Agriculture Form 3 – Livestock Production III… (Selection and Breeding)

Introduction

• The breeding of animals is under human control, and breeders decide which individuals shall produce the next generation.
• The breeder makes a choice based on desired traits.
• Animal breeding is based on the fact that certain qualities are genetic; hence valuable qualities are passed from parents to offspring.
• These qualities can be maintained or improved in the next generation through selective breeding.

The Performance of an Animal Is Influenced by Two Major Factors:

• Genetic potential
• The environment, which includes:
  • Feeding
  • Health
  • Care
  • 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.
• They transmit these superior characteristics to their offspring.
• When this process is repeated over a long period, it results in livestock improvement.

Reproduction and Reproductive Systems

• Reproduction is the process by which offspring are produced.
• All farm animals multiply by sexual reproduction.
• It begins with fertilization, the fusion of male and female gametes to form a zygote.
• Fertilization takes place internally in the female’s body.
• The embryo (zygote) develops inside the mother, fed and protected until the end of gestation.
• In poultry, eggs are fertilized internally but laid externally, with chick development occurring during incubation.
• Both males and females have specialized reproductive organs.
• Some organs secrete fluids necessary for gamete movement and survival.

Reproduction in Cattle

• The male reproductive organs produce spermatozoa (male gametes).
• Sperm are introduced into the female reproductive system, where they fuse with the ovum to form a zygote.

• The Testis:
  • Two testes hang loosely between the hind legs.
  • Enclosed by loose skin called the scrotum, which regulates temperature for optimum sperm production.
  • Produce spermatozoa stored in a coiled tube called the epididymis.
• Epididymis: Storage of spermatozoa.
• Sperm Ducts:
  • Convey sperm from the testis and urine through the penis.
  • Sphincter muscles contract to allow each to pass separately.
• Seminal Vesicles: Produce fluid called semen.
• Semen carries sperm out of the penis in fluid form.

• Prostate Gland: Produces fluid that neutralizes the acidic effects of urine in the urethra, preventing sperm death.
• Accessory Glands: Include seminal vesicles, Cowper’s gland, and prostate gland.
• Urethra: Conveys urine and semen.
• Penis:
  • Surrounded by a sheath, an extension of skin.
  • Introduces sperm into the cow’s vagina through the vulva during mating.
  • Functions as a copulatory organ and for urination.

Ovaries and Fallopian Tubes (Oviduct)

• Two ovaries located in the abdomen, left and right.
• Produce ova (eggs) and hormones controlling the sexual cycle.
• Oestrogen produced by the Graafian follicle induces oestrus (heat), causing the cow to show signs of heat.
• Every 21 days, the ovary releases a mature ovum and the cow comes into heat.
• The ovum travels through the fallopian tubes to the uterus.
• This release and movement of the ovum is called ovulation.
• If mating occurs at this time, fertilization takes place.
• The fertilized egg implants onto the endometrium (uterine wall) and develops into a fetus.

Fallopian Tubes:

• Site of fertilization.
• Passage for the egg from ovary to uterus.

The Uterus

• Embryo develops here.
• The cervix: Closes the uterus.

The Vagina and Vulva:

• Vulva is the external opening of the female reproductive system.
• Allows mating so sperm are deposited into the vagina.
• The fetus and urine are expelled through the vulva.

Pregnancy

• Period between fertilization of ova and expulsion of the fetus through the vulva.
• Also called the gestation period.
• In cattle, gestation lasts 270-285 days.
• Ends with the birth of a calf.
• The reproductive tract rests, repairs, and returns to normal after birth.
• During pregnancy, the hormone progesterone is produced by the placenta to maintain the fetus in the uterus.

Parturition (Giving Birth)

• Parturition is the act of giving birth.
• The fetus is expelled through the birth canal.

