O Level Notes : Agriculture - Animal Health and Improvement

Breeding of animals is a nature's way of ensuring that the species continues to live from one generation to the next. In animal breeding the aim is to produce a regular supply of young animals which can later be sold for profit. However to get the best results, the farmer must ensure selection of best stock breeds.

The farmer should also be able to manage diseases and parasites in order to achieve good results. The control of parasites and diseases in livestock is of vital importance if animals are to grow and develop properly. Diseased stock is a problem on a farm and it is uneconomic to keep sick animals at a farm as it cost the farmer due to treatment costs. Many diseases can be prevented by dipping, vaccination and practicing hygiene. Diseases are mainly caused by internal and external parasites.


It is the science of multiplying animals through in breeding and or cross breeding. 

Importance of breeding

  • Increased multiplication of animals.
  • It improves animal growth rate.
  • It improves adaptability of animals to harsh climatic conditions.
  • Breeding improves fertility of the animals.
  • It improves productivity. Animal products like meat, milk, wool, hides and eggs will be of high quality and quantity.
  • Breeding improves animal resistance to diseases and parasites


Effects of environment on breeding

Environmental factors are those factors which an individual animal encounter from time of conception until death. The environmental factors causes phenotypic variation in animals that is, the general outlook or observable outward appearance of an individual. The environmental factors are not passed on from the parents to the offspring.


Environmental factors which affect the degree of expression of the genotype of an animal

  • Type of food
  • Diseases and parasites
  • Housing systems
  • Nutritional level
  • Local temperatures
  • Availability of water

Artificial selection of animals for breeding

Selection is the choosing of animals which will become the parents of the following generation. The main purpose of selection is to change gene frequency in a population so that genotypes produced are those that meet the requirement of the breeder. It involves allowance of some animals to be parents of the next generation whilst depriving others of the priviledge.

Factors to consider when selecting animals for breeding

  • Growth rate - animals with fast growth rate are selected because such animals have a good (FCR) Food Conversion Ratio.
  • Conformation - this refers to the physical structure of the animal.
  • Physical size - large boarded animals are selected for breeding.
  • Be observant and select animals without disabilities for breeding.
  • Consider animal records and select animals with good record such as high fertility, good calving or resistant to parasites and diseases.


Breeding methods

There are many methods used by farmers for breeding but however in this chapter we are going to discuss about inbreeding and cross breeding only.



In breeding is the mating of animals that are closely related to each other, that is the

mating of animals that have one or more ancestors in common. Inbreeding is common in rural areas and small scale farmers where breeding is not controlled. Inbreeding can be done by farmers deliberately when there are traits of economic importance to be maintained with in the herd. To be sure that the offspring born from selected mating will be satisfactory, the farmer must consider the inherited characteristics of the parents. An example of inbreeding is when a bull within the herd breed with its daughters and or young bulls in a herd breed with their mothers, sisters and grandmothers.


Advantages of inbreeding

  • It maintains uniformity with in the herd, a characteristic which is important to a farmer when included in competitions like agricultural shows.
  • Offspring are true to type.
  • Desired characteristics can be maintained with in the herd.


Disadvantages of inbreeding

  • Some offsprings might have disabilities.
  • Usually results in poor tolerance to diseases and parasites.
  • Lead to reduction in animal size (dwarfism).
  • Can cause poor fertility.
  • It is a reproductive performance reduction due to delayed puberty in both sex that is, reduced testicular size in males, reduced number of ova shade in females and increase in embryonic death.


Inbreed genetic crosses

It is important to state the dominant and the recessive trait controlling genes when doing genetic cross. The traits are represented by letters of the alphabet which are usually capital letters for the dominant gene and small letters for the recessive gene.

Example of inbreed genetic cross


Genes involved

T = dominant gene (disease resistant)

t  = recessive gene (prone to diseases)


Parental genotype     Tt (bull)              x     Tt (cow)

Bull's gametes                                                              cow's gamete


Tt                                                                                        T t 




Tt                            tt

Disease resistant

disease resistant

disease resistant    prone to diseases

The ratio of F1 generation is 3 : 1, thus 3 offsprings will be resistant to diseases and only 1 offspring will be prone to diseases


Cross breeding

Cross breeding is the practice whereby animals of different breeds of the same species are mated. The animals selected are pure breeds and the aim is to produce progeny with the best characteristics of both breeds. The progeny are known as cross breeds. For example black head Persian ewe crossed with Dorset Horn sheep, the offspring is a new breed called dorper.


