Livestock Selection and Breeding
Introduction
The breeding of animals is under human control, and the breeders decide which individuals shall produce the next generation. The breeder makes a choice.
The breeding of animals is based upon the fact that certain qualities are genetic ,hence valuable qualities are passed on from parents to off -springs. The qualities can be maintained or improved in the next generation.
The performance of an animal is influenced by two major factors;
- Genetic potential
- The environment, which includes:
Feeding,Health, care and the ecological conditions.
The genetic potential of an animal is inherited from its parents.
In selection and breeding animals with superior characteristics are selected and allowed to mate.
In the process they transmit the superior characteristics to their offspring.
When this is done over a long period of time, it results in livestock improvement.
Reproduction and Reproductive Systems
Reproduction is the process by which off-springs are produced. All farm animals multiply by means of sexual reproduction.
It begins with fertilization which is the fusion of male and female gametes to form a zygote. Fertilization takes place internally in the body of the female. The embryo(zygote) formed develops inside body of mother, fed and protected until end of gestation period.
In poultry, the process is different in that eggs are fertilized internally but laid and development of the chick takes place outside during incubation.
In both male and female, certain organs are specialized for the process of reproduction.
Some of these organs secret fluids which are necessary for the movement and survival of the gametes(reproductive cells.)
Reproduction in Cattle
1. Male Reproductive System (Bull)
The male reproductive organs produce the male gametes,the spermatozoans.
The reproductive system(bull) iscompsed of the following parts;
i). Testes
ii). Epididymis
iii). Sperm ducts
iv). Accessory glands(Seminal vesicles and prostrate glands)
v). Penis
The testis:
- There are two testes hanging loosely between hind legs.
Enclosed by loose skin (scrotum)scrotum regulate temperature of testis for optimum production of sperms.
- Produce spermatozoa(sperms)which are stored in coiled tube called epididymis.
Epididymis: Storage of spermatozoa.
Sperm ducts:
- Conveys sperm from the testis and urine through the penis.
- sphincter muscles contract to allow each to pass separetly.
Seminal vesicles produce fluid called semen. Semen carries sperms out of penis in fluid form.
Semen contains nutrients to the spermatozoan.
Prostate gland -produce fluid that neutralize the acidic effects of urine in the urethra preventing death of sperms.
Accessory glands: Include seminal vesicles cowpers gland and prostate gland. Urethra: Conveys urine and semen.One sperm fertlizes ovum
Penis:
- Surrounded by a sheath which is an extension of skin.
- It introduces sperms into the vagina of a cow through the vulva during mating.
- It is a copulatory organ, also used for urination.
2. The Female Reproductive System(Cow)
the reproductive systemm of a cow is composed of;
i). Ovaries
ii). Fallopian tubes
iii). Vagina
iv). Vulva
v). Uterus
Ovaries and fallopian tubes(oviduct)
Two ovaries located in abdomen, left and right. Produce ova/eggs and hormones which control sexual cycle. Oestrogen produced by graafian follicle inside ovary induces oestrus i.e. Heat period so that the cow shows signs of heat. The hormone oestrogen is produced under the influence of other hormone called the Follicle stimulating hormone.
After every 21 days the ovary releases a mature ovum and the cow comes on heat. The ovum travels through the fallopian tubes to the uterus.
The release and movement of the ovum down to the uterus is called ovulation. If mating is done at this time, fertilization will take place.
The fertilized egg implants itself onto the endometrium(walls of uterus)and develops into foetus.
Fallopian tubes:
Fertilization takes place here. Also a passage for the egg from the ovary to the uterus.
The uterus:
Implantation takes place here and also embryo develops here.
The cervix of the uterus: Closes the uterus.
The vagina and Vulva:
Vulva is the external opening of female reproductive system.
It allows mating to take place so that sperms are deposited into the vagina.
The foetus and urine are removed through the vulva.
