June 10, 2009

Farm Animal Reproduction - Basic Principles

Agriculture, farming, animal husbandry, reproduction, principles, puberty, breeding seasons, breeding cycles, signs of oestrus, pregnancy, future technological developments, glossary

Farm Animal Reproduction - Basic Principles

By Dr Clive Dalton

At a certain stage in an animal's life it reaches "sexual maturity". This is when it is capable of mating and reproducing. Size and liveweight are important factors affecting puberty, but breeding activity is controlled mainly by "physiological development" which is much more than just an increase in size or weight. It is how the body organs, especially the reproductive organs have developed.

Here are some average ages at which puberty occurs in farm animals, but realise that this can vary greatly, depending for example on how well the animals have been reared and fed.

Cattle 6 - 10 months
Sheep 7 - 8 months
Goat 7 - 9 months
Horse 1 - 2 years
Pig 4 - 5 months
Dog 6 - 9 months
Deer 14 - 18 months (varies with species)
Rabbit 5 months
Poultry 5 months

The Breeding Season and its Control
Under natural conditions animals don't breed when we want them to - they have a very definite "breeding season". This is strongly affected by the daylight and dark pattern - the scientific term "photoperiodicity" is used to describe this. The period when animals are not breeding is sometimes referred to as the "anoestrus" period.

Species vary, so for example the female sheep (ewe) starts her breeding season in the autumn as the days get shorter. The same occurs with the female goat (doe) and the female deer (hind in Red deer and doe in Fallow). Near the equator, sheep do not show this very seasonal breeding behaviour.

The males of these species will mate all the year round if a female in heat appears, but they show a greater desire to mate in the autumn. Male deer (Red deer stags and Fallow bucks) show a definite "rut" when they are very active and herd their mates into a group or harem and guard them. To some extent this behaviour is seen in male goat (buck or Billy), and in male sheep (ram) to a much smaller extent.

The female horse (mare) is the opposite to the above species. Her breeding season is stimulated by increasing daylight so she starts to breed in the spring a few days after giving birth. She is most sexually-active from November to January in New Zealand. The male horse (stallion) will mate all the year round if given the chance, but is also most sexually active in spring.

In the sow, her breeding cycle is stimulated by weaning the piglets. She comes on heat a few days after weaning which takes place at 6 or 8 weeks after birth. Sometimes taking the piglets from the sow for 24 hours is used to trigger breeding activity.

The cow is different again and will breed most of the year round but shows less breeding activity in the winter. Bulls will mate any time of the year.

This effect of daylight is clearly seen when animals are moved from one hemisphere to another. They alter their breeding seasons to suit the new light pattern. Near the equator with equal day and night, animals tend to be less seasonal in their breeding patterns.

Breeding seasons (Southern hemisphere)
  • Animals that breed in Autumn (Feb. - May) – sheep, goat, deer
  • Animals that breed in Spring (Sept. - Feb.) – horse
  • Animals that breed all year – cattle, pig, dog, rabbit, poultry
The Breeding cycle
Once the female animal has come out of the anoestrus period and starts its breeding season, it then shows a definite cycle when it will mate. We say that the animal has started to "cycle" and at set times in this cycle she will be willing to let a male mate with her.

Each species differs in their breeding cycle. Below is a summary giving an average value and a range around that average. Note the wide variation in some species.

Breeding cycles in farm animals
Cattle 21 days (range 18 - 24 days)
Sheep 17 days (14 - 21)
Goat 21 days (19 - 22)
Horse 21 days (19 - 40)
Pig 21 days (19 - 22)
Dog 6 months
Deer 18 days (14 - 22)

Heat or Oestrus
First note the spelling. "Oestrus" is the noun and "oestrous" is the adjective. Estrus is the American spelling for the same thing. We do not use it in New Zealand.

Heat or oestrus is the length of time that the female will stand to be mated or "served" by the male. There are a number of words used to describe oestrous, for example:
  • On heat (general use)
  • In oestrus (general use)
  • Bulling (in the cow)
  • Riding (in the cow)
  • Brimming (in the sow)
  • Hot on (in the mare)
  • Tupping (in the sheep)

Here is a summary of some average values for time on heat, and a range which you will find with animals in a real farm situation.

