Oestrous Cycle Pharmacological Manipulation - Anatomy & Physiology

()Map REPRODUCTIVE SYSTEM (Map) FEMALE REPRODUCTIVE TRACT OESTROUS CYCLE

Introduction

The manipulation of normal cyclic activity ensures optimum production or is convenient for the herdsmen or owner. In the case of seasonal breeders, it allows them to breed out of season, or to advance the onset of cyclic activity. There are also advantages in ensuring all animals in a group come into oestrus at the same time for ease of management. There are two methods of oestrus synchronisation. One is physiological manipulation of the oestrous cycle, and the other pharmacological manipulation of the cycle. Various factors must be considered before deciding which method to use. These factors will be specific to the type of production unit and species, also the stage of the natural oestrous cycle in the animal/herd involved.

Factors Influencing Reproduction

Physiological

Light

• Cyclic activity in the mare, ewe, goat and cat depend on changes in the number of daylight hours.
• Tungsten and fluorescent lamps can be used to artificially manipulate the photoperiod.
• Mare and queen are stimulated by increasing day length (long day breeders)
  • If mares are establed in December and exposed to artificial light for increasing duration, the onset of oestrous cyclicity and oculation wil be advanced.
• Ewe and goat are stimulated by decreasing day length (short day breeders)
  • Providing ewes with controlled light housing enables change in the breeding season from autumn and winter to spring and summer.
  • If there is no change in duration of light stiulus, it is possible to make ewes cycle all year round.

Nutrition

• Improved nutrition prior to mating (flushing) will increase the number of follicles which mature and ovulate.
• Used in the ewe and sow successfully.

Other Methods

• The presence of a male can stimulate the onset of cyclic activity in some species (see 'Ram Effect' for more detail).
• In sows and gilts, removing piglets will cause a more rapid return to cyclic activity post-partum.
• If litters are weaned from a group of sows at the same time, there will also be some synchronisation of oestrus.
• Also in gilts and sows, the stress of changing environment or transport stress can stimulate the onset of oestrus post-partum.

Pharmacalogical

Preparations which Stimulate Release of Anterior Pituitary Hormones

• Purified LH and FSH can be extracted from the pituitary gland in the abbatoir, but this is too time consuming to be practiced commercially. There is also the risk of transmitting diseases such as BSE.
• Instead, two substitutes are used commercially:
  • Equine Chorionic Gonadotrophin (eCG): obtained from the serum of pregnant mares. This has an 'FSH-like' effect, but with some 'LH-like' activity.
  • Human Chorionic Gonadotrophin (hCG): obtained from the urine of pregnant women. It has mainly an 'LH-like' effect, but with some 'FSH-like' activity.

Manipulation of the Oestrous Cycle in Various Species

Queen

Pharmacological: Synthetic Progesterone

()Map REPRODUCTIVE SYSTEM (Map) FEMALE REPRODUCTIVE TRACT OESTROUS CYCLE