Pregnancy
is period between fertilization of ova and the expulsion of the foetus through the vulva. Also called gestation period. In cattle gestation period is 270-285 days. Ends with the birth of a calf.
The reproductive tract undergoes a period of rest during which it is repaired and returns to normal. During pregnancy, hormone called progesterone is produced by the placenta to maintain the foetus in the uterus.
| Animal | Length of days |
| Cow | 270-285 Days |
| Sow | 113-117 |
| Ewe/Goat | 150 |
| Rabbit | 28-32 |
Parturition
Act of giving birth called parturition. This time the foetus expelled through the birth canal.
When an animal is about to give birth, it shows signs;-
- Distended udder which produces thick milky fluid called colostrums.
- Swollen vulva producing thick mucus like discharge.
- Loose and slackened pelvic girdle.
- Visible pin bones.
- General restlessness.
Animal parturates within 2-3 hours after this signs. The correct presentation is with the front feet first ,and the head outstretched and resting in between the feet.
Any other presentation called mal-presentation or breech presentation and requires assistance.
Normal Presentation
Reproduction in Poultry
The cock has no penis but a small opening near the vent through which sperms are emitted. Cock has testes within the body.
The hen has elongated oviduct for formation of an egg. Fertilization occurs internally.
During mating the cloaca of the hen and the vent of the cock fit into each other and then semen is poured into the cloaca ,then sucked to the oviducts.
The Reproductive System of a Hen
The reproductive system has the following parts;i). Ovary
ii). Funnel(infundibulum).
iii). Magnum
iv). Ishtumus
V). Uterus/Shell gland
vii) Vaginal
viii). Cloaca
Ovary
Hen has two ovaries but one functional. Ova is formed in ovaries.
About 3500-4000 ova present inside ovary held by follicle. Mature ovum released via rapture of follicle. It moves into oviduct received by the funnel.
Funnel(infundibulum)
Fertilization occurs here. Chalazae also added to yolk.
It also collects the ovum and stores the sperm. Time here is 15 minutes and it is 11.6cm long.
Magnum
Thick albumen is added and stays for 3hrs. its 33cm long.
Isthmus
Its 10.6cm long, Shell membranes added and determines shape of egg.
Water, mineral salts and vitamins added and takes 15 minutes.
Uterus(shell gland)
Calcium deposits i.e.shell added around the egg. Pigments added.
Addition of albumin finished and stays here for 18-22hours.
Vagina
Short, 6.9cm long and for temporal storage of egg before laying
Cloaca
Egg moves out of cloaca through the vent and the cloaca extents out to prevent the egg from breaking.
NB;
Egg formation not depended on fertilization. Egg formation takes 24-26hours.
The components of egg are obtained from body reserves of the hens body.
Selection of Breeding Stock
Selection is used as a tool for livestock improvement. A breeding stock is a group of males and females which act as parents of future generations.
Selection is the process of allowing certain animals to be parents of future generations while culling others.
Culling is the removal of animals which do not perform to the desired level, from the herd. The animals retained have certain desirable characteristics which make them produce more.
Selected animals make up the breeding stock.
The breeding stock should pass the good qualities to their offsprings for better performance, to improve the livestock.
Selection process repeated for many generations increases chances of formation of desirable qualities in an animal.
Genetically termed as gene frequency(occurrence of the genes that carry desirable characteristics.) Selection increases occurrence of desirable genes and decreases occurance of undesirable genes.
During selection, the characteristics to be selected for are first studied closely to ascertain that it is not influenced by the environment, but mainly by the genetic make-up.
Selection helps improve characteristics which are highly heritable.
Heritability means the likelihood of a particular trait to be transmitted to the offspring and they are strongly inherited.
A character like milk yield is lowly heritable, i.e. it is weakly inherited and a bigger percentage of the character is affected by the environment.
The heritability of the character, The intensity with which the selection is done and the interval between generations and kind of selection being practiced.