Oestrus lengths in farm animals

Cattle 14 hours (range 10 - 30 hours)
Sheep 24 hours (4 - 72 hours)
Goat 48 hours (2 - 3 days)
Horse 5 days (4 hours - 11 days)
Pig 24 hours (12 - 60 hours)
Dog 7 days (5 - 15 days)
Deer little known. A few hours

Signs of heat
Species vary greatly in their behaviour, and within a species there is great variation as well. So you have to be very observant and for example look for a combination of one or more signs of heat to confirm your diagnosis.

A female will not let a male mount and serve during the whole of the oestrous period. So you have to recognise the actual period of "standing oestrus" or standing heat when she will stand both to be mounted and served. It seems that nature has designed this behaviour to frustrate the male and concentrate the sperm in his reproductive tract. The main practical point to accept is that the mating pair may need time and impatience on the part of the stockperson will not do any good at all.

There are a number of signs to use such as:
  • Mucous discharge from the vulva.
  • Swelling of the vulva.
  • Bellowing and restless.
  • Seeking the company of other cattle (sexually active groups).
  • Riding and being ridden by other cows in a group of 3 - 5 others.
  • Mud on her flanks showing she has been ridden.
  • Withholding her milk - lowered production.
  • Walking around the paddock a lot.
  • Hair (or applied paint) rubbed off the tail bone and pins.
  • Standing to be mated by a bull.
Sheep and goat
There are very few signs of heat in the ewe, even when a ram is near. Ewes go and seek out the ram but do not mount each other like cows. The ram "hunt sniffs" through the flock and if a ewe on heat is approached by a ram, it will "tail fan" or waggle it's tail, stand still and turn its head to the rear to look at the ram.

The goat has similar behaviour to the sheep.

The sow vulva swells and in white pigs becomes pink. A sow on heat stands rock solid when pushed from behind. In AI the sow is straddled by the stockman and if she stands this is a sign of peak heat. Sows wander around a lot looking for a boar, often with ears pricked and making short high pitched grunt.

The mare is restless, will urinate a lot and stands with her hind legs splayed. If a stallion is near she "winks or flashes" her vulva. This is called "clitoral or vaginal winking" when she lifts her tail and exposes her vulva to a prospective male. She will call out to other horses and responds to the stallion's high pitched call.

There are very few signs of heat in deer other than the animal's response to the stag. Hinds will preen themselves and go and rub themselves and preen the stag. Courtship and mating is very rapid in deer.

The vulva of the bitch will become red and swollen and thick mucous and blood may be seen. She will urinate and the smell of this will excite the male. She may stand and then race around and play and tease the dog. He may solicit this behaviour too. If the male is slow to mount the bitch may mount him. Other females may mount the bitch in heat. In standing heat, the bitch stands with her back curved and tail held to the side.

Bull's Reproductive Organs
Learn to draw the male reproductive organs and label the different parts.
The bull's reproductive organs are present at birth and after puberty he is able to produce and deliver sufficient sperm to fertilise females.

Sperm or spermatozoa
These are the male contribution (called the male gamete) to the offspring and contain his genes which are carried on chromosomes in the nucleus of the cell. The normal healthy sperm is like a tadpole under the microscope and has a head with the nucleus inside, a body and a tail which moves rapidly to propel the sperm. Abnormal sperm under the microscope have bent tails.

The testicles
The male has two testicles held in the scrotum or purse. At puberty they drop through the inguinal canal (a hole in the body wall) so that they benefit from the lower temperature outside the body. This helps the sperm to remain fertile.

Bulls with large testicles have been shown to be more fertile and have greater libido than those with small testicles. Beef breeders now select for scrotal circumference in their bulls as a good indirect measure of fertility.

Testicles that do not descend through the inguinal canal in the body wall may cause problems. An animal with one or more undescended testicles is called a "rig" and some of them are fertile.

