GROWTH and GROWTH and DEVELOPMENTDEVELOPMENTAGRICULTURAL SCIENCEAGRICULTURAL SCIENCE

Animal ScienceAnimal Science

GROWTH – is the increase in size and GROWTH – is the increase in size and weight as the animal gets older.weight as the animal gets older.

DEVELOPMENT – is the change in DEVELOPMENT – is the change in proportion of various parts of the body. proportion of various parts of the body. Can also be described as the stages of Can also be described as the stages of growth of an animal.growth of an animal.

STAGES OF GROWTH:STAGES OF GROWTH:

1.1. Prenatal – involves Embryonic and Foetal Prenatal – involves Embryonic and Foetal growth.growth.

2.2. Postnatal – involves Puberty and Maturity.Postnatal – involves Puberty and Maturity.

PRENATAL GROWTH – Factors affecting PRENATAL GROWTH – Factors affecting size at birth:size at birth:

1.1. Number of young born.Number of young born.

2.2. Size of the dam.Size of the dam.

3.3. Age of the dam.Age of the dam.

4.4. Sex of the litter members.Sex of the litter members.

5.5. Level of nutrition.Level of nutrition.

POSTNATAL GROWTH – Factors affecting POSTNATAL GROWTH – Factors affecting growth:growth:

1.1. Size of the animal at birth.Size of the animal at birth.

2.2. Sex of the animal.Sex of the animal.

3.3. Breed Breed

4.4. EnvironmentEnvironment

5.5. GeneticsGenetics

6.6. NutritionNutrition

Hormone Growth Hormone Growth Promotants.Promotants.

A group of veterinary drugs that mimic the A group of veterinary drugs that mimic the hormones that influence the growth of cattle.hormones that influence the growth of cattle.

They may be natural or synthetic in They may be natural or synthetic in compound.compound.

They improve the feed conversion rate of They improve the feed conversion rate of cattle.cattle.

Are used to increase growth rates and Are used to increase growth rates and muscle development.muscle development.

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

HGP’s can contain female hormones – HGP’s can contain female hormones – oestradiol or progesterone.oestradiol or progesterone.

Also contain male hormones – testosterone Also contain male hormones – testosterone or trenbolone acetate.or trenbolone acetate.

Sometimes they will be a combination.Sometimes they will be a combination. Implants containing trenbolone acetate are Implants containing trenbolone acetate are

generally referred to as ‘aggressive’ generally referred to as ‘aggressive’ implants because they increase growth implants because they increase growth rates.rates.

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

meat tenderness and marbling.meat tenderness and marbling.

BREEDING SYSTEMSBREEDING SYSTEMSRandom:Random: Animals are allowed to mate at will.Animals are allowed to mate at will. A large genetic pool.A large genetic pool. Produces great variation.Produces great variation. Results are unpredictable.Results are unpredictable.

Inbreeding:Inbreeding: Mating of close relatives – father/daughter, Mating of close relatives – father/daughter,

mother/son, full and half siblings.mother/son, full and half siblings. Increased uniformity.Increased uniformity. Greater chance of genetic diseases – Greater chance of genetic diseases –

homozygous recessives.homozygous recessives.Linebreeding:Linebreeding: Bloodlines based on a single common Bloodlines based on a single common

ancestor (stud breeders).ancestor (stud breeders). Useful in passing on the genes of an Useful in passing on the genes of an

outstanding animal over several outstanding animal over several generations.generations.

Outbreeding:Outbreeding: Mating of unrelated animals of the same Mating of unrelated animals of the same

breed.breed. Most commonly used system for Most commonly used system for

commercial sheep and cattle herds.commercial sheep and cattle herds.

Crossbreeding:Crossbreeding: Mating of unrelated animals of different Mating of unrelated animals of different

breeds.breeds. Offspring are more productive than either of Offspring are more productive than either of

the parents (heterosis/hybrid vigour).the parents (heterosis/hybrid vigour).

Diseases of LivestockDiseases of Livestock

The affects of disease:The affects of disease:

1.1. DeathDeath

2.2. Weakening and weight loss.Weakening and weight loss.

3.3. Stunted growth.Stunted growth.

4.4. Lower production.Lower production.

5.5. Infertility resulting in fewer offspring.Infertility resulting in fewer offspring.

6.6. Reduced sale price.Reduced sale price.

Infection and DiseaseInfection and DiseaseInfection by an organism depends on:Infection by an organism depends on: A source of the pathogen.A source of the pathogen. Transferral of the pathogen.Transferral of the pathogen. Invasion of the host – overcoming the host’s Invasion of the host – overcoming the host’s

barriers to infection.barriers to infection. Establishment of the pathogen within the Establishment of the pathogen within the

host.host.The extent of damage will depend on the The extent of damage will depend on the

ability of the organism to grow or produce ability of the organism to grow or produce toxins.toxins.

Disease ControlDisease Control

1.1. Eradication involves the complete removal Eradication involves the complete removal of the disease by a process of testing and of the disease by a process of testing and slaughter.slaughter.

Very expensiveVery expensive Difficult to achieve 100% success.Difficult to achieve 100% success. Used to eliminate brucellosis and Used to eliminate brucellosis and

tuberculosis from Australian cattle herds in tuberculosis from Australian cattle herds in the 1980’s. the 1980’s.

2.2. Vaccination stimulates the body to produce Vaccination stimulates the body to produce antibodies against disease-causing antibodies against disease-causing organisms.organisms.

Vaccination is a cheap and effective Vaccination is a cheap and effective method of preventing disease.method of preventing disease.

Used for both bacterial and viral diseases.Used for both bacterial and viral diseases. Vaccines contain either – dead organisms, Vaccines contain either – dead organisms,

live organisms (weakened), toxins.live organisms (weakened), toxins. Examples contain 7 in 1 for cattle – Examples contain 7 in 1 for cattle –

protects against 5 clostridial diseases and protects against 5 clostridial diseases and 2 types of leptospirosis.2 types of leptospirosis.

3.3. Chemical control – is used for internal and Chemical control – is used for internal and external parasites.external parasites.

Quick and effective.Quick and effective. Reasonably cheap – debateable.Reasonably cheap – debateable. Disadvantage is that parasites and Disadvantage is that parasites and

pathogens are continually developing pathogens are continually developing resistance.resistance.

Many chemicals are toxic to humans.Many chemicals are toxic to humans. Chemical residues can remain in the meat Chemical residues can remain in the meat

and milk.and milk.