Example of cross breeding


(Genotypes)          Dorset Horn(Ram)           Black head Persian(ewe)

(Pure breed)             B                  B                                       H                    H


BH                                        BH    BH              BH                             F1 Hybrids


All F1 generations are hybrids showing heterosis 

According to cross breeding of Dorsethorn Ram and black head Persian Ewe above, the observable characteristics of individuals in F1 are hybrids which are superior to both parents. The F1 will be another breed called Dorper which has a high growth rate and is able to survive in harsh conditions than the parents.


Advantages of cross breeding

  • New breed is formed
  • Cross breed animals may have higher or more suitable performance than any of the parental pure breed because of high breed vigour.
  • Offsprings produced are well adapted to the environment.
  • It improve genetic makeup of the genes
  • It brings about genetic variation with in the herd

Disadvantages of cross breeding

  • It requires displine and careful attention to the pedigree of the animals produced. In the absent of these, there is great danger of the programme generating poor quality animals.
  • The farmer has to purchase replacement stock at regular intervals for breeding making it expensive.
  • Purchase of new stock might bring in diseases at the farm

Difference between cross breeding and in breeding


Cross breeding

In breeding

Cross breeding is the mating of unrelated

animals of different breeds of the same species.

In breeding is the mating of closely related


In cross breeding new breed is formed

In breeding maintain the same breed

Offspring have hybrid vigour

No hybrid vigour

There is genetic variation

In breeding causes accumulation of undesirable traits



Genetic diagrams in test cross problems

Test cross involves the breeding of an individual with a phenotypically recessive

individual in order to determine the zygosity of the former by analyzing proportions of offspring. Phenotype zygosity can either be heterozygous or homozygous. Test crosses are used to test an individual's genotype by crossing it with an individual of a known genotype.


Example of test cross


Genes involved


B=dominant gene black

b= recessive gene white


(Parents) Bb







B                b





b  (Gametes)





BB                    Bb           Bb        bb    F1 =3:1

Black              Black            Black                                White


F1 generation shows two characters represented by genotypes BB and bb in the test cross observations. There is then the third type Bb. Phenotypically there are 2 gene colours Black and White with B being dominant to b. BB and Bb are black and bb is white, This shows that the parents were not true to type.

Animal health

Health is a state of optimal, physical, mental and social wellbeing, during which an

animal can behave normally, produce and work according to its genetic potential. A disease is an inability to perform physiological functions at normal levels as a result of infection by pathogens.

Pre disposing factors to ill health

  • Poor nutrition
  • Age
  • Heredity
  • Sudden change of temperature(chilling)
  • Previous diseases

The health of an animal is also affected by parasites which feeds on the livestock and transmit diseases. Parasites are divided into endo- parasites (internal) and ecto- parasite (external). A parasite is an organism that derives all its nourishment from another organism (host) while the host does not benefit from the association. Most parasites are host specific and have a particular organ in which they stay. These parasites cause mortalities to livestock, reduction in milk production, poor meat quality, and poor hide quality. They also causes expenditure due to purchasing of drugs.


Internal parasites

Internal parasites (endo-parasites) are organisms which live and feed while inside the body of a host. Examples are flatworms (Platyhelminthes), tapeworms (Cestodes) and round worms (Aschelinthes). Roundworms and tapeworms are usually found in the alimentary canal while liverflukes lives in the liver or bile ducts.

Identification of internal parasites



The common flukes are conical flukes and liver flukes. This chapter will give details on liverflukes.These are non-segmented, dorsally ventrally flattened and grey pink flukes. They are large leaf shaped flukes. The anterior end is usually prolonged into shape of a cone and the anterior sucker is located at the end of the cone. The ventral sucker is placed at the level of shoulders of the fluke.The internal organs are branched while the cuticle is covered in spines. They are hermaphrodite parasites which inhibits the bile ducts of cattle, sheep and goats.The lifecycle of the liverfluke depends on the intermediate host the water snail. Young flukes are eaten by cattle as they graze on vleis near ponds and dams. Once inside the animal, they penetrate the tissue until they rich the liver and they spent upto two months growing in the liver thereby causing damage. Once the flukes are mature, they enter the bile duct of the liver and remain there for many years.