Squeezing the testicles back out of the scrotum and then removing the scrotum with a rubber ring makes the animal infertile as the testicles are kept at a higher temperature either back up through the inguinal canal of more likely under the skin along the belly of the animal. The animal still grows as fast as an "entire" male as it has the full benefit of its testosterone. It is called a "cryptorchid". But beware, there is always the chance that one of them could produce enough viable sperm to get a female pregnant as they certainly have the libido to try.

The testicles continually produce sperm which is then stored and matured in the coiled tube or "epididymis" at the base of the testicle.

Sperm then move up the narrow tube called the vas deferens into the urethra or tube down the centre of the bull's penis along which both sperm and urine from the bladder flows.

The testicles also play an important role in the male's sexually behaviour. There are cells in the testicles (sometimes referred to as testes) called "interstitial tissue" that produce a hormone called "testosterone". Its production is stimulated by another hormone called "pituitrin" produced in the pituitary gland below the brain.

Testosterone has four functions:
  • It gives the bull it's sex drive or "libido
  • It increases the growth rate of males
  • It develops male characteristics
  • It develops the accessory glands

Accessory glands
Near the base of the bladder there are a number of "accessory glands" which provide fluids that lubricate the sperm. These are called the:
  • The prostate gland (note the spelling)
  • The seminal vesicles
  • Cowper's gland
The mixture of sperm and accessory fluids is called "semen".

The penis
The bull's penis is a strong muscular organ. When the bull becomes sexually excited testosterone causes an increased blood flow to the penis and it goes from a "flaccid" state to the "erect" state. The arrector muscle pulls the bend out of it so that it protrudes from the sheath or "prepuce" ready for entry into the vagina and on "ejaculation" discharges the semen and fluids.

A single ejaculate of about 5-10 ml contains about four billion sperm. At current dilution rates of sperm this one ejaculate could inseminate 6 - 8,000 cows. Each insemination contains about 2 million sperm.

The end of the penis is called the "glans penis" and varies in different species because of the shape of the cervix in the female. The bull for example has an arrow head type glans while the ram has a worm-like structure on the end (villiform appendage). The boar has a corkscrew shape on his penis which locks into the sow's cervix with a left hand thread action. The stallion has a large chrysanthemum-like structure on its glans, while the dog has a bulbous gland on its penis which inflates after ejaculation and locks the dog inside the bitch for a while. He dismounts and remains "knotted". They should not be pulled apart of have water thrown over them!

Cow's Reproductive Organs
Learn to draw and label the reproductive system of the cow.

The vulva and vagina
The vulva are the outside lips of the vagina. The shape of the vulva with its extended lips project the urine off the body of the animal when it urinates.

The vagina leads into the main body of the reproductive tract and is where sperm from the male is deposited at mating. It is also where the entrance to the bladder via the urethra can be found.

At the end anterior end of the vagina is the cervix with the entrance called the os.

The cervix and uterus
The cervix is the neck or entrance to the uterus or womb. The actual entrance to the cervix is called the "os" (pronounced oss). The cervix is a muscular structure made up of many folds. This is a natural barrier to keep infection out of the uterus, and has to be penetrated by the pipette when the animal is artificially inseminated. With natural mating the sperm have to find their way through the cervix and many perish on the way.

The cervix of sheep is much more muscular than in the cow, and in the sow the boar has to be locked into the cervix before ejaculation occurs.

The uterus is made up of two "horns" and is where the fertilised ovum or "embryo" is attached. In animals that have more than one offspring or have litters (called multiparous), these can develop in either or both horns. In single-offspring species (called uniparous), the "foetus" grows in the main body of the uterus. In pigs for example, you will find a foetus along the length of each horn and the "runt" or small member of the litter is usually found in the top of the horn and is born last.

The Fallopian tubes
These are the narrow tubes down which the egg or "ovum" flows from the ovary and where fertilisation takes place. The ovum coming down meets the sperm coming up. Sometimes the term "oviduct" is given to this part of the system. At the top of the Fallopian tube is a cup-like structure called the "infundibulum" which catches the egg after it has been shed from the ovary.