Factors To Consider When Selecting A Breeding Stock.
- Age
- Level of performance
- Physical Fitness
- Health
- Body Conformation
- Temperament or Behaviour
- Quality of products
- Mothering Ability
- Adaptability
- Prolificacy
Age
- Young animals,
- Those that have not parturated for more than 3-times, should be selected.
- They have a longer productive life.
- Old animals are poor breeders and low producers.
- Production and breeding efficiency decline with age.
Level of performance
- Animals with highest production level selected.
- Performance best indicated by records.
Good performance of animal indicated by;
- High milk, wool and egg production,
- Good mothering ability
- High prepotency which is the ability of a parent to pass good qualities to their offsprings.
- The animals with poor performance should be culled.
- Good records kept and used by the farmer for this purpose.
Physical Fitness
Animals selected should be free from any physical defect e.g.
- mono-eyed,
- limping,
- irregular number of teats,
- scrotal hernia,
- defective and weak backline
Health
- Sick animals do not breed well and are expensive to keep.
- Animals that are resistant to diseases pass these characteristics to their offsprings
Body Conformation
- Animals for breeding to be selected according to proper body conformation.
- A dairy cow should be wedge-shaped with a large udder, thin legs, long neck.
Temperament or Behaviour
- Animals with bad behaviors should be culled. e.g Cannibalism, egg eating, aggressiveness, kicking
Quality of products
- Select animals that give products of high quality such as meat, wool, eggs, milk.
Mothering Ability
- Animals selected should have a good mothering ability,
- That is animals with good natural instinct towards their young ones.
- This will enable them to rear the young ones up to weaning.
Adaptability
Animals selected should be well adapted to the prevailing climatic condition in the area e.g Ardi and semi arid areas.
Prolificacy
- Animals selected should be highly prolific.
- That is, animals with the ability to give birth to many offsprings at a time(larger litter).
- This is a quality that should be considered when selecting pigs and rabbits.
- The ancestry records assist to choose the prolific breedsfor mating
SELECTION OF CATTLE AND SHEEP
Selection in cattle
Consider the following;
Level Of Performance Which Include;
- Milk Yield Buter Content.
- Length Of Lactation Period.
- Calving Intervals.
Age of the Animal, Fertility, physical Fitness, Health Of The Animal, Body Conformation and suitability of the enterprise-milk or beef
Selection in sheep
Consider the following;
Level of performance which includes;
- Mothering ability
- Growth rate
- Wool quality
- Carcass quality
- Twining rate Age
Suitability to the enterprise-wool or mutton
Flocking instinct Health of the animal
Physical fitness
Inheritable defects
Fertility
Inheritable defects.
Fertility.
Selection in Goats
Consider the following:
Fertility.
Mothering ability.
Growth rate.
Twining rate
Carcass quality/dressing percentage
Growth rate.
Suitability to the enterprise - milk or mutton.
Health of the animal.
Age.
Selection in Pigs
Consider the following:
Carcass quality/dressing percentage
Suitability to the enterprise (bacon or pork)
Growth rate.
Health of the animal.
Mothering ability.
Prolificacy.
Number of teats
Temperament.
Body formation.
Age.
Heredity defects
Selection in Camels
Health of the animal.
Age.
Temperament.
Foraging ability.
Fertility.
Level of performance-milk, meat, fur and transport.
METHODS OF SELECTION
These include:
Mass selection - Animals with superior characteristics (highly heritable breeds) are selected from a herd and then allowed to mate among each other at random. The offsprings will show higher performance than their parents. This is because mass selection increases the occurrence of the desirable genes in a population.
Progeny testing - is a offspring resulting from selected parents ( Family selection).In this method a group of progenies (offrprings) are used as an aid to increase accuracy in the selection ofa breeding stock. This is method is used when the character to be selected is of low heritability and expressedby one sex only.This methodtakes upto nine years for the results to be seen
Contemporary comparison
Contemporaries refers to other heifers in the herd sired by the same bull.
