seasonal breeding

how can temperature reduce fertility

• altered ovarian follicle dynamics

• incresed oocyte polyploidy and altered oviducal function leading to:

• 
  - fertilisation failur

• - early embryonic death

• - changes in oestrus behaviour

problems in high yielding dairy cow

• high milk yield →NEB→metabolic stress→ decrease in metabolic hormones

how do external signals influence seasonal reproduction

pineal gland

• where is it located

• what does it secrete and from what. when is the synthesis of this the greatest

• what is the rate limitng enzyme

• located in brain between two cerebral hemispheres

• varies in size between species but not location secretes melatonin

• melatonin is sytheissed in the pinela gland from tryptophan

• rate limiting enzyme is N acetyl- transferase

• rate of melatonin sytneiss is greatest during the hours of darkness

neural input

• where is photic stimuli relayed from which cells

• via which trat to which nucleus

• then which neurons

• then which ganglion to which gland

• photic stimuli relayed from retinal ganglion cells via retinohypothalamic tract → supraciasmatic nucleus (anterior hypothalamus) → periphreal and central sympathetic neurons and superior cervical ganglion →pineal gland

• more light equals more -ve feedback on pineal so less melatonin

what does rainfall regulate

• seasonal patterns of pregnancies in macropods

influence of sex

• females more strongly seasonal than the male

• timing of the breeding season may not be exactly the same

• male fertility is influenced by season and photoperiod

• eg in sheep daily production of spermatozoa during spring is 4x lower compared autumn

influence of genotype on seasonality

• interaction with genotype

• sometimes out of sync with latitude

• so lambs can be born outside of spring

non seasonal vs seasonal

• where is nonseasonal reproduction mainly observed

• when do seasonal breeders develop gonads and display reproductive behaviour

• which 2 factorsdetermine the timing in mating

Nonseasonal reproduction is mainly observed in animals inhabiting tropical areas, where annual environmental changes are relatively small. Animals in these areas exhibit reproductive behaviour all year round.

• In contrast, seasonal breeders develop gonads and display reproductive behaviour during specific times of the year in order to limit the delivery of offspring between spring and early summer.

• These seasons are optimal for raising offspring because the climate is moderate and sufficient food is available.

• A critical factor in determining the timing of mating is the gestation length or incubation of fertilized eggs

seasonal species

• sheep

• goat

• deer

• horse

• cat

• wild pig

• hamster

• rabbit

non seasonal species

• dog

• cow

• pig

• guinea pig

• rodent

when are reproductive behavours in LH or SD breeders observed

when the light phase lasts longer than the critical day or night length

what is same and different between species

long and short days

• what does melatonin act on

• what happens in long days

• what happens in short days

• what happens as a result of long days

1. light signals the hypothalamus and controls pineal gland and either melatonin increases or decreases

2. melatonin acts on the pars tuberalis of the pituitary

3. in LONG DAYS pars tuberalis cells increase TSH which activates DIO2 in tanycytes.This converts t4 (inactive) to t3.

4. in SHORT DAYS melatonin suppresses PT activity so low TSH, DIO2 and T3

5. the increased T3 in LONG DAY increases kisspeptin ( by stimulating apidocytes to produe and secrete leptin) , RFRP 3 stimulates so increased GnRH, FSH, LH

6. in SHORT DAYS the decreased T3 decrease kisspeptin, as kisspeptin neurones are inhibted by RFRP3

7. therefore RFRP-3 has different effects in short and long day breeders

the opposite effects of RFRP3

• in short day what is RFRP3 and how is it inhibited

• in long day, and how is it activated

• in short day breeders like sheep, RFRP3 is inhibitory to GnRH production. therefore for the start of breeding season this peptide has to be inhibited.

  • high melatonin during short by pineal gland inhibits RFRP3.

• in long day like mare RFRP3 is stimulatory

  • low melatonin during long days increases TSH DiO2 and T3 leading to activation of RFRP3