Lifecycles Flashcards
What are the reproductive life cycles of animals?
Fetal –> Neonatal –> Prepubertal –>
Adolescence –> Adult –> Senescence
How is the female reproductive tract formed? (what stops it from becoming a male?)
- No TDF
- Ovaries develop
- No AMH (anti Mullerian hormone)
- Paramesonephric ducts become oviducts, uterus, cervix and part of vagina
- complete female tract
How is the male reproductive tract formed? (what stops it from becoming a female?)
- TDF
- Testes develop
- Sertoli cells secrete anti-mullerian hormone (AMH)
- a.) Degeneration of paramesonephric duct
b. ) AMH causes leydig cells to differentiate (causes 5 onwards) - a.) Testosterone (causes 6a)
b. ) Dihydrotestosterone (causes 6b) - a.) Development of male duct system
b. ) Development of penis, scrotum and accessory sex glands
What causes and infertile female twin in cattle?
- both female and male gonads
- female twin exposed to anti-mullerian hormone in blood supply of male twin which is shared preventing or altering the development of the female tract
How do eggs change throughout life?
- all eggs and number female has is determined by time of birth
- already lost half of eggs by puberty
- got none by menopause
What happens to reproductive activity in infancy?
- in vegetative period - mostly controlled by metabolic hormones
- repro hormone activity is dominated by negative feedback of sex steroids on pituitary keeping the animal in the same repro state (pre puberty)
What happens immediately before puberty happens?
- Peaks of Gn’s gradually increase closer to puberty
- follicles develop and secrete low levels of E2 but ovulation doesn’t occur
- low level spermatogenesis may occur
What is JIVET and why is it used?
Juvenile In Vitro Embryo Transfer
It is used to increase the rate of genetic gain by decreasing generation interval
- cause ovulation and collect ova
- initiate spermatogenesis and collect sperm by testicular biopsy or castration
What significant events happen during puberty of an animal?
Physiological maturation: - easing of neg feedback - development of pos feedback in female Physical Maturation - Growth spurt (influence of steroids) - development of sex organs - production of gametes Behavioural maturation - sexual behaviour and receptivity
What are indicators of puberty in males?
- behavioural traits - mounting and ejaculation
- first ejaculation (voluntary or spontaneous)
- Spermatozoa present in urine and/or ejaculate
- Ejaculate contains threshold numbers of spermatozoa
- male capable of coitus and ejaculating sufficient good quality spermatozoa to result in fertilisation
What are indicators of puberty in females?
- Commencement of cycling - first oestrus
- First ovulation (can be silent)
- Physical maturation to support pregnancy without neg effects on mother
- capable of ovulation of ova which can be fertilised and carried to full term
What initiates puberty (brain)?
Pineal gland and melatonin
- pineal gland secretes melatonin which stimulates GnRH secretion
- manipulation of melatonin levels can cause precocious puberty
What triggers puberty?
neg feedback: both sexes - escape from powerful neg feedback because of change in sensitivity of hypothalamus and pituitary
pos feedback: in female –> rise in oestrogen levels able to trigger pre-ovulatory LH surge
What factors affect puberty?
Age/body weight Nutrition Season Genetic factors Social factors
How does weight and age affect puberty onset?
Generally most animals reach puberty at 1/2 - 2/3 of adult body weight
How does nutrition affect puberty?
- under nutrition delays puberty - protective mechanism against pregnancy
- Severe or prolonged malnutrition - permanent growth issues (potential subfertility (reduced fertility for a long time))
- puberty can be advanced by heavy feeding (except in pigs)
How does season affect puberty in seasonal animals?
Animals must reach appropriate age/ size during a breeding season
What social factors effect puberty and cycling?
- Lee-boot effect - suppresses oestrus (or pseudopregnancies) in large female groups
- Whitten Effect - male intro causes oestrous onset
- Vandenbergh effect - puberty onset in females previously isolated from males but suddenly introduced
- Bruce effect - recently mated rodent females placed with stranger male will return to oestrus (claimed but unconfirmed in other species)
- McClintok effect - menstraul cycle of women spending a lot of time together becomes synchronised
- Male or female effect - male intro causes oestrus onset observed in many (usually seasonal) species
What causes social factors to take effect?
- pheromones (particularly in saliva and sweat)
Why do we artificially induce puberty?
Larger amount of offspring in shorter amount of time without neg effects on mother and neonate
• Economic benefit to hasten puberty and synchronise breeding
• reduced cost of rearing young
• reduced generation interval
Done through social factors and hormones
How is puberty artificially induced?
- Stimulation of follicular growth by exogenous FSH or equine chorionic gonadotrophin (eCG)
- ovulation initiated with LH or human chorionic gonadotrophin (hCG)
- Melatonin can be administered to trigger increased prodution of GnRH, leading to an endocrine cascade triggering puberty
- only works closes to time of normal puberty when secondary organs (e.g. uterus) sufficiently matured
Why do some species only breed in certain seasons?
