Environmental Effects on Reproduction Flashcards
What are the 3 types of seasonal breeders?
- Monoestrus = 1 cycle per year, e.g. foxes
- Polyoestrus = several cycles, e.g. cats
- Seasonal polyoestrous = several cycles but limited to certain times within year, e.g. sheep
What are seasonal polyoestrous speeches divided into (photoperiod effects)?
- Long day breeders = enter breeding condition as day length increases in springtime
- Short day breeders = enter breeding condition as day length decreases in autumn
What largely determines when an animal comes into oestrus?
Gestation period
What is phytoperiod?
Day length
Cue to synchronise breeding with season
Why not use temp or rainfall as a cue?
Not as constant + predictable as photoperiod
How is the reproductive cycle synchronised to photoperiod?
- Light exposure to retina is relayed to suprachiasmatic nucleus (SCN) of hypothalamus
- Neurons connect to pineal gland that secretes melatonin
- Melatonin is secreted at night, duration of secretion = length of night
- Pineal gland responds to changes in day length by adjusting secretion of melatonin (longer nights = more melatonin secretion etc)
- Melatonin inhibits GnRH release from hypothalamus, necessary for secretion of LH + FSH
- As day length increases = less melatonin secretion + inhibitory effect on hypothalamus is lifted
- LH + FSH are released + stimulate spermatogenesis or follicular development
Give an example of an animal that shows the importance of the pineal gland + why?
Hamsters
Those without a pineal gland prevents pineal from receiving photo-information are unable to prepare for breeding season
When in high doses + combined with progesterone, what can melatonin suppress?
Ovulation in humans by interfering with GnRH/LH release
In what ways can breeding be manipulated?
- Hormone manipulation - implants of melatonin to seasonally anoestrous ewes mimic short day length (i.e. long nights) + advances onset of breeding
season and normal ovarian cycle by 2-8 weeks
compared to that of untreated ewes - Photoperiod manipulation - Exposing mares to 16L:8D photoperiod (long
day length) after the initial autumnal decrease
in light (i.e. in November/early December)
results in ovulation within about 8 weeks – an
advance of the breeding season of almost 3
months.
- Exposing dairy cattle to long-day lighting
(16L:8D) can increase milk production by 16% - Nutritional manipulation - increasing/decreasing feed intake can advance/retard maturity
- Increasing energy intake before mating can increase ovulation rates
How is heat lost?
- Radiation to environment
- Evaporation (cutaneous + respiratory)
What is heat stress?
If heat gain > heat loss = increase in body temp
Name 5 temp effects on male reproduction
- In bulls + boars, heat stress causes a
decrease in testosterone concentrations - Lower sperm conc
- Reduced acrosome reaction (mice)
- DNA damage in sperm
- Females mated to males exposed to scrotal
heating have smaller foetal and placental
weights
Name 8 temp effects on female reproduction
- Oestrus cycles are shorter in European cattle
in the summer - More frequent periods of anoestrus
- Reduced plasma levels of oestradiol +
lowered follicular oestradiol
concentrations - Altered luteinizing hormone secretion
• Oocyte development is reduced during times
of the year associated with heat stress
• Low fertility rates of oocytes
• Reduced proportion of zygotes developing to
blastocyst stage – less effect at later stages)
• Late gestation (affects foetal growth)
Give 3 temp effects on the foetus
- Reduced foetal and placental growth
- Reduced placental function
- Reduced learning activity in adulthood
(guinea pigs)
Give some nutritional factors that affect reproduction
- Under feeding
