Breeding and Selection Breeding: the mating and production of offspring by animals. The activity of controlling the mating and production of offspring of animals Selection: the act of choosing something or someone from a group Geneus species of livestock European cattle- Bos taurus Zebu Cattle- Bos Indicus Swine- Sus Scrofa Sheep- Ovis Aries Horse- Equus Cabellus Goat- Capra Hircus Dog- Canis Familaris Cat- felis catus Principles of Breeding and Genetics Phenotype: the characteristic of an animal that can be seen or measured Genotype: the genetic makeup of an individual (DNA) Phenotype= Genotype + Environment Genotype= phenotype - Envoromet Selection: differently producing what one wants in a herd. Allowing only certain mating to occur. Inheritance: transmission of genes from parents to offsprings Basic Cell Information Chromosomes: in the nucleus and contains genetic material Gene: an active area in the chromosome that codes for trait DNA: complex molecule of the chromosomes which is the coding mechanism of inheritance Gametogenesis: Process that the gonads produce cells that become gametes(ova and sperm) Spermatogenesis: production of sperm Oogenesis: production of egg or ova Meiosis- special type of nuclear division in which germ cells contain one member of each chromosomes pair Fertilization: when an egg and sperm unite from embryo Each contributes one chromosome per pair to new life Homosygous: an individual whose genes for a particular trait are identical or alike Heterozygous: individual who possesses unlike genes for particular trait Dominant: a gene that overpowers and prevents the expression of its recessive allele when the two alleles are present in a heterozygous individual Recessive: a gene that its expression is masked by dominant allele Allele: gene occupying corresponding loci on homologus chromosomes that affect the same trait What traits should one select? Only traits that contribute to productive efficiency and consumer acceptance are of economic importance Ex: reproduction, growth(pre-weaning, post weaning) Basis of Selection Appearance Genetic abnormalities Estimate carcas merit Fit standard for herd Reproduction record Individuals records Progeny testing Pedigree family Factors affecting genetic progress Selection differential Heritability Genetic interval Accuracy of records Genetic correlation Number of traits in selection program Things to remember about traits Heritability: amount of the phenotypic expression of a trait that is transmitted to offspring (enviroments have big effect) (h2) Heterosis: the tendency of a crossbred individual to show qualities superior to those of both parents Generation interval The average age of the parents when offsprings are born The shorter the generation interval, the faster the genetic interval Selection Methods Tandem Selection: Selection for one trait at a time Least effective: mattes rapid gain in a single trait, but is slow to reach selection goal involving several traits Independant culling: establishes minimum culling levels for each trait makes SLOWER gain for each trait, but reaches goals faster. Most effective when few traits are involved. Selection Index: each animal is rated numerically by combining performance of several traits into a single index New Mexico Ram Test Selection Index Index=12 + 40 (ADG) + 30(CWF) + SL - 12 (DIA) - o.5 (VAR) All variables expressed as ratio of individual to the average ADG= average daily grain CWF= clean wool fibers SL= staple length DIA= Fiber diameter VAR= difference between dide and Britch Breeding Systems Purebred breeder: develop breeding stock that pocessess the highest predictability for transmitting the most desirable inheritance possible purebred animal: meets the requiramnets of a recognized breed and whose ancestors are registered in the herd book of that breed Breed: race or variety of livestock where the members are related by descent and are similar Purebred breeders may use: Linecrossing: crossing different lines or unrelated animals of the same breed, it is also used as outcrossing for outbreeding systems. It results in an increased heterozygosity and heterosis (offspring will not breed true). Heterosis: increase in production in the offspring over average of parents. Inbreeding: mating of related individuals( sires and dams share at least one ancestor) results in a increase of homozygosisty Inbreeding coefficient: measures of how inbred an animal is( the probability two genes of a pair in an individual will be homozygous because they are replicates of a single ancestor gene Coefficient ranges from 0-1. 0=no change, 1=absolute certenity Increase inbreeding usually detrimental to: reproductive performance, pre-weaning growth, post-weaning growth, increase susceptibility to environmental stress Commercial Producers: make use of available genetic material in a manner to maximize production or give most efficient, rapid and economical prodyction possible Systems used by commercial producers Species crossing- how many result in nonfertile offsprings Crossbreeding- mating animals of different established breeds and takes advantage of complementary and heterosis(hybrid vigor) oucrossing/ linerarcrossing- mating of unrelated animals of same breed Grading up- making purebred sires to commercial grade females and their female offspring for several generations Most common species crosses Jack to mare= mule Stallion to jennet= hinny Zebu to european cattle= brangus cattle American bison to cattle= buffalo Cross breeding system- designed to maximize hybrid vigor(heterosis) and produce replacement females throught the rotation of different sire breeds Terminal Static crossbreding system Produces replacement females throught the rotation while taking advantage of producing crossbred offspring Also know as “terminal crossbreeding system” Replacament females can be purchased from or produced in separate population Composiste breeding system Combines desirable traits of two or more breeds of cattle into one package Composition must be carefully planed in order to achieve genetic merit Utilizes hybrid vigor without crossbreeding Systems of mating Determied by: type of facilities, breeding schedule, method of heat detection, genetic program, market target hand/Stud mating Purebred breeders use to control breeding Females are kept apart from the males until desire time of breeding, Horse, Rabbit and Poultry advantages prevents overse of particule sire certainity of mating and to which Sire can increase conception rate by 5-10%. Disadvantages increases labor estrus detection becomes a seven-day a week job Pen mating Males and females coexist throught the breeding seasons or year rounds Used mostly by commercial breeders advantages Minimum labor Heat detection is the responsibility of the sire disadvantages Uncertainty of mating and date of conception Uncertainty of infertile sires and of un-bred females May overwork sires Artificial Insemination referred as AI Process by which semen from male is placed into the reproduction tract of the female using mechanical means rather than by natural source advantages Decrease spreed fo disease Increase number of offspring from superior male Identifies the fertility of sire Reduces number of sires needed Allows mating of small females to larger males Genetic diversity disadvantages Requires trained level of management Increases time and supervision of the female herd for estrus detection Sire training Semen handling and special breeding facilities More costly Embryo transfer Removal of early pregnancy embryos from a genetically superior female and placement of these embryos into reproduction tract of a suitable recipient for gestation and parturition Reproduction defined: process by which animals produce offsrpings for the purpose of continuing the species. The process of reproduction begins with copulation, which is the mating of a male and female of the species Sperm cells from the male are deposited in the female reproduction tract and try to unite with an egg cell When fertilization( a sperm cell and an egg cell units) occurs, an embryo begins The embryo attaches to the wall of the uterus where it is protected, recieves nourishment, and develops When the new offspring reaches the end of the gestation period, it is delivered from the female reproductive tract in a process called parturition

