Transcript ALAT Chapter 7

Chapter Seven
Heredity and Breeding
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Breeding and Husbandry
 Genetics deals with heredity.
why offspring resemble or differ from their parents
 Similarities and differences:
due to heredity
caused by environmental factors or mutations
 Successful breeding of animals depends on:
an understanding of basic genetics
breeding system that suits the needs of a particular
protocol.
Genes & Chromosomes
 Physical characteristics of organisms are passed
from one generation to next by genes.
an inherited characteristic such as fur or eye color,
number of toes or the length of the intestine
 Genes are on chromosomes & made of DNA.
 Chromosomes = paired structures in cell nuclei.
Number of pairs differs for various species.
Normal members of a species have = number of pairs.
 Only ova & sperm chromosomes are not paired.
When the ovum is fertilized by the sperm, the zygote
forms paired chromosomes from the unpaired sets.
Half of each parent’s genes passed to next generation.
Expression &
Mutation
 Expression is result of
interaction of paired genes.
 Genes can be either dominant or recessive.
 Recessive brown fur gene & dominant black fur =
expression of dominant black gene (black fur).
 Gene may mutate when passed parent to
offspring.
 Mutations may occur spontaneously or by chemical
& physical environmental factors.
Can be either harmful or beneficial.
 Such animals have potential use as a model to
help understand diseases or phenomena.
Reproduction
 1st step in sexual reproduction is production of
sperm & eggs.
 Fertilization location/manner depend on species.
 In most mammals fertilization occurs within ’s
reproductive tract.
In other types of animals, it occurs outside the body.
 Development site also depends on species.
In most mammals, zygote becomes implanted & grows
in the uterus.
In birds and reptiles, embryonic development usually
occurs outside body, inside an egg.
(Image) Female Internal Reproductive
Organs
Gestation & Estrus
 Time required for a zygote to develop into a fetus
& be born = gestation period.
 Natural end of gestation period called parturition.
 Males produce sperm continually & are ready to
mate almost any time after reaching maturity.
 Females mate only during specific times.
 During estrous cycles, female’s eggs undergo
changes which prepare them for fertilization.
During estrus the female allows mating.
Ovulation usually occurs at or near this time.
Cells in vaginal wall change in phases of cycle.
In some species samples can be collected from the vagina &
examined to determine phase of estrous cycle.
(Image) Embryonic Growth Phases
Breeding Schemes
 Breeding schemes determine how similar or
different parents are from offspring.
Scheme depends on animal & requirements.
 Inbreeding is used to produce animals with
minimal genetic variation.
share characteristics & are identified as specific strain
 Strains are inbred after >20 generations.
 Rodents are the most frequently inbred animals.
C57BL, DBA/2, C3H, and BALB/c
 A mating to an unrelated animal or a different
strain contaminates the inbred line.
Escaped animal should not be returned to a cage.
Breeding Schemes II
 Outbreeding is a scheme of breeding in which
only unrelated animals of the same stock are
mated.
Frequently used in rodent colony management.
Results in maximum genetic difference among
animals.
Usually more vigorous animals & larger litter size.
CF1, ICR, and Swiss
 Other breeding schemes
usually involve mating for
desirable characteristics.
 Animals share a common ancestor = line breeding.
 Cross breeding = mating animals of different breeds.
Mating Systems
 After determining genetic type required for a
project & selecting mating system appropriate to
species being used, more than one mating
system may be appropriate.
 depends on management considerations
 Monogamous mating = 1 & 1 paired together
for the duration of their breeding life.
Simplifies record keeping & lends itself well to
maintaining inbred or outbred colonies.
 Gerbil is bred most successfully with
monogamous pairs.
Harem Mating
 Polygamous mating system = 1
with > 2
s
results in large # of young from least # of breeders
economical method of production
difficult to keep accurate records
 s often share nursing responsibilities, causes uncertainty of
which female gave birth to offspring.
for colonies when not critical to know which is the mother
 Cage must be large enough for adults and young
until offspring are weaned.
 Separate housed & are together for breeding.