The ovary
This organ produces the ova or eggs from the female. A young heifer calf for example has many hundreds of thousands of eggs in its ovaries ready to develop after puberty and which will mature and be produced over the animal's lifetime.
The ova are produced in waves

Hormonal Control in the Female
Successful reproduction in the female depends on a number of separate organs working together. These are:
  • the hypothalamus or lower part of the brain
  • the pituitary gland - a gland the size of a pea under the brain
  • the ovary
  • the uterus
Hormones are "chemical messengers". At puberty a hormone from the pituitary gland activates the ovary and a number of ova start to develop. This hormone is called "Follicle Stimulating Hormone" or FSH.

One ovum wins the race (in species that produce one offspring), and it matures into a follicle which looks like a red blister on the ovary surface. In animals that produce litters, both ovaries will carry these ripening follicles.

While the follicle is developing, it secretes a hormone into the bloodstream called "oestrogen". This causes the animal to show signs of heat or oestrus.

As well as causing oestrus, oestrogen stimulates the pituitary gland to produce a hormone called "Luteinising Hormone" or LH. This causes the follicle to rupture and the egg drops into the Fallopian tube to work its way down to meet the sperm when present. Fertilisation takes place in the top one third of the Fallopian tube and on about day 4, the fertilised egg or embryo is implanted into the wall of the uterus.

After the follicle bursts, the membrane that covered the follicle and the cells lining the follicle cavity produce a structure called the "Corpus Luteum" or CL. It is sometimes called the "yellow body" and has the important function of producing a hormone called "Progesterone". This is the "hormone of pregnancy". It stimulates the wall of the uterus to accept the fertilised egg and stops other follicles from maturing. This continues until the foetus can produce enough of its own progesterone to maintain the pregnancy.

If the female does not become pregnant, a hormone called "prostaglandin:" is produced by the uterus and this dissolves the Corpus Luteum so the whole cycle starts again.


The sperm meet the egg in the top third of the Fallopian tube. The rhythmic contraction of the uterus waft the sperm up the tubes and there are still millions of them present at this stage of their journey despite huge losses on the way. Sperm gather around the egg vibrating the shell, all trying to penetrate. This vibration alters the pH of the shell and assists penetration of the sperm. Only one succeeds and then the shell becomes impervious to the others which then die.

The seminal fluid from the accessory glands has an important role. Initially its role is to provide a fluid to help the sperm to flow. However, after a time it then changes its role and kills off the sperm. It seems as if Nature has intended the sperm to have a limited life and this varies greatly with species.

The sperm and egg are each single cells, and after joining start to multiply from two cells to four to eight, and so on. It is at these early stages before the eggs have attached that they can be flushed out of the Fallopian tubes and implanted into other animals.

This is called "Ovum Transfer" (OT) if they are collected and transplanted before fertilisation, or "Embryo Transfer" (ET) if collected and implanted after fertilisation.

They can also be split at this time or the contents called "germ plasm", which is a jelly-like substance, can be taken out and put into other egg shells.

In the cow implantation takes place on the same side of the uterus as the ovary from which the egg is shed. Attachment is caused by cells in the shell which form membranes that attach to the wall of the uterus. They serve to surround and protect the new embryo and start to form the "placenta" by which the embryo is fed from the dam.

In the cow this placenta forms into a bag around the calf which is seen at birth as the "afterbirth". The contact between the cow's blood supply and the calf's blood supply is through structures called "cotyledons" which work rather like Velcro and pull apart at birth. If they do not separate at birth the cow end up with a retained afterbirth which has to be treated to prevent infection of the uterus or "metritis".

In the horse and the pig the placenta does not have cotyledons but lines the entire uterus. This is called "diffuse" placentation in contrast to "cotyledenous" placentation. In the mare the placenta or afterbirth comes out as a large two-horned bag after the foal is born.

The dam not only feeds the calf through the placenta, but also removes all waste products as well. So the blood flow through the placenta is very important.

The first organs to develop in the calf or "foetus" are the brain and central nervous system, the heart and blood vessels. By the end of the first quarter of pregnancy most of the internal organs are formed and functioning in the foetus.