Breeding

The mating and production of offspring by animals.

Selection

The act of choosing something or someone from a group.

Phenotype

The characteristic of an animal that can be seen or measured.

Genotype

The genetic makeup of an individual (DNA).

Chromosomes

Structures in the nucleus that contain genetic material.

Gene

An active area in the chromosome that codes for a trait.

DNA

Complex molecule of the chromosomes that is the coding mechanism of inheritance.

Gametes

The cells produced by gonads that become sperm (in males) and ova (in females).

Spermatogenesis

The process of sperm production.

Oogenesis

The process of egg or ova production.

Meiosis

Special type of nuclear division in which germ cells contain one member of each chromosome pair.

Fertilization

The union of an egg and sperm to form an embryo.

Homozygous

An individual whose genes for a particular trait are identical or alike.

Heterozygous

An individual who possesses unlike genes for a particular trait.

Dominant

A gene that overpowers and prevents the expression of its recessive allele when both alleles are present.

Recessive

A gene whose expression is masked by a dominant allele.

Allele

A gene occupying corresponding loci on homologous chromosomes that affect the same trait.

Heritability

The amount of the phenotypic expression of a trait that is transmitted to offspring.

Heterosis

The tendency of a crossbred individual to show qualities superior to those of both parents.

Generation interval

The average age of the parents when offspring are born.

Tandem Selection

Selection for one trait at a time.

Independent culling

Establishes minimum culling levels for each trait, making slower gain for each trait but reaching goals faster.

Selection Index

Combines performance of several traits into a single numerical index to rate animals.

Purebred breeder

Develop breeding stock that possesses the highest predictability for transmitting desirable inheritance.

Heterosis

Increase in production in the offspring over the average of parents.

Inbreeding

Mating of related individuals resulting in an increase of homozygosity.

Commercial Producers

Make use of available genetic material to maximize production efficiently.

Artificial Insemination

The process of placing semen from a male into the reproductive tract of a female using mechanical means.

Embryo Transfer

Removal of early pregnancy embryos from a genetically superior female and placing them into a suitable recipient.

Scrotum

A two-lobed sac that contains and supports the testes.

Testes

Paired organs that produce sperm and testosterone.

Epididymis

Coiled tube attached to each testicle responsible for maturation and storage of sperm.

Vas Deferens

Transports sperm from the epididymis to the urethra.

Accessory Glands

Secretes fluids that provide energy and buffers to sperm; includes seminal vesicles and prostate gland.

Penis

Passageway for semen and urine that deposits semen in the female reproductive tract.

Spermatogenesis

The continuous process by which sperm is formed, occurring in the seminiferous tubules.

Poultry Anatomy

Differences include testes located in the abdominal cavity and papillae as copulatory organs.

Age of Puberty

The age at which different species reach sexual maturity.

Fibroelastic Penis

Penis primarily composed of connective tissue, found in bulls, rams, and boars.

Vascular Penis

Penis supplied with blood vessels, found in stallions.