial insemination

Embryo collection established post insemination

Embryo transfer technique

Balloon catheter established proximal to cervix

1-2 liters of buffered saline infused into cervix

Gravity used to recover saline and embryos

Embryos caught by in line filter Embryo evaluation/processing Embryo delivery to recipient dam

Male breeding soundness evaluation

Overall physical condition Breeding history Semen analysis Semen collection Scrotal circumference Libido/reproductive behavior

Female breeding soundness evaluation

Overall physical condition Breeding history Rectal palpation Ultrasound Uterine culture Uterine biopsy Endoscopic exam of uterus Serum hormone assays

Pregnancy detection

Failure to return to estrus Rectal palpation early in cow by palpating a

CL or enlarged uterine horn at 30-45 days Doppler Ultrasound, transrectal ultrasound Progesterone levels in blood and milk At 3 months, increase in blood flow in

uterine artery is felt as a buzz Ballottment- pressure on lower right

abdominal wall with fist or knee and lifts fetus, feel it kick back into place

Early pregnancy diagnosis 14-15 days Twin reduction <18 days Fetal sex determination 65 days Gestation period in bovine is 280-290

days with some breed variation

Parturition

Signs of impending parturition- Relaxation of tail head muscles- Relaxing /Lengthening of vulva- Waxing of teats- yellow tinged colostrum,

extended/excessive dripping may result in insufficient colostrum available for newborn

Stages of Labor

Stage 1 labor- may be interrupted several times without injury to fetusStage 2- duration one hour- Rupture of placental membranes, water

breaking, may look like urination- Vaginal exam is performed 5-10 minutes

after onset of stage 2 labor to assess fetal presentation, cervical dilation

Stage 3- placenta delivered

Normal parturition

Presentation of fetus- forelegs first ( breech birth, hindlegs first, is normal presentation in goats, swine and sheep)

Most cows and mares will lie down prior to expelling calf/foal, if traction is required for delivery, attendant pulls down- toward the dams hocks, not straight out, parallel with the spine

Allow neonate to rest with hindlegs still in vaginal canal if the umbilical cord is intact. Up to 1 liter of blood may be transferred from the placenta to offspring

Neonate should be standing, ambulatory and nursing within one hour after birth

Expulsion of placental/fetal membranes ( afterbirth) cleaning should occur within several hours of birth. Membranes that are not completely passed within 8-12 hours represent a medical emergency; retained placenta

Dystocia

Factors affecting risk of dystocia- Abnormal presentation- Multiple births- Heifer vs cow- Pelvic measurement- Nutritional status- obesity/malnutrition

Dystrocia correction

Repulsion then traction Pubic symphysiotomy- in first calf heifers, if

calfs head is larger than the pelvic canal the veterinarian can open and spread the suture between the pubic bones thus enlarging the pelvic canal diameter

Cesarean section Fetotomy- if fetus is dead, dismembered

and delivered in pieces. Note: care must be taken to avoid sharp bone pieces piercing/rupturing uterine wall

Post partum care of the dam

Examine vagina, vulva and perineal body for injury

Examine afterbirth for completeness Examine mammary glands, express

colostrum for evaluation Monitor abdominal discomfort, mm Monitor maternal behavior, interaction

with newborn

Post partum complications for the dam

Vaginal/uterine prolapse Obturator paralysis Milk fever/hypocalcemic tetany Rejection of offspring

Post partum care of neonate

Colostrum- Requirement – 1 liter per 100 lbs- Colostrum banking- dams will produce

more colostrum than needed. After neonate has consumed a sufficient amount, the rest may be milked out and frozen for storage for up to 1 year

- Colostrum quality- ( quality = immunoglobulin content)

a. subjective- stickiness, thickness (Note: color is not a reliable criteria for assessing quality)

b. Objective- specific gravity > 1.060- Gut closure- the neonatal intestinal tract has the transient capability to absorb large ( immunoglobulins) molecules intact. That capability is lost after 24 hours or the consumption of 32 ounces of material. Colostrum consumed after gut closure is of no benefit.

- behavior- strong suck reflex- Umbilicus- iodine ( foals apply every 12

hours until navel remains dry)- Meconium- feces that accumulates in the

colon during fetal development, can be rock hard and difficult to pass. If straining is observed, administer phosphate enemas until meconium is passed. ( colostrum has laxative)

Post partum emergencies of neonate

Distress, lack of vigor, cyanosis Aspiration of amniotic fluid- breech

birth/dystocia- hold foal/calf upside down to clear airway of fluid before initiating CPR

a. A- airway, establish patent airway firstb. B- breathing, dopram may be

administered to stimulate respirationc. C circulation- cardiac compressions,

resuscitation

Failure of Passive Transfer- absence or decreased levels of circulating IgG ( of maternal origin, neonate cannot produce its own IgG until 3-4 months of age)

a. IgG <200 mg/dl is complete failure b. IgG200-400 mg/dl- is partial failurec. IgG > 400 is adequate passive transfer

Mare origin failure of passive transfer- Loss prior to foaling ( leaking)- Poor quality ( low levels of

immunoglobulins in colostrum)- Failure to produce colostrum, neonates

born before reaching term

Foal origin failure of passive transfer- Inadequate colostrum- Gut closure Treatment - Administer colostrum or plasma orally if

FPT is diagnosed before gut closure- Administer plasma intravenously if FPT is

diagnosed after gut closure

Neonatal isoerythrolysis

Maternal antibodies in colostrum destroy foals RBC’s

- Does not occur in primiparous, first foal mares

- Symptoms: anemia, icterus, hemoglobinuria- Prevention: agglutination test prior to

allowing foal to nurse- Agglutination test- foals RBC’s mixed with

graded dilutions of colostrum, evaluated for agglutination

- TX: transfusion if HCT < 15%

Neonatal maladjustment syndrome

Dummy foal syndrome Suck reflex absent and may take 30+

days to resolve High risk foal-failure of passive transfer or

neonatal septicemia Guarded prognosis

Neonatal nutrition

Neonate should consume 10% of body weight per day in milk or milk replacer

Foals: typical nursing pattern of once per hour consuming 90 ml per feeding

Note: mare goes into heat 5-7 days post foaling. Hormones passed in milk result in diarrhea of foal ( foal heat diarrhea). This diarrhea rarely requires medical intervention and spontaneously resolves when mare goes out of heat.

Orphan animal/animals unable to nurse on dam

a. Bottle feeding- healthy animals with normal suck reflexb. Bucket feeding- Much easier than bottle feeding- Orphans should be trained to bucket asap

to minimize labor costs and decrease aberrant behavior associated with hand raised animals

- Tube feeding for foals lacking sucking reflex

- Esophageal feeder for calves/lambs/kids- Transfer of neonate to foster dam

Medical care of healthy animal

Deworming- typically begins at the same time as initial vaccination series

Vaccinations not performed until maternal antibody levels decrease

- Foals: 4 months- Calves: 6 months- Sheep/goats- 2 months- Pigs- 3 weeks

Social behavior1. Imprinting- Training to accept procedures that will be

performed later in life- Bonding with dam/other animals/humans

2. Provide companion if dam is unavailable, alternate species is acceptable