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GROWTH and DEVELOPMENT

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					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 disease-
   causing 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.

				
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posted:4/3/2014
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