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
Updated 2d ago