Transcript GROWTH and DEVELOPMENT

GROWTH and
DEVELOPMENT
AGRICULTURAL SCIENCE
Animal Science
GROWTH – is the increase in size and
weight as the animal gets older.
 DEVELOPMENT – is the change in
proportion of various parts of the body.
Can also be described as the stages of
growth of an animal.
STAGES OF GROWTH:
1. Prenatal – involves Embryonic and Foetal
growth.
2. Postnatal – involves Puberty and Maturity.

PRENATAL GROWTH – Factors affecting
size at birth:
1. Number of young born.
2. Size of the dam.
3. Age of the dam.
4. Sex of the litter members.
5. Level of nutrition.
POSTNATAL GROWTH – Factors affecting
growth:
1. Size of the animal at birth.
2. Sex of the animal.
3. Breed
4. Environment
5. Genetics
6. Nutrition
Hormone Growth
Promotants.
 A group of veterinary drugs that mimic the
hormones that influence the growth of cattle.
 They may be natural or synthetic in
compound.
 They improve the feed conversion rate of
cattle.
 Are used to increase growth rates and
muscle development.
 They are small implants given in the ear
which slowly dissolve and release a
hormone into the bloodstream.
 HGP’s can contain female hormones –
oestradiol or progesterone.
 Also contain male hormones – testosterone
or trenbolone acetate.
 Sometimes they will be a combination.
 Implants containing trenbolone acetate are
generally referred to as ‘aggressive’
implants because they increase growth
rates.
 Delay fat composition.
 Do not improve meat quality.
 Repeat usage has shown a reduction in
meat tenderness and marbling.
BREEDING SYSTEMS
Random:
 Animals are allowed to mate at will.
 A large genetic pool.
 Produces great variation.
 Results are unpredictable.
Inbreeding:
 Mating of close relatives – father/daughter,
mother/son, full and half siblings.
 Increased uniformity.
 Greater chance of genetic diseases –
homozygous recessives.
Linebreeding:
 Bloodlines based on a single common
ancestor (stud breeders).
 Useful in passing on the genes of an
outstanding animal over several
generations.
Outbreeding:
 Mating of unrelated animals of the same
breed.
 Most commonly used system for
commercial sheep and cattle herds.
Crossbreeding:
 Mating of unrelated animals of different
breeds.
 Offspring are more productive than either of
the parents (heterosis/hybrid vigour).
Diseases of Livestock
The affects of disease:
1. Death
2. Weakening and weight loss.
3. Stunted growth.
4. Lower production.
5. Infertility resulting in fewer offspring.
6. Reduced sale price.
Infection and Disease
Infection by an organism depends on:
 A source of the pathogen.
 Transferral of the pathogen.
 Invasion of the host – overcoming the host’s
barriers to infection.
 Establishment of the pathogen within the
host.
The extent of damage will depend on the
ability of the organism to grow or produce
toxins.
Disease Control
1. Eradication involves the complete removal
of the disease by a process of testing and
slaughter.
 Very expensive
 Difficult to achieve 100% success.
 Used to eliminate brucellosis and
tuberculosis from Australian cattle herds in
the 1980’s.
2. Vaccination stimulates the body to
produce antibodies against diseasecausing organisms.
 Vaccination is a cheap and effective
method of preventing disease.
 Used for both bacterial and viral diseases.
 Vaccines contain either – dead organisms,
live organisms (weakened), toxins.
 Examples contain 7 in 1 for cattle –
protects against 5 clostridial diseases and
2 types of leptospirosis.
3. Chemical control – is used for internal and
external parasites.
 Quick and effective.
 Reasonably cheap – debateable.
 Disadvantage is that parasites and
pathogens are continually developing
resistance.
 Many chemicals are toxic to humans.
 Chemical residues can remain in the meat
and milk.