Tape worms

These are thin, long narrow segmented worms. They can grow up to 5 metres in length.

The two most important species which attack livestock are Taenia Saginata (beef tapeworm) and Taenia Solium (pig tapeworm). The tapeworm consists of a head (scolex) with four suckers and several hooks with which it attaches itself to the intestinal walls. It also consists of many individual body segments called proglottides. Mature proglottides are at the rear while young ones are near the head. The mature segments break off one at a time and are passed out through faeces.

Round worms

Round worms are worms with a long round body which is non – segmented. They affect sheep goats and cattle. Their sizes vary and the females are larger than the males.

Wire worms

These are found in the folds of abomasum of the host animal. They are slender and red

from the blood that they suck.Asingle worm can suck 0.5ml of blood a day.



They have a hook at the end of the worm near the mouth and they are found in the first part of the small intestines.

  • Egg stage - eggs are passed out in faeces and they will hatch in to larva.
  • Larva stage - the larvae crawl up vegetation so that they will be ingested by grazing animals. Once ingested by the animal they enter into the abomasum where they get their nourishment until they become mature.
  • Adult: they mate and eggs are passed out in faeces.


Control of round worms

  • Regular dosing of animals with drugs such as systamex, ripercol and valbazen.
  • Rotate grazing with a considerable period between grazing. This practice causes many larvae to die before they can be consumed.
  • Correct stocking rate to reduce chances of infections.
  • Kraals should be regularly emptied of manure since they are infested with round worms and their eggs.
  • Suspected animals especially newly introduced animals should be isolated and treated for round worms.


External parasites

These are also referred to as ectoparasites. They are living organisms which attack the skin of the animals. They may live on and feed on the blood of host animal while they are outside the body of the host. Examples of external parasites are ticks, mites, lice, tsetse fly and mosquitoes.


Ticks affect animals in the following way;

  • They act as vectors (transmitters) of diseases such as red water, heart water and gull sickness in cattle.
  • They damage animal skins as a result of tick bites or mechanical damage as the animal tries to scratch itself due to irritation.
  • Wounds caused by ticks expose animals to secondary infections
  • They cause tick worry which results in reduced feed intake in animals hence poor growth rate


Types of ticks

There are two types of ticks namely soft ticks (Argasidae) and hard ticks (Ixodidae). Soft ticks have a soft dorsal upper cover whilst hard ticks have a hard shield like covering at the upper surface in males. Hard ticks cause more damage than soft ones. Unlike soft ticks which have several nymphal stages, there is only one nymphal stage in hard ticks.

Life cycle of ticks

The life cycle of ticks differs depending with the number of hosts required to complete the cycle. There are one host, two host and three host ticks. An example of a one host tick is a blue tick. It is a grayish- blue in colour with the males having yellowish legs. Their prediction  sites  are  the  dew  lap,  neck,  muzzle,  brisket  and  cheeks.  They  occur throughout the year with marked peaks in summer.

Description of the cycle

After mating the female tick feed on blood meal and gets engorged. The female drops off from the host to the soil and deposited about 2 500 eggs in humid hiding places and the eggs hatch in to tiny six-legged larvae.



The larvae climb on to vegetation and search for a host. The larvae find a host and feed on blood for 3 to 5 days. They molts in to a nymph. This is the removal of the outer soft skin which is replaced by a hard dorsal cover.



The nymph feed on blood on the same host for 3 to 6 days and they become fully engorged. They then enter a molting stage which last for 2 days and become an adult.



They develop sexually and mate. During mating the female feed on blood and become engorged then drop off the host to the ground and lay eggs.

Control of ticks

On host tick control

  • Use the correct strength of acaricides.
  • Spraying with sprayers and ensure that animals are thoroughly wetted. Applying tick grease under the tail and inside ears.
  • Dip the animals at correct intervals that is weekly in summer and fortnightly in winter.


Off host tick control

  • Burning of grass every 4 years to kill the ticks and eggs.
  • Rotational grazing so as to starve and kill the ticks.


Animal health act

The animal health act (1960) is the legislation through which department of veterinary endorses the law that control and prevents diseases in livestock. This act contains rules and regulations concerning the following activities;


  • Dipping of cattle for tick control

The animal health act states that animals should have a regularly dipping programme to kill ticks and prevent tick borne diseases. Animals should dip weekly in summer and fortnightly in winter with correct strength of acaricides so that ticks will not build resistance.


