**3. Fertilisation**

method was named as Ovsynch. Later, this method has been modified by the combined use of both progestagens and prostaglandins and many modified ovsynch protocols have been

74 Success in Artificial Insemination - Quality of Semen and Diagnostics Employed

Nowadays, one of the methods used by the veterinarians to increase the percentage of preg‐ nancy in cows is GnRH and hCG application just before the artificial insemination, together with the insemination or 1st – 15th days after insemination because hormonal balance is very crucial in early embryonic period. Nearly, 25% of cattle embryos die within the first three weeks of pregnancy [4, 13-15]. In this period, continuation of progesterone release by corpus luteum is vital for the life of embryo [16]. For this reason, researchers have strived to keep the progesterone level sufficient enough in early pregnancy by administering GnRH and hCG in different days of estrus cycle. hCG application is done to animals during the insemi‐ nation or luteal period in order to provide the rupture of Graafian follicle, to abolish func‐ tional insufficiencies of corpus luteum and to rise the endogenous progesterone production to the most effective level, and as a result of these applications it has been stated that preg‐ nancy rate has increased in some studies [17-18]. In the same way, with the GnRH applica‐ tion before, during and post insemination in different days, it has been notified that pregnancy rate has been increased by means of stimulating folliculogenesis, ovulation and

The latest method to regulate maternal and fetal relation, to retard or inhibit luteolysis, to maintain high progesterone levels and as a result; to enhance pregnancy rate is application of Nonsteroid Anti-inflammatory Drugs (NSAID) in critical days of pregnancy. Estrus cy‐ cle's hormonal mechanism should be very well known for the good management of this

Cows are polyestrous animals throughout the year. They show estrus within 18-24 day peri‐ ods only if they are not pregnant. Estrus cycle is controlled and managed by hormones re‐

In the start of estrus cycle GnRH plays the most important role [23]. By giving GnRH re‐ leased from hypothalamus in each 30 – 120 minute periods to hypophysis system, it induces synthesis and release of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). With the FSH effect follicles in the ovaries start to grow. Follicular development is ob‐ served in waves. In each wave just one follicle passes to dominant state from the many de‐ veloped follicles, rarely two follicles passes to preovulatory stage. Follicular development or atresia is not seen in other follicles in follicular wave. While estradiol produced from preo‐ vulatory follicle induces LH release, it inhibits FSH release [3, 5, 24]. But FSH release is not only regulated by estradiol and GnRH, inhibin which is an ovary originated peptide also in‐ hibits FSH release just like estradiol. Moreover, activin which is a peptide hormone found in

leased by hypothalamus, hypophysis, ovaries and uterus [22].

follicular liquid induces FSH release, but follistatin inhibits it [5].

derived [11-12].

luteal structures [19-21].

process.

**2. Estrus cycle**

Gestation is a process which starts with fertilisation and completed with birth of the young. Fertilization is the name given to the event of forming a diploid chromosome cell from two haploid chromosome cells by entering of spermatozoon into oocyte [29].

Fertilization takes place in oviduct ampulla in domestic mammals. It happens approximate‐ ly in 12 hours. In the end, zygote forms [30-31].