This is a progey tasting method which involves comparison of average production of daughters (Heifers) of each bull with that of the other heifer refered to as contemporaries.
In this methods it is assumed that thedifference between the herds of the same breed are non-genetic in origin.
advantages
- It is possible to compare heifers of different ages in different locations worldwide.
- It eliminates difference brought about by the environment.
- it is possible to make direct comparison of stut bulls at different artificial insemiation centres.
- It is accurate since we are using a large herd of animals.
Breeding
Process of mating selected males and females to produce offspring with the desired characteristics.
Reasons:
- To expand the inherited potential of the animal.
- To improve production by introducing new genes.
- To overcome production problems created by the environment.
- To satisfy consumers taste.
- For economic reasons e.g fast growth rate to reach the market early.
Terms Used in Breeding
Inheritance; Genetic transmission of characteristics from parents to offsprings.
The mechanism of inheritance is carried by the sex cells (gametes) and is controlled by genes found in the chromosomes.
Genes are very tiny units of inheritance carrying particular characteristics, such as colour, body shape and amount of milk production. Chromosomes are genetic materials which carry genes.
They exist in pairs paternal and maternal) in the nucleus f the body cells. They are always constant in number.
Dominant and Recessive Characteristics
A dominant gene is one that suppresses the other. It produces a dominant characteristic.
A recessive gene is one that is suppressed by the other. It produces a recessive characteristic.
Hybrid and Hybrid Vigour
A hybrid is an animal which is the product of crossing animals of two different breeds. It has both a dominant and recessive characters. A superior hybrid has 75% dominance and 25% recessive.
Hybrid vigour or heterosis is increased vigour and performance resulting from crossing two superior breeds. When two superior breeds e.g Pedigree friesian and Jersey breeds are mate the resultant offsprings have both the character of high milk yield and high butterfat content. Thus it is said the offsprings have hybrid figure whichis an increased perfomance and figure than both the two parents.
Epistasis
This is the masking of the effect of one gene (reccesive gene) by another gene(dominant) which is non-allelic, that is situated on different locus.
This is aimed at preventing the recesive gene from being expressed.
BREEDING SYSTEMS
They are categorized into two namely; Inbreeding and Outbreeding
1. Inbreeding
Mating of animals which are related i.e have certain alleles of genes in common.
Reasons:
- To increase genetic uniformity in a herd.
- To increase phenotypic uniformity.
- To get proven sires.
- To fix required characteristics when developing a new breed.
- used in animal of higher prepotency (stud Bulls)
It can bring about loss of hybrid vigour.
It may lead to decline in fertility.
It may lead to high rate of pre-natal mortality.
Systems of Inbreeding
Close Breeding: mating between very closely related animals, for example sib-mating and parents sib-mating.
Line Breeding: mating of distantly related animals that had a common ancestor for example cousins, halfbrothers/sisters, grand daughters and grand sires.
2. Outbreeding
Mating of animals which are not related.
Reasons:- To introduce new genes in an existing breeding herd.
- To exploit heterosis resulting from a cross between two breeds.
- To develop a new breed or a grade animal.
Limitations
- Lack of uniformity in animals that result from outbreeding.
- Desirable characteristics may be lost due to variation.
Systems of Outbreeding
i). Cross-breeding
Mating of animals from two different pure breeds to attainhybrid viguor or heterosis such as higher production rate, higher production rate, high growth, disease resistance and heat tolerance.
ii).Out-Crossing
Mating of unrelated animals from the same breed for exxample fresian cow in kenya with Semen of fresian bull from Britain.
iii) Upgrading/Grading up/Backcrossing
Mating where the female of a cow grade stock (locals) is mated with a pure breed sire. The resultant animal is referred to as a high grade.
