Bovine Estrus Synchronization

The next step in the evolution of synchronization protocols was the use of prostaglandin (PGF) to reduce the luteal phase [16]. This method consists of