- repro cycles in some species act as a survival mechanism; efficient growing of species
- ensures offspring is born in favourable environmental conditions (Spring)
- feral species highly seasonal but bred out of some domestic:
- sheep, goats, horses, cats, poultry still somewhat seasonal- cattle, pigs and dogs less so
- males fertile all year round
- females ‘all-or-none’ breeders
- some breeds less seasonal then others (e.g. Merino less seasonal then British sheep breeds)
How does gestation length affect breeding period?
Dog and fox- 2-3 months (short) - late winter/spring
Sheep and goat - 4-5 months (medium) - autumn
Cow and horse - 9-12 months (long) Spring/Summer
How does environmental stimuli effect breeding activity?
- ‘Ultimate’ stimulus related to survival of offspring e.g. temperature
- ‘Proximate’ stimulus triggers breeding activity in the parents
- ‘Obligatory’ Factros - major proximate (immediate) stimulus underlying seasonality and will always cause breeding to start or stop (e.g. change in day length)
- ‘Modifying’ Factors - may modify the precise time of breeding (e.g. nutrition)
What are some of the factors that regulate the breeding season?
Photoperiod
- DAylength change major proximate obligatory stimulus - animals 'long day' and 'short day' breeders - more extreme latitude = more extreme seasons - constant day length (near equator)= either no seasonal breeding (breeding all year round) OR modifying factors become obligatory (required) --> usually nutrition due to monsoon
Temperature (modifying factor)
- few direct effects (except in some wild rodents through heat stress)
- abnormal spermatogenesis (NT cattle)
- libido
- indirect effects through nutrition
Nutrition (Modifying factor)
- few direct effects (except in some wild rodents lacking specific nutrients)
- severe under nutrition:
- may delay oestrus
- silent oestrus
- anovular cycles (no ovulation)
- infertility if specific nutrients lacking - high feeding levels (flushing) may improve fertility in some specie but doesn’t effect timing of breeding
Social stimuli (moderating factor)
- natural phenomenon (deer, sheep)
- male effect. iso from females, reintroduce, can advance breeding season and sync females oestrus
- females also influence male reproduction
- some species need progestrone priming for full oestrus expression & maintenance of subsequent corpora lutea (follicular growth and ovulation may occur without oestrus)
What is the Ran Effect?
introduction of rams can bring ewes into oestrus 2-3 months earlier then they normally would
What is the role of the pineal gland in reproduction?
- neuroendocrine transducer that produces melatonin at night
- melatonin affects GnRH secretion and thus FSH and LH secretion
- no direct effect on gonads
- pos or neg effect depending on species (high melatonin stimulate GnRH production in short day breeders but inhibits in long day breeders)
- pinealectomy abolishes ability to register day length so breeding continues, but at random with regard to day length
How is the breeding season manipulated?
Manipulation of daylength
- from equinox, entend for long day breeders (horses), dcrease for short day (sheep)
- practical only in intensivley housed animals
- works best close to anticipated breeding season, only allows for adjustment, not breeding deep out of season
Administration of melatonin
- Implant in ear delivers melatonin for 6 weeks - advances breeding season when applied 8-12 weeks before normal start - best used together with ram effect
Administration of gonadotrophins
- use PMSG/FSH in non-breeding season (both male/female) - males need well in advance - may need progesterone priming for oestrus and further cycling through CL maintenance - 6 week spermatogenic cycle in males - FSH administration impractical so use frozen semen
Administration of GnRH
- repeat injections to stimulate FSH/LH activity - GnRH agonists (long acting) decrease gonadotrophin secretion in most species - use of GnRH pulses largely ineffective and impossible to carry out
Use of social factors (sheep)
- Ram effect - isolation of sexes for 6 weeks - prime with progesterone to avoid short cycles - first oestrus 22-23 days or 26-27 after ram introduction - prolongs progesterone stimulates oestrus behaviour at first ovulation
What is the process of reproductive senescence?
- reduction in number of breeding opportunities
- polyoestrous animals - more silent heats
- monoestrous animals - increased interval between oestrus cycles - decreased conception rates
- decreased litter size
- increased prenatal losses, dystocia, mismothering and reduced lactation
- increased chromosomal disorders (Down Syndrome)
- Increased spontaneous abortion
- increased aborted fetuses with chromosomal disorders
- human female (abrupt)- deplteion of eggs
- farm animals reduced ability of ovaries and uterus to support preganacy
- males generally fertile till death but fetility declines
- may become physically incapacitated
- gradual decline in sexual interest from peri-pubertal (puberty) stage
Why and how is breeding done from senescent animals?
WHY?
• To pass on maximum genes from valuable animals
HOW?
• Males – collect semen by masturbation, artificial vagina, electroejaculation or testicular/epididymal spermatozoa to use fresh or
frozen
• Females – stimulate ovaries (using FSH/LH or eCG/hCG), perform in
vivo insemination, flush embryos and use surrogates, or collect
oocytes, perform in vitro inseminations and embryo transfer