Reduces # of animals needed, permits accurate record
keeping, but labor costs are high.
Used when s kill the young or & are aggressive.
Other Breeding Concerns
 Consideration should be given to selection of
good breeding stock.
 Animals should be healthy, young &
nonaggressive.
 Females should exhibit good mothering
characteristics & adequate milk production.
 The health of breeding animals must
be monitored and sign of illness or
disease should be reported immediately.
Maintenance of Breeding Animals
 Rodents & rabbits may desert, kill or cannibalize
their young if disturbed.
Delay cage changes for a few days following birth.
Minimal handling of newborn animals is a general rule.
 Wean ~ 21 days of age in rats and mice.
 Rodents build nests if provided soft paper,
shredded wood fiber or cotton.
 Rabbits require a nest box & pull hair to line nest.
 12–14 hours of light is best for
rodent breeding colonies.
 The longer light period helps
establish consistent estrous cycles.
Record Keeping
 The following are examples of information that
could be kept for a breeding colony:
Breed, strain and type of animal
Parentage or ancestry
Animal identification number
Sex
Date mated
Date of birth and number of offspring
Date weaned and number of offspring
Sex of young
Veterinary information
Animal Identification
 Identify individual animals.
 critical for determining parentage and lineage
 Mixing animals in a cage or placing an animal in
a different cage without proper identification can
be devastating to a research project.
 Cage cards are used to
identify each animal or
group of animals.
 Card contains information about
history, genetic background,
IACUC #, type of experiment & contact.
Short-Term ID
 Clipping or shaving various
locations or patterns
 Nontoxic, waterproof dyes or markers
 Markings, colors, sex, hair or breed
 Collars for cats, dogs and nonhuman primates
Must be routinely checked as animal grows.
Loose-fitting collar could get snagged on cage.
 Dogs and cats purchased from commercial
suppliers have a USDA number on record.
USDA tag may be left on collared animals.
 Collars may cause skin irritation & strangulation &
interfere with neck bandages & other apparatus.
Permanent Identification Methods
 Implantable microchip transponders transmit ID.
Subcutaneous chip implanted
Recording device scans chip and reads #
 Ear notching = holes at various positions
Notches & holes = a numbering code.
Easy to read and produces little trauma to animal.
Used in pigs & rodents, not hamsters & guinea pigs.
Holes or notches close over a period of time.
Sanitize punch tool between animals.
 Toe clipping must have strong justification.
removal of 1st bone of certain toes = a # code
>time, >difficult, >stress than ear marking
Anesthesia is recommended.
Ear & Wing Tags
 Small metal clips are stamped with individual #’s.
 Using special pliers, they are applied near the
base of the ear or to the wing.
 Procedure is quick and causes minimal pain.
 Used on rodents, rabbits, sheep & birds.
 As with ear notching, the ID can be lost.
 In birds a numbered leg band is an alternative to
a wing tag.
Tattooing
 2 types of tattooing devices:
Hand-operated instrument clamps onto ear so pointed
tips pierce skin and ink dyes the underlying tissue.
Electrical pen-like tool has a reciprocating multi-point
needle which marks the skin.
 Ink is massaged into skin perforations.
 Clean & disinfect instruments between animals.
 Ear tattoo ID in rabbits
Avoid damage to medial artery or marginal ear vein.
Use black ink on lighter colored breeds.
 Green ink on dark-colored breeds
Tattoo may spread as animal grows, making the tattoo
unreadable and tattoo may have to be redone.
Tattooing Continued
 Ears - g. pigs, cats, dogs, monkeys & ungulates
 Dogs - ears, skin of flanks or oral cavity
Dogs anesthetized and tattoo area is clipped, washed
& dried.
 Nonhuman primates - chest or inner thigh
 Even individually housed animals should be
tattooed & a cage card posted w/ all other info.
 Neonatal rats & mice may be permanently ID’d
by injecting tattoo ink subcutaneously
into ears, tail, hocks or toes, using
a series or pattern of dots.
Additional Reading
Nicholas, F.W. Veterinary Genetics. Iowa State
University Press, Ames, IA. 1987.