Signs an Animal Is About to Give Birth:

• Distended udder producing thick milky fluid called colostrum.
• Swollen vulva producing thick mucus.
• Loose and slackened pelvic girdle.
• Visible pin bones.
• General restlessness.
• Parturition usually occurs within 2-3 hours after these signs.
• The correct presentation is front feet first, with the head outstretched between the feet.
• Any other presentation is called mal-presentation or breech presentation and requires assistance.

Reproduction in Poultry

• The cock has no penis but a small opening near the vent through which sperm are emitted.
• The cock’s testes are located within the body.
• The hen has an elongated oviduct for egg formation.
• Fertilization occurs internally.
• During mating, the cloaca of the hen and vent of the cock fit together, allowing semen to enter the cloaca and then the oviduct.

The Reproductive System of a Hen

Ovary

• Hen has two ovaries but only one is functional.
• Ova are formed in the ovary.
• There are 3500-4000 ova inside the ovary held by follicles.
• Mature ovum is released via rupture of a follicle.
• The ovum moves into the oviduct, received by the funnel.

Funnel (Infundibulum)

• Fertilization occurs here.
• Chalazae are added to the yolk.
• Egg stays here for about 15 minutes.
• The funnel is approximately 11.6 cm long.

Magnum

• Thick albumen (egg white) is added.
• Egg stays here for about 3 hours; the magnum is 33 cm long.

Isthmus

• Approximately 10.6 cm long.
• Shell membranes are added.
• Determines the shape of the egg.
• Water, mineral salts, and vitamins are added.
• Egg stays here for about 15 minutes.

Uterus (Shell Gland)

• Calcium is deposited to form the shell around the egg.
• Pigments are added.
• Albumin addition is completed.
• Egg stays here for 18-22 hours.

Vagina

• Short, about 6.9 cm long.
• Temporary storage of the egg before laying.

Cloaca

• Egg moves out through the cloaca and vent.
• The cloaca extends to prevent the egg from breaking during laying.

Note:

• Egg formation does not depend on fertilization.
• Egg formation takes 24-26 hours.
• Egg components are obtained from the hen’s body reserves.

Selection of a Breeding Stock

• Selection is a tool for livestock improvement.
• A breeding stock is a group of males and females acting as parents of future generations.
• Selection involves allowing certain animals to be parents while culling others.
• Culling removes animals that do not perform to the desired level.
• Retained animals have desirable characteristics that make them produce more.
• Selected animals form the breeding stock.
• The breeding stock should pass good qualities to offspring for better performance and livestock improvement.
• Repeated selection over generations increases the chances of desirable qualities forming in animals.
• Genetically, this is termed gene frequency (occurrence of genes carrying desirable traits).
• Selection increases desirable genes and decreases undesirable ones.
• Characteristics selected should be mainly influenced by genetics, not environment.
• Selection improves highly heritable traits.
• Heritability is the likelihood a trait is transmitted to offspring.
• Traits like milk yield are lowly heritable, meaning environment affects them more.

The Degree to Which Selection Affects a Character Depends on the Following Factors:

• The heritability of the character.
• The intensity of selection.
• The interval between generations and the type of selection 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

• Select young animals.
• Those that have not parturated more than three times are preferred.
• 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 the highest production level are selected.
• Performance is best indicated by records.

Good Performance Is Indicated By:

• High milk, wool, and egg production.
• Good mothering ability.
• High prepotency, the ability of a parent to pass good qualities to offspring.
• Animals with poor performance should be culled.
• Good records should be kept and used for selection.

Physical Fitness

Animals selected should be free from physical defects such as:

• Mono-eyed condition
• Limping
• Irregular number of teats
• Scrotal hernia
• Defective or weak backline

Health

• Sick animals do not breed well and are expensive to keep.
• Disease-resistant animals pass resistance to offspring.

Body Conformation

• Animals should have proper body conformation for breeding.
• A dairy cow should be wedge-shaped with a large udder, thin legs, and a long neck.

Temperament or Behaviour

• Animals with bad behaviour should be culled, such as:
• Cannibalism, egg eating, aggressiveness, kicking.

