The term "estrous" refers to the point of female sexual excitement in mammals which causes ovulation. At ovulation females are most receptive to mating. This period is commonly referred to as heat. estrous synchronisation is the process of targeting female mammals to come to heat within a short time frame (36 to 96 hours). This is achieved through the use of one or more hormones. GnRH and Prostaglandin F2 are two hormones used in the “Synch” protocols during oestrus synchronisation.  The synchronization of the estrous cycle is often used in the Dairy and Beef industries (and elsewhere) in order to decrease the costs for Artificial Insemination or feeding a bull by reducing the period in which it takes for all cows to be in heat and fall pregnant.
Research has been conducted into different ways farmers can perform estrous synchronization such as progesterone injections or a Progesterone Releasing Intra-vaginal Device [PRID]. The PRID is a sponge that is inserted into the vagina of a cow to stop the natural estrous cycle (for it acts as a corpus luteum), because progesterone is the hormone that signals the body to stop the cycle because fertilisation has occurred. When the sponge is removed the cycle restarts. This apparatus is useful in manipulating the cycle so that multiple cows can be ovulated around the same time. estrous synchronisation has major advantages in making artificial insemination more practical. Increasing the productivity of embryo transfer and artificial insemination is economically profitable as the costs associated with veterinarian and semen services are reduced. The reduction of costs occur because vets are required for less time to do the inseminating because the period of ovulation of the herd is decreased to 2-5 days. There are many different injection methods that have been put into practise in order to manipulate the estrous cycle. These involve injections into each cow with a measured amount of progesterone or progestin and waiting 5-7 days, or until heat signals occur, before moving onto different impregnating methods such as joining the cows or heifers with a bull.
Milk is a product of great demand all year round. As a result of this demand, farmers have been given an incentive to produce milk during winter months. In order to achieve this public demand for milk, dairy farmers needed to change their breeding routines. estrous synchronization enabled this change in the herd’s breeding routine to allow dairy farmers to produce milk for human consumption year round. Case studies for the productivity of these incentives on dairy farms have shown to have positive results. Oestrus synchronisation has proven to have many advantages in the dairy and beef industries. The application of estrous synchronisation enables the farmer to reduce costs involved in the hire of AI technicians and semen import. Concentrated calving and uniform weaning saves time and is cheaper than having individual cows in heat throughout the year. However, there are also disadvantages with estrous synchronisation. It requires a high level of management and skills to be able to manage numerous calving operations at a synchronised time. Furthermore, maintaining nutrition and herd health are major factors when it comes to the achieving optimum reproductive performance through estrous synchronisation.
- TheFreeDictionary.com. 2013. Estrus synchronization. [online] Available at: http://www.thefreedictionary.com/Estrus+synchronization [Accessed: 24 Oct 2013].
- Hopkins, F. and Schrick, F. n.d. ESTROUS SYNCHRONIZATION. [e-book] pp. 1-2. Available through: http://animalscience.ag.utk.edu/Beef/Publications-Beef.html http://animalscience.ag.utk.edu/beef/pdf/EstrousSynchronization-FMH.pdf [Accessed: 28 Oct 2013].
- Bridges, A. 2010. Basics Of Estrous Synchronization In Beef Cattle. Available at: http://search.proquest.com/docview/815996343
- Walsh, R., Leblanc, S., Vernooy, E. and Leslie, K. 2008. Safety of a progesterone-releasing intravaginal device as assessed from vaginal mucosal integrity and indicators of systemic inflammation in postpartum dairy cows. Canadian Journal of Veterinary Research, 72 (1), p. 43
- Dpi.vic.gov.au. 2013. Farmer Case Studies - Department of Environment and Primary Industries. [online] Available at: http://www.dpi.vic.gov.au/agriculture/dairy/handling-and-management/extended-lactation/farmer-case-studies [Accessed: 28 Oct 2013].
- Dejarnette, M. 2004. ESTRUS SYNCHRONIZATION: A REPRODUCTIVE MANAGEMENT TOOL. [e-book] p. 7. Available through: selectsires.com http://www.selectsires.com/resources/fertilitydocs/estrus_syn_reproman.pdf [Accessed: 28 Oct 2013].