Pregnancy in different species
Cow 282 days (9 months + 3 days)
Sheep 140 - 150 days (5 months)
Goat 150 - 156 days
Horse 340 (325 - 347 days) (11 months & 11 days)
Pig 115 days (3 months, 3 weeks and 3 days)
Dog 58 - 63 days (9 weeks)
Deer 226 - 233 days. (Wapiti - 255 days)
Rabbit 31 days

Note the wide variation in some species.

During pregnancy the muscles of the uterus remain inactive. Shortly before birth the muscles in the cervix and the vagina relax in preparation for birth. The cartilage and ligaments in the pelvic area also become more flexible ready for the calf to pass through the pelvic cavity.

At birth, the muscles of the uterus undergo spasms or contractions to push the calf out towards the birth canal though the pelvis. In normal presentations this is head and feet first like a diver. Normally the placental link with the mother - the umbilical cord, remains intact until the calf hits the ground. Once born this is broken and the lungs inflate to allow the calf to breath on its own.

When calves are born backwards (breech presentations) the cord may break before the animal can breath through its lungs, and it can drown if the delivery is delayed.

The triggering of birth comes through a hormone from the foetus and not the mother.

Control of Reproduction
Good farm management requires control of animal reproduction. For example we want calving to coincide with the time when grass growth is at its peak, or we may want animals to give birth to suit particular markets. To improve animal performance we want to breed from the best and cull the worst. This demands control of reproduction.

There are a number of techniques used to influence the natural reproduction pattern. These include:
  • Castration
  • Vasectomy
  • Cryptorchids
  • Speying
  • Hormonal treatment - injections, implants under the skin, vaginal insertions (CIDRs)

CIDRs are used to get anoestrus animals to start cycling, and also to "synchronise" the breeding activity of those that have started to cycle so that they all come on heat together.

Future developments
Advances in reproductive technology are the way these genes will be multiplied and made commercially available. Here’s a brief description of some of these techniques which are at varying stages of commercial availability:

MOET: “Multiple ovulation and embryo transfer” - sometimes called “super-ovulation and embryo flushing”. The cow is stimulated to produce many more eggs (oocytes) than normal at ovulation, then after insemination the embryos are flushed from the uterus through the vagina. Very large numbers of embryos can be harvested but five good quality ones per flush is a realistic average. These can be implanted in to other cows treated with hormones to be at the correct stage of their cycle, or frozen for later use or sale.

TVR: “Trans-vaginal recovery” – also called “ovum pickup”. In TVR oocytes are taken directly from the cow’s ovaries and the operation can be performed on yearlings or cows soon after calving or even in early pregnancy. Oocytes can also be taken from cows immediately after death; this is called GR or “genetic rescue” and is an ideal way of exploiting the genes of former top-performing cows in the herd.

IVP: “In vitro production” is where embryos are grown in the laboratory and there are three stages to this. First is IVM or “in vitro maturation”, then IVF or “in vitro fertilisation” and lastly IVC or “in vitro culture” – the whole process taking eight days.

Sexed semen: This has been possible for some years (currently with 90% accuracy), but is not commercially available on a large scale yet. It’s ideal for an AI programme to breed females for replacements or males for beef.

Embryo genotyping: Here the genotype of the embryo can be checked before implantation. The aim is to avoid spreading defective genes and multiplying good genes – once they have been found. Currently there are only a few available but as the cow genome or genetic map is researched, more will be commercially available.

Embryo multiplication: This is the process of taking one embryo and dividing it up at the appropriate (early) stage to produce identical twins, triplets, quads – or more.

JIVET: “Juvenile in vitro embryo transfer”. This is where IVP is done on calves (one month old) and when perfected will be a powerful tool to reduce generation interval which is limited by the age of normal puberty. Currently results are not commercially satisfactory.

Clones: Clones are totally identical in their genetic makeup and have been produced from body cells as opposed to sperm or eggs. Dolly the sheep for example was produced from a cell from her mother’s udder. Cattle have been cloned and used commercially in AI to produce two bulls to meet a large demand for semen that one bull could not supply.

