Chapter Seven

1. Chapter Seven Heredity and Breeding

2. ALAT Presentations Study Tips • If viewing this in PowerPoint, use the icon to run the show (bottom left of screen). • Mac users go to “Slide Show > View Show” in menu bar • Click on the Audio icon: when it appears on the left of the slide to hear the narration. • From “File > Print” in the menu bar, choose “notes pages”, “slides 3 per page” or “outline view” for taking notes as you listen and watch the presentation. • Start your own notebook with a 3 ring binder, for later study!

3. 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.

4. 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.

5. 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.

6. 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.

7. (Image) Female Internal Reproductive Organs

8. 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.

9. (Image) Embryonic Growth Phases

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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

17. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. Additional Reading Nicholas, F.W. Veterinary Genetics. Iowa State University Press, Ames, IA. 1987.