As a significance of the earth’s rotation about its axis approximately every 24 hours, most organisms on this planet are subjected to probable variations of light and temperature. A diverse range of species, from cyanobacteria to humans, evolved internal biological clocks that allow for the anticipation of these daily variations. The field of chronobiology, the study of the rhythms in plants and animals, was limited to botanists for centuries. Only recently during the last decades, the research was expanded to include animals and later even human beings. Rhythms have been recognized and associated to the fluctuation of day and night and to the succession of the seasons. Nowadays, chronobiology has developed into a multidisciplinary field in which scientists are involved in basic research as well as in applied topics.
Part of the book: Chronobiology
Estrus cycle is a rhythmic change that occur in the reproductive system of females starting from one estrus phase to another. The normal duration of estrus cycle is 21 days in cow, sow, and mare, 17 days in ewe, and 20 days in doe. The species which exhibit a single estrus cycle are known as monstrous and species which come into estrus twice or more are termed polyestrous animals. Among them some species have estrus cycles in a particular season and defined as seasonal polyestrous. It includes goats, sheep, and horses. On the other hand, cattle undergo estrus throughout the year. The estrus inducers can grossly be divided into two parts, that is, non-hormonal and hormonal. Non-hormonal treatments include plant-derived heat inducers, mineral supplementation, uterine and ovarian massage, and use of Lugol’s iodine. The hormones that are used in estrus induction are estrogen, progesterone, GnRH, prostaglandin, insulin, and anti-prolactin-based treatment. Synchronization can shorten the breeding period to less than 5 days, instead of females being bred over a 21-day period, depending on the treatment regimen. The combination of GnRH with the prostaglandin F2α (PGF2α)- and progesterone-based synchronization program has shown a novel direction in the estrus synchronization of cattle with the follicular development manipulation.
Part of the book: Animal Reproduction in Veterinary Medicine