  • Quarantining of imported and exported animals

Animals will be isolated in a confined area before moving to their destination so that disease tests will be carried out. If there is any animal affected it will be treated and released soon after recovery.


  • Immunisation of animals

Immunisation is a process of injecting vaccines into an animal's body so that it will be able to build resistance. Vaccination is mostly done to prevent notifiable diseases such as foot and mouth, Newcastle, etc.


  • Restriction of animal movement

The animal health act does not allow movement of animals from one place to another without a permit from veterinary service department.


  • Controlling  notifiable diseases

Notifiable diseases are those diseases that should be reported to the responsible authority once suspected. This is because they can spread fast and cause economic loss of livestock. The veterinary service department will vaccinate health animals and kill the infected ones.


Vaccination is the administering of drugs for the purpose of boosting the immune system of the body against diseases. Vaccines are substances capable of producing antibodies in the blood stream to combat specific diseases, they are usually made up of killed disease organisms suspended in serum and are injected into the animal being treated. They gradually produce a reaction in the animal by causing it to produce antibodies which will control the disease. The farm animals should always be vaccinated against notifiable diseases


Some methods of disease control

The most important method to control diseases is hygiene. Farmers can make use of antibiotics, antiseptics, disinfections and serum.

  • Antibiotics: These are substances that are obtained from living organisms such as bacteria and they are usually in liquid form or tablets. When an animal has taken it into the body, they inhibit the growth and the spread of the disease causing organisms within its body thereby controlling the disease. An example of an antibiotic is a penicillin.
  • Antiseptics: These are drugs that are used to kill disease organisms. They are normally used externally on the wounds to prevent rotting and further growth of the disease causing organisms.
  • Disinfections: These chemicals are mostly used by farmers in animal houses in order to kill pathogens which will be either on housing walls, floors, feeding troughs and can also be used as foot bath.
  • Serum: This is the colourless liquid extracted from the blood of an animal which have naturally recovered from a certain disease and in which red and white blood cells would have been removed. Serum is used in the preparation of vaccines.


Immunity in livestock

Immunity can be either active or passive. Active immunity involves the production of antibodies by the body itself and the eventual development of memory cells. It will result into long term immunity. Passive immunity is acquired by administering the antibodies from another source. Passive immunity does not involve the development of memory cells therefore it is a short term type of immunity. Both active and passive immunity can be induced by natural or artificial means.


Examples of active immunity

Natural: the animal's body produces the antibodies in response to an infection by some pathogens.

Artificial: The body produces antibodies in response to the controlled exposure to the attenuated pathogen that is through vaccination.

Examples of Passive immunity

Natural: the animal receives antibodies from another organism. A good example is of

the foetus that gets colostrum or a new born baby through breast milk.

Artificial: the animal receives manufactured antibodies through external delivery. An example is of blood transfusion of monoclonal antibodies.

Here is what we have discussed in this topic

  • Importance of  animal  breeding  are  to  improve  productivity,  growth  rate, resistance to diseases and parasites.
  • Animals are selected basing on two methods namely artificial and natural selection.
  • Artificial selection is done basing on the appearance of outside features of the animal.
  • Animal parasites are classified into two groups, namely internal (endo- parasites which feed and live inside the body of an animal and external (ecto- parasites) which feed and live while outside the body of the animal.
  • Internal parasites can be controlled by dosing while external parasites can be controlled by dipping or spraying.
  • Some examples of internal parasites are liver flukes, conical flukes, tapeworms, wireworms and hook worms
  • Some examples of external parasites are ticks, flies, tsetsefly and mites
  • Livestock diseases can be controlled by- the use of vaccines, antibiotics, serum, antiseptic, disinfections quarantining, and dipping of animals
  • The animal  health  act  gives  methods  of  preventing  and  controlling  the occurrence of notifiable diseases


Definitions of Terms used in this topic

  • Host – an animal upon which a parasite is dependent.
  • Parasite- an organism which lives on or inside the host and depends on it for food.
  • Dosing- giving medicine through the mouth.
  • Vector- an organism which carries and transmits pathogens in another animal for example ticks.
  • Vaccinate- to inject a drugcontaining attenuated pathogens into the body. This allow the body to build up resistance to a more serious attack by the disease.
  • Heterosis (hybrid vigor) – the superiority of a hybrid over its parents