Body Systems
Session 6 - The Reproductive System of Farm Animals
This resource is suitable to support Level 2 Agriculture courses.
The Male Reproductive System
The male reproductive system produces sperm which fertilise the
ova (eggs) in the female so that embryos are produced.
Hormones are produced which affect the animals’ behaviour and
lead to the development of secondary sexual characteristics
(such as the development of strong shoulders, head and neck).
Structure of the Male Reproductive System
The Functions of the Reproductive Organ
Testes/Testicles:
Produce immature sperm.
Produce male hormones.
Scrotal sac:
This is the skin surrounding the testes.
Epididymis:
Very long narrow tubes in which the sperm develop and mature.
The Functions of the Reproductive Organ
Spermatic cord:
This is the blood and nerve supply to the testicles.
Vas deferens:
This transports the sperm from the epididymis to the urethra. Fluid
from accessory sex glands is added to the sperm and this produces
semen.
Accessory glands:
Produce fluid to transport and provide nutrients for the sperm.
Penis:
This is the male organ used for mating; it is used to deposit the
semen into the female’s vagina.
Castration
Male calves and lambs that are kept for meat may be castrated
when they are young to prevent them from developing secondary
sexual characteristics.
Castration can also make management easier as they will not be
able to mate with female livestock on the farm, may be less
aggressive, safer and easier to handle. However growth rate may
be reduced.
Piglet castration
Piglets may also be castrated, however, the practice is less
common than in the past.
Castration can prevent boar taint (meat from entire males having
an unpleasant taste), but many pigs are slaughtered at a
sufficiently early age for it not to be a problem.
There are strict regulations concerning the castration of
livestock
Vasectomies
Entire males produce pheromones (chemicals) that send messages to
females which can stimulate female hormone production.
Rams which have been vasectomised are called teasers; that is they
have had the vas deferens cut so that the sperm which is produced
will not be able to reach the penis.
Teasers will produce pheromones and behave like entires, however
they will be infertile.
They are used to synchronise the breeding season of female
livestock.
Fertility
Fertile bulls and rams will produce semen which contains large
amounts of healthy active sperm.
For the animals to be fertile the sperm produced must be mature.
Testicles are placed in the scrotal sac outside the body cavity
to produce and store sperm at a lower temperature.
Sperm is easily damaged if it is too warm.
Ram Fertility
Rams are usually given a physical inspection well before the
breeding season to check for any abnormalities which could reduce
their fertility.
There is an infertility rate of approximately 10% in mature rams.
Problems Affecting Ram Fertility
Infections in the body e.g lameness can reduce fertility by
increasing body temperature and reducing the viability of sperm.
Infections also reduce physical activity and even though not
directly affecting the reproductive system, it creates a reduced
willingness to serve females which will reduce flock fertility.
Sperm Sample
Samples of sperm can be collected and studied under a microscope
to assess sperm quality.
Common faults include lack of movement, deformities and damaged
tails.
The Female Reproductive System
The female will produce the ova (eggs) that can be fertilized to
produce embryos.
The embryos will be nourished in the uterus until parturition
(birth).
The female reproductive system will produce a range of hormones that
will control the maturing and release of ova; they will also make
the female receptive to the male so that she will stand to be mated.
The Female Reproductive System
The Functions of the Reproductive Organs
Ovary:
These contain ova that develop inside follicles. The ova only
develop a few at a time (the number varies with the species of
animal and its condition). It is where female hormones are
produced.
Fallopian tubes:
These collect the ova when they are released (ovulation) and
carry them to the uterus. Fertilization takes place between the
ovum and the sperm in the Fallopian tubes. The fertilized egg
the travels to the uterus.
The Functions of the Reproductive Organs
Uterus:
The uterus or womb is where the embryo develops. During
pregnancy the embryos will attach to the uterus and nourishment
will be transferred from the mother through the placenta.
Cervix:
A thick band of muscle that closes the neck of the uterus. It
allows semen to enter when the animal is on heat and opens for
her to give birth. It prevents infections entering the uterus
and keeps the developing foetus inside the uterus.
The Functions of the Reproductive Organs
Vagina:
Holds the penis during mating so that the sperm will be
deposited in the right place.
Vulva:
The external opening of the female reproductive tract.
Puberty
Puberty is the stage in an animal’s life when it becomes
sexually active and is capable of reproducing.
The age will vary between individuals and the following factors
will influence the timing of puberty.
What Influences the Timing of Puberty?
Breed.
Body weight and nutrition (this may be far more important than age,
particularly for females).
Effect of changing day length (decreasing day length will trigger
breeding activity in sheep and an increasing day length will trigger
breeding activity in horses and birds).
Environmental factors e.g. the presence of males.
The Reproductive Cycles
The stage during the reproductive cycle when a female will stand
to be mated is known as oestrus.
During the breeding season mature females that are not pregnant
will have an oestrus cycle at regular intervals.
Length and Duration of Oestrus in Cows, Ewes and Sows
Table shows length and duration of oestrus in cattle, sheep and
pigs. Adapted from Black’s Veterinary Dictionary.
Seasonal and Non-seasonal Breeding Cycles
Cattle and pigs kept in agricultural systems breed throughout the
year.
Sheep are seasonal breeders; the breeding season will start in the
autumn, in general the lowland breeds will start to cycle earlier in
the year than the hill and upland breeds.
Seasonal and Non-seasonal Breeding Cycles
The Oestrus Cycle
The oestrous cycle is controlled by female hormones.
These will coordinate the maturing and release of the ova with the
animals’ reproductive behaviour.
If the ova is fertilized the hormones will maintain the pregnancy.
Female Reproductive Hormones
Follicle Stimulating Hormone (FSH):
This is produced by the pituitary gland and it stimulates the ova to
mature in the follicle.
Luteinising hormone (LH):
Makes the follicle burst and release the ovum.
Female Reproductive Hormones
Oestrogen:
Makes the animal show the signs of heat.
Progesterone:
Blocks FSH and stops the animal ovulating, if an ovum (egg) is
fertilized then the progesterone level will stay high throughout
pregnancy.
Prostaglandins:
If the egg is not fertilized then the uterus will produce
prostaglandins and the cycle will be repeated.
Diagram of the Oestrus Cycle Showing the Hormone Levels
Pregnancy
If the ova are fertilized the cell will rapidly divide and multiply.
The embryo will implant into the wall of the uterus to gain
nourishment from the dam.
If the dam is under stress e.g. not getting enough feed, then the
embryo may fail to implant.
Gestation Periods - Length of Pregnancy
What Can Affect the Gestation Length?
The length of the gestation period is affected by the number of
offspring, breed and sex of embryo.
In general twins have a shorter gestation length than singles,
beef breeds longer than dairy breeds and male feti have a longer
gestation length than females.
