GROWTH and DEVELOPMENT

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GROWTH and DEVELOPMENT

• AGRICULTURAL SCIENCE
• Animal Science

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• 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
• Prenatal involves Embryonic and Foetal growth.
• Postnatal involves Puberty and Maturity.

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• PRENATAL GROWTH Factors affecting size at
  birth
• Number of young born.
• Size of the dam.
• Age of the dam.
• Sex of the litter members.
• Level of nutrition.

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• POSTNATAL GROWTH Factors affecting growth
• Size of the animal at birth.
• Sex of the animal.
• Breed
• Environment
• Genetics
• Nutrition

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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.

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• They are small implants given in the ear which
  slowly dissolve and release a hormone into the
  bloodstream.
• HGPs 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.

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• Delay fat composition.
• Do not improve meat quality.
• Repeat usage has shown a reduction in meat
  tenderness and marbling.

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BREEDING SYSTEMS

• Random
• Animals are allowed to mate at will.
• A large genetic pool.
• Produces great variation.
• Results are unpredictable.

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• 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.

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• 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).

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Diseases of Livestock

• The affects of disease
• Death
• Weakening and weight loss.
• Stunted growth.
• Lower production.
• Infertility resulting in fewer offspring.
• Reduced sale price.

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Infection and Disease

• Infection by an organism depends on
• A source of the pathogen.
• Transferral of the pathogen.
• Invasion of the host overcoming the hosts
  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.

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Disease Control

• 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 1980s.

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• 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.

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• 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.