Short-gestation semen: Semen from bulls that have been selected to produce calves which are born less than the average 280 days gestation. The best bull currently available will shorten gestation on his calves by 8.4 days. These bulls are used by dairy farmers at the end of their AI programme to reduce calving spread.

Freeze-dried semen: When this is available commercially, it will make transport and delivery of semen easier.

AB: Artificial Breeding ( same as AI)
Abortion: premature expulsion of the foetus.
Accessory fluids: fluids produced by glands to help sperm to flow.
Accessory glands: glands that produce accessory fluids.
Afterbirth: the membranes (placenta) that have surrounded the developing foetus and attaching it to the dam.
Amniotic fluid:
the protective fluid around the foetus.
Anoestrus: the non-cycling period when oestrus is not shown.
Artificial vagina or AV: device a male serves into to for semen collection.
AI or Artificial insemination: placing sperm inside the female tract with a pipette.
Barren: failing to reproduce or incapable of reproducing.
Bearing: protruding or collapsed vagina.
Birth rank: the number born eg singles, twins, triplets, etc.
Breeding crate: a box designed to take the weight of a heavy male (eg boar) when serving a smaller female.
Bulling: see oestrus.
Buller: a nymphomaniac cow.
Amniotic fluid: the fluid around the foetus.
Castration: removal of the testicles of a male.
Cervix: the opening or neck of the uterus.
CIDR: a device in the female vagina to control breeding by slow release of hormones.
Colostrum: the first milk of the dam rich in antibodies.
Conception: fertilisation of an egg by a sperm.
Conception Rate (CR): percentage of females that do not return to oestrus, or are diagnosed pregnant.
Copulation: the act of mating.
Corpus Luteum: the structure which develops from the follicle after the egg is shed. May be called the "yellow body". Plural is "Corpora Lutea.
Corticosteriods: hormones produced from the adrenal glands and used to induce parturition or birth.
Cotyledon: the structure by which the foetal and maternal placenta are joined in the cow.
Cryptorchid: a male made infertile by pushing the testicles up into the body cavity and removing the scrotum.
Cycling: same as oestrus.
Chin ball harness: a device fitted to a bull to leave an ink mark on the mounted cow.
Dry: a animal that has not reproduced, or has finished lactating
Dystocia: birth difficulty.
Egg: same as ovum.
Ejaculate: ejecting the sperm from the penis. Or what is collected from this action and made up of sperm and seminal fluid.
Electroejaculation: collecting semen from a male using electrical stimulation.
Embryo: the early stage of development of the young in the uterus or shell
Embryo Transfer (ET): transferring embryos from one female to another.
Endoscope: same as a laproscope.
Entire: an uncastrated male.
Fecundity: a measure of the number of offspring born or reared.
Fertility: a measure of the female to conceive and produce offspring, or of the male to fertilise the female.
Fertilisation: the act of male sperm meeting female ovum and causing pregnancy.
Flushing: washing ova or embryos from the female's reproductive tract.
Flushing: in sheep feeding ewes well 2-3 weeks before joining with ram to increase the eggs shed and hence lambs born.
Foetus: the unborn animal in the womb.
Follicle: the structure in the ovary where an ovum matures.
Follicle Stimulating Hormone (FSH): hormone produced by the pituitary gland which controls ovulation in females and sperm production in males.
Fostering: making a mother accept an offspring from another dam, or giving an offspring to another dam to rear.
Freemartin: in cattle, a female born twin to a male is usually infertile.
Gamete: a reproductive cell (sperm or ovum).
Gestation: the time of pregnancy between conception and birth.
Glans: the structure on the end of the male's penis.
Gonads: a general term for the reproductive glands (ovaries & testicles)
Gonadotrophins: hormones from the pituitary gland that control the reproductive system.
Heat: the period when the animal shows willingness to be mated.
Hermaphrodite: a bisexual animal that has both male and female sexual organs.
Hormone: a "chemical messenger". Secretions from special glands that circulate in the bloodstream and affects different body functions.
Induction: a technique to cause early onset of birth buy using hormones.
In utero: a term which means in the uterus.
In vitro: means outside the body.
In vitro fertilisation (IVF): fertilisation in a test tube.
Joining: putting a male with a female animal for mating.
Laparoscope: a telescope for examining inside an animal's body through a small incision.
Laparoscopy: the examination done with a laparoscope.
Luteinising Hormone (LH): hormone from the pituitary which controls ovulation in females and testosterone production in males.
Libido: sex drive or urge to mate.
Mating: the act of mating. Animals may be joined but not mate.
Mating harness: a device fitted to males to colour mark females after mating.
Mortality: a measure of offspring born dead or died soon after birth.
Mothering: same as fostering.
Mothering ability: the ability of a dam to look after its young.
Mounting: one animal jumping up on another in an attempt to mate.
Multiparous: a dam that has many offspring or had many pregnancies.
Non parous: a female which has not given birth.
Nymphomaniac: female in continuous oestrus
Oestrogens: female steroid hormones secreted by growing ovarian follicles and which are concerned with oestrus.
Oestrus: period when the animal will stand to be mated.
Oestrous (adjective): same as oestrus.
On-the-drop: female about to give birth.
Out-of-season breeding: breeding animals outside their normal season.
Ovary: the female organ that produces the ova or eggs.
Ovulate: the act of shedding the egg or ovulation.
Ovulation rate: measured by inspecting the ovary and counting the corpora lutea.
Ovum: a single egg. Plural is ova.
Ovum Transfer (OT): collecting eggs from the female and putting them into other females.
Parity: how many pregnancies and animal has had.
Parous: a dam which has had offspring.
Parturition: same as birth.
Pellet: a small lump of frozen semen.
Perinatal mortality: mortality of young around birth.
Pheromone: chemical secreted by one animal that influences the sexual behaviour of another.
Pituitary gland: gland at the base of the brain which secretes hormones that control functions like reproduction and milking.
Placenta: the organ which attaches the offspring to its dam and through which it is fed.
Pregnant Mare Serum Gonadotrophin (PSMG): a hormone used in reproduction control to stimulate ovulation.
Pregnancy diagnosis (PD): finding out which animals are pregnant by hand palpation or using an electronic instrument.
Post-calving interval: the time between calving and first heat.
Premature: an animal born before its full term.
Prepuce: the sheath of skin around the protracted (withdrawn) penis.
Progesterone: a hormone produced by the Corpus Luteum which stimulates the uterus to accept the embryo and then maintains pregnancy.
Prolapse: eversion (turning inside out) or the vagina, uterus or rectum.
Prostaglandin: hormone produced by the uterus and used in reproduction control.
Puberty: the stage when the animal reaches sexual maturity.
Reproductive wastage: loss of eggs or embryos between mating and birth.
Returns-to-service: females that do not become pregnant and continue to cycle.
Riding: same as mounting.
Rig: an animal with one or both undescended testicles.
Season: "in season" is the same as "on heat"
Semen: the male reproductive cells made up of spermatozoa and accessory fluids.
Service: the act of the male mating the female.
Service interval: the time between services received by a female.
Sheath: another name for the prepuce, or the plastic cover for the pistolette used in AI.
Synchronisation: getting animals to show oestrus all at the same time using hormones.
Sperm or spermatozoa: the male sex cells or gametes.
Speying: surgical removal of the ovaries to prevent pregnancy. The Fallopian tubes many also be tied to prevent sperm meeting ova.
Springing: showing signs of birth such as udder development.
Straw: the fine plastic tube semen is packed in for AI.
Super ovulation: stimulating the female to produce larger than normal numbers of ova.
Tail painting: Putting paint on the tail head of cows which is then rubbed off or scuffed when mounted by other cows and denotes oestrus.
Teaser female: female with ovaries removed and used to stimulate males.
Teaser male: a vasectomised male.
Testicle: the male organ where sperm are produced.
Testes: same as testicles.
Testosterone: hormone produced by cells in the testicle.
Tubal ligation: tying the Fallopian tubes as in speying.
Uterus: the female organ in which the calf grows.
Vagina: anterior part of female reproductive tract.
Vulva: the outside lips of the vagina.
Yellow body: same as Corpus Luteum.

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