Explain the connection between shortening day length and the onset of oestrous in sheep. - Leaving Cert Agricultural Science - Question (f) - 2009

Sheep are classified as seasonal breeders, particularly during the autumn or winter months, typically from August to December. The reduction in daylight hours acts as a crucial environmental cue that triggers physiological changes in the sheep.

Declining light levels are detected by the eyes and transmitted to the brain, more specifically to the hypothalamus. This region of the brain processes the information regarding the change in light.

Upon receiving this signal, the hypothalamus then communicates with the pineal body, which is responsible for melatonin production. During shorter days, there is an increase in melatonin levels. This elevated melatonin stimulates the anterior pituitary gland to release Follicle Stimulating Hormone (FSH).

FSH plays a vital role in stimulating the ovaries, leading to the production of estrogen. Increased estrogen levels are necessary for initiating and regulating the estrous cycle, preparing the sheep for reproduction. Therefore, the connection between shortening day length and the onset of oestrous in sheep lies in this complex hormonal response triggered by changes in daylight.