*5.2.2 Progesterone treatment*

High levels of progesterone in the female's system are maintained with the help of progestogens [33], even after the regression of the corpus luteum. After the progestin removal, synchrony of estrus occurs up to 2–5 days. Melengestrol acetate (MGA) (oral feeding), Syncro-Mate-B (SMB) (ear implant), and CIDR (intravaginal device) are the commercial products which fall into this category. The longer the progestin was administered to cattle, the higher the rate of estrous synchronization, but the fertility of the synchronized animals was lower. Kaltenbach et al. [34] and Wiltbank [35] reported that the estradiol was luteolytic when administered early in the bovine estrous cycle. Combining progestin treatment and estradiol administration at the initiation enabled the period of progestin to be shortened (9–14 days) without reducing the percentage of animals exhibiting a synchronized estrus. This treatment regimen was the basis for the commercial products Syncro-Mate-B, PRID, and CIDR. Administration of progestin at "sub-luteal" levels demonstrated that it inhibits estrus and ovulation and synchronizes estrus in cattle, but that a persistent, estrogen-secreting follicle develops when progestin treatment extends the estrous cycle [36].

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*Induction and Synchronization of Estrus DOI: http://dx.doi.org/10.5772/intechopen.90769*

c.Application of CIDR.

responding to treatment.

*5.2.3 GnRH-based treatment*

*5.2.2.1 Techniques of progesterone treatment*

a.MGA feeding: MGA was added to feed such that females received 0.5 mg/head/ day for 14 days and if MGA was administered, cyclic females begin to show estrus. This estrus was subfertile, and it was recommended that females should

b.Syncro-Mate-B (ear implant) treatment late in the estrous cycle (>14 days) in cow gives lower conception rates. The ideal time for SMB treatment to begin is between the 8th and 12th day of the estrous cycle to maximize estrus response.

CIDR insert for cattle is made by molding a thin layer of silicon and progesterone mixture (10% w/w) around a nylon spine under high temperature. It contains 1.38 g progesterone and is designed to maintain higher blood concentrations of progesterone to at least 2 ng/ml for up to 10 days. The CIDR is easily inserted into the vagina and has good retention capacity (2.5% loss rate is normal); a flexible nylon tail is attached to it for easy removal. The CIDR provides an exogenous source of the progesterone, and its removal on treatment day 7 results in a rapid fall in plasma progesterone levels, which results in estrus synchronization in those animals

Estrus synchronization and fertility with a combination of GnRH and prostaglandin F2α are good for cyclic females, and this combination may induce cyclicity in cows experiencing postpartum anestrus [20]. The new methods of estrus synchronization more precisely and control the time of ovulation more exactly in order to allow a single, timed insemination without the need for detection of behavioral estrus. Administration of GnRH during the estrous cycle in bovines causes regression or ovulation of the dominant follicle and initiates the emergence of a new wave of follicular growth [20]. Ovsynch, CO-Synch, Select-Synch, and Hybrid-Synch are the four systems for synchronization of estrus with GnRH-PG combinations.

At day 1 GnRH injection is used to program follicle growth in cyclic females and to induce ovulation in anestrous females, and PGF2α on day 8 induces regression of CL that is present to cause a decline in progesterone. Then on days 10–11, the second GnRH is given which induces ovulation of dominant follicles that have been preprogrammed by the first GnRH treatment. The major GnRH programs that do

a.GnRH-PGF system: This represents the simplest GnRH-based system. A

b.GnRH-PGF + GnRH system: This system is a GnRH-PGF system in which second GnRH injection is given to all or some cows between 48 and 72 hours

after PGF (days 2–3), with timed AI on all or a portion of the herd.

common name for this system is "Select-Synch." In this system a single dose of GnRH and prostaglandin was injected on day 1 and day 8, respectively. Some cows (8%) exhibit estrus up to 48 hours before PGF (day 6). The early estrous are fertile and cows can be inseminated 12 hours after detection. The peak estrous response occurs 2–3 days after PGF with a range of 1–5 days. With this system, a minimum of 5 days of estrous detection after PGF and 2 days prior

not involve use of the CIDR are described as follows:

PGF is required to detect most heats.

be bred on the second estrus following MGA removal [37].