If the same sire mates with filial generation (F1-6) of its heifers, it will attain a pure breed character. With Artificial insemination (A.I) the systemis used widely to improve the local cattle for better milk production
Mating in Livestock
Mating in Cattle
Heat signs occur every 21 days.
The heat period last for 18-30 hours on average 24 hours.
Cow should be served 12-18 hours after showing the first heat signs.
Heat Signs
Restlessness.
Mounting on others and when mounted on she stands still. Rise in body temperature.
Drop in milk production in lactating cows. Vulva swells and becomes reddish.
Clear or slimy mucus from the vulva.
Bellowing or mooing frequently.
Mating in Pigs
Heat signs in pigs occur after every 21 days. The heat lasts about 72 hours.
Sows or gilts should be served in 18- 36 hours of the heat period.
Signs of Heat
Restlessness.
Frequent urination.
Swelling and reddening of the vulva.
Clear or slimy discharge from the vulva.
Frequent mounting on others.
It responds very well to the 'riding test'.
Mating in Rabbits
Does are ready for mating 6-7 months of age. Heat signs occur every 14 days.
The doe should be taken to the buck and not vice versa.
Signs of Heat
Restlessness.
Frequent urination.
Swollen vulva.
The doe throws herself on the side.
The doe rubs herself against the wall or any other solid object.
The doe tries to contact other rabbits in the next hutch by peeping.
Methods of Service in Livestock
Natural Mating
Advantages:
It is more accurate.
It is less laborious.
Useful when heat signs of females cannot be easily detected.
Disadvantages
Inbreeding is not easily controlled.
Transmission of breeding diseases.
Extra feed for the male is required.
Large males can injure small females.
Wastage of semen.
It is cumbersome and expensive to transport a bull to remote areas.
Artificial insemination
Introduction of semen into the female reproductive tract by artificial means.
Advantages
There is economical use of semen.
It controls transmission of breeding diseases.
Sires that are unable to serve cows due to heavy weight or injury can produce semen to serve cows.
It prevents large bulls from injuring small cows. It reduces the expenses of keeping a male animal.
A small scale farmer who cannot afford to buy a superior bull can have the cows served at a low cost.
Semen can be stored for long. It helps to control inbreeding.
It eliminates the threat of keeping dangerous bulls from the farm.
It makes research work easier.
Disadvantages
Harmful characteristics can be spread quickly by one bull to the offsprings.
It requires skilled labour.
Low chance of conception due to death of semen during storage.
It is laborious:
Embryo Transplant
It is the implantation of an embryo (fertilized ova) from a high quality female (donor) in the uterus of a low grade female (recipient).
Advantages
Faster multiplication of an animal with superior characteristics . It is easier to transport embryos than the whole animal.
Embryos can be stored for a long period awaiting the availability by recipient females.
It stimulates milk production in a female (recipient) that was not ready to produce milk.
Low grade animals can be used in production and rearing of high quality animals. Offsprings of a superior female can spread quickly in an area.
Disadvantages
It is expensive.
It requires skilled personnel.
It requires special equipment for fertilization and storage of embryos.
Signs of Parturition in Livestock
Parturition is the act of giving birth in female animals.
Parturition in Cattle
The gestation period in cattle is 270-285 days averaging 280days.
Signs of Parturition
Restlessness
Enlarged or swollen vulva.
Clear mucus discharge from the vulva.
Slackening of the pelvic muscles.
Full and distended udder.
Thick milky fluid from the teats.
A water bag appears and bursts just before calving.
Parturition in Pigs
The gestation period in pigs is about 4 months or 3 months, 3 weeks and 3 days.
Signs of Parturition
Restlessness.
The vulva turns red and swells.
The udder becomes full with a milky fluid the sow starts to prepare a nest by collecting some beddings at one comer of the pen.
Parturition in Rabbits
The gestation period in rabbits is 28-32 days.
Signs of Parturition
Preparing a nest by plucking off hair from her belly.
Goes off feeding
Restlessness.
The udder distends.