Seasonality of Reproduction - Anatomy & Physiology

Introduction

Unlike polyoestrus animals such as the cow or sow which can reproduce all year round some species such as the Mare, Ewe, Goat, Rabbit, Hampster and Doe have an Anoestrus phase to their reproductive cycling. This means that for part of the year they are not experiencing oesrous cyclicity and so are not reproductively active. such animals can be lond or short day polyoestrus breeders. seasonality of reproduction is due to the effect of light levels on the brain. Reproductive seasonality maximises the chance of offspring survival by timing parturition to coinside with spring when nutritional and climate conditions are optimum for lactation and for growth of the offspring.

science of seasonality

During the day lights levels are detected by the Retina which sends impulses to the Suprachiasmatic Nucleus of the Hypothalamus and then to the Superior Cervical Ganglion. Postganglionic nerve fibres synapse with inhibitory nerve fibres within the pineal gland. These fibres cause inhibition of the pinealocyte cells of the Pineal gland preventing synthesis of the hormone Melatonin. At night there is reduced retinal firing and so reduced inhibition of pinealocytes by postganglionic superior cervical gangion fibres and so Melatonin is synthesised and released. Melatonin stimulates the synthesis and release of GnRH from the Hypothalamus leading to pulses of Luteinising Hormone release from the Pituitary gland. which effects the gonadotrophin realsing hormone (GnRH)which increases the

Long day breeders

• the mare
• The mares breeding period is from April-June as these are the months with long hours of sunlight.
• reproductive cycling occurs with the increasing light levels