Quality of Products

• Select animals that produce high-quality products.

Mothering Ability

• Animals should have good mothering ability.
• They should have a natural instinct to care for their young.
• This enables them to rear young up to weaning.

Adaptability

• Animals should be well adapted to the prevailing climatic conditions.

Prolificacy

• Animals should be highly prolific.
• This means the ability to give birth to many offspring at a time (larger litter).
• This is especially important when selecting pigs and rabbits.

Selection in Cattle and Sheep

Selection in Cattle

Consider the Following:

• Level of performance including:
• Milk yield and butter content
• Length of lactation period
• Calving intervals
• Age of the animal
• Fertility
• Physical fitness
• Health
• Body conformation
• Suitability for milk or beef enterprise

Selection in Sheep

Consider the Following:

• Level of performance including:
• Mothering ability
• Growth rate
• Wool quality
• Carcass quality
• Twinning rate
• Age
• Suitability for wool or mutton enterprise
• Flocking instinct
• Health
• Physical fitness
• Inheritable defects
• Fertility

Selection in Goats

Consider the Following:

• Fertility
• Mothering ability
• Growth rate
• Twinning rate
• Carcass quality/dressing percentage
• Suitability for milk or meat enterprise
• Health
• Age

Selection in Pigs

Consider the Following:

• Carcass quality/dressing percentage
• Suitability for bacon or pork enterprise
• Growth rate
• Health
• Mothering ability
• Prolificacy
• Number of teats
• Temperament
• Body formation
• Age
• Heredity defects

Selection in Camels

• Health
• Age
• Temperament
• Foraging ability
• Fertility
• Level of performance for milk, meat, fur, and transport

Method of Selection

These Include:

• Mass Selection: Animals with superior characteristics are selected from a herd and allowed to mate among themselves.
• Progeny Testing: Assessing an animal’s breeding value based on offspring performance.
• Contemporary Comparison: Comparing performance between heifers of the same age and sexual maturity.

Breeding

• Process of mating selected males and females to produce offspring with desired characteristics.

Reasons for Breeding

• To expand the inherited potential of the animal.
• To improve production.
• To overcome production problems caused by the environment.
• To satisfy consumer preferences.
• For economic reasons.

Terms Used in Breeding

Inheritance

• Genetic transmission of characteristics from parents to offspring.
• Inheritance is carried by sex cells (gametes) and controlled by genes in chromosomes.
• Genes are tiny units carrying specific traits such as color, body shape, and milk production.
• Chromosomes carry genes and exist in pairs (paternal and maternal) in the nucleus of body cells.
• The number of chromosomes is constant.

Dominant and Recessive Characteristics

• A dominant gene suppresses the other and produces a dominant trait.
• A recessive gene is suppressed and produces a recessive trait.

Hybrid and Hybrid Vigour

• A hybrid is an animal produced by crossing two different breeds.
• Hybrid vigour (heterosis) is increased vigor and performance from crossing two superior breeds.

Epistasis

• Masking of one gene’s effect by another non-allelic gene located at a different locus.

Breeding Systems

Inbreeding

• Mating of related animals.
• Reasons:
• To increase genetic uniformity in a herd.
• Used to fix desired characteristics in new breeds.
• To increase phenotypic uniformity.
• To obtain proven sires.

Limitations

• Loss of hybrid vigour.
• Decline in fertility.
• High rate of prenatal mortality.

Systems of Inbreeding

• Close Breeding: Mating between very closely related animals, e.g., siblings or parent-sibling.
• Line Breeding: Mating of distantly related animals with a common ancestor, e.g., cousins.

Outbreeding

• Mating of unrelated animals.

Reasons:

• To introduce new genes into an existing herd.
• To exploit heterosis from crossing two breeds.
• To develop new breeds or grade animals.

Limitations

• Lack of uniformity in offspring.
• Desirable traits may be lost due to variation.

Systems of Outbreeding

• Cross-breeding: Mating animals from two different pure breeds.
• Out-crossing: Mating unrelated animals from the same breed.
• Upgrading/Grading Up: Mating a local female with a pure breed sire to produce a high-grade animal.

The resultant animal is called a high grade.

Mating in Livestock

Mating in Cattle

• Heat signs occur every 21 days.
• Heat period lasts 18-30 hours, averaging 24 hours.
• Cow should be served 12-18 hours after first heat signs.

Heat Signs

• Restlessness.
• Mounting others and standing still when mounted.
• Rise in body temperature.
• Drop in milk production in lactating cows.
• Swollen, reddish vulva.
• Clear or slimy mucus discharge from vulva.
• Frequent bellowing or mooing.

Mating in Pigs

• Heat signs occur every 21 days.
• Heat lasts about 72 hours.
• Sows or gilts should be served 18-36 hours into the heat period.

Signs of Heat

• Restlessness.
• Frequent urination.
• Swelling and reddening of vulva.
• Clear or slimy vulva discharge.
• Frequent mounting on others.
• Responds well to the ‘riding test’.

Mating in Rabbits

• Does are ready for mating at 6-7 months of age.
• Heat signs occur every 14 days.
• The doe should be taken to the buck for mating, not vice versa.

Signs of Heat

• Restlessness.
• Frequent urination.
• Swollen vulva.
• The doe lies on her side.
• Rubs herself against walls or solid objects.
• Attempts to contact other rabbits by peeping.

Methods of Service in Livestock

Natural Mating

Advantages

• More accurate.
• Less laborious.
• Useful when heat signs are difficult to detect.

Disadvantages

• Inbreeding is not easily controlled.
• Transmission of breeding diseases.
• Extra feed required for the male.
• Large males can injure small females.
• Wastage of semen.
• Transporting bulls to remote areas is cumbersome and expensive.

Artificial Insemination

• Introduction of semen into the female reproductive tract by artificial means.

Advantages

• Economical use of semen.
• Controls transmission of breeding diseases.
• Sires unable to serve due to injury or weight can still produce semen.
• Prevents injury to small cows by large bulls.
• Reduces expenses of keeping a male animal.
• Affordable for small-scale farmers.
• Semen can be stored for long periods.
• Helps control inbreeding.
• Eliminates the need to keep dangerous bulls on the farm.
• Facilitates research work.

Disadvantages

• Harmful traits can spread quickly from one bull to many offspring.
• Requires skilled labor.
• Low conception chance if semen dies during storage.
• Laborious process.

Embryo Transplant

• Implantation of an embryo from a high-quality female (donor) into the uterus of a low-grade female (recipient).

Advantages

• Faster multiplication of animals with superior traits.
• Easier to transport embryos than whole animals.
• Embryos can be stored awaiting recipient availability.
• Stimulates milk production in recipient females not ready to produce milk.
• Allows use of low-grade animals for rearing high-quality offspring.
• Offspring of superior females spread quickly in an area.

Disadvantages

• Expensive.
• Requires skilled personnel.
• Needs special equipment for fertilization and embryo storage.

Signs of Parturition in Livestock

• Parturition is the act of giving birth in female animals.

Parturition in Cattle

• Gestation period is 270-285 days, averaging 280 days.

Signs of Parturition

• Restlessness.
• Enlarged or swollen vulva.
• Clear mucus discharge from vulva.
• Slackening of pelvic muscles.
• Full and distended udder.
• Thick milky fluid from teats.
• Appearance and bursting of water bag just before calving.

Parturition in Pigs

• Gestation period is about 4 months (3 months, 3 weeks, and 3 days).

Signs of Parturition

• Restlessness.
• Reddening and swelling of vulva.
• Full udder with milky fluid; sow prepares a nest by collecting bedding.

Parturition in Rabbits

• Gestation period is 28-32 days.

Signs of Parturition

• Preparing a nest by plucking hair from belly.
• Loss of appetite.
• Restlessness.
• Udder distension.