Seasonal Breeding in Animals
Seasonal breeding in animals refers to the reproductive strategy where species mate and give birth during specific times of the year to optimize survival and resource availability.
Seasonal breeding in animals is observed in horses, sheep, goats, deer, bears, etc.
In most wild animals the breeding season is initiated at a time when the environment is suitable for the maximum survival of the young at their birth.
Some species have only one period of estrus each year (monoestrous) while some have series of estrous cycles limited to a portion of the year (Seasonally polyestrous).
True seasonal breeding are inherent in ewe, does and mares.
Seasonal Breeding in Sheep and Goats
Most breeds of sheep and goat exhibit seasonal breeding pattern. However, those in the tropics as an exception will cycle throughout the year.
Sheep are short day breeders. Breeding season is initiated with decreasing length of daylight and ends when increasing day length reach a ratio of nearly equal daylight and darkness.
Ewe-lambs and yearling ewes have shorter breeding seasons than older ewes.
The onset of breeding season can be advanced by artificial manipulation of the photoperiod and by use of hormonal agents.
Introduction of rams into a flock during the transition from anestrus to estrus will result in high degree of synchrony in first mating with estrus peaking 15-20 days after introduction of the male.
As with sheep, goats are short day breeders with cyclic activity occurring between late June and early April. Placement of bucks with does just before start of the breeding season will stimulate estrus and result in good synchrony.
Both rams and bucks are affected by photoperiod showing highest breeding activity and fertility in the fall. The day length pattern has a dominant controlling influence on initiation and termination of breeding season.
Seasonal Breeding in Horses
Mares are long day breeders whose seasons are initiated as the ratio of daylight to darkness increases and ends during decreasing day length.
Behavioural estrus that occurs during the short day months from spring to autumn is not frequently accompanied by ovulation.
The seasonal breeding pattern is not as well defined for stallion. Fertile semen can be collected throughout the year.
However, during months of short photoperiod there is a decline in sexual activity and semen production.
Photoperiod Action
The role of photo period in regulating seasonal breeding activity is well established. As breeding season approaches there is an increase in frequency and amplitude of episodic surge of LH.
The sensor of photo periodic response change in mammals is the retina of the eye. The nerve impulse from these photic signals is transmitted from the retina along the retino hypothalamic tract to suprachiasmatic nuclei, located anterior to the hypothalamus, and then to the superior cervical ganglia near base of the brain from which arise the sympathetic nerves that innervate the pineal gland.
The diurnal rhythm of secretory activity of the pineal gland is generated by these suprachiasmatic nuclei. Darkness causes increased sympathetic activity of pineal activity which increases the secretion rate of melatonin whose secretion has been demonstrated only in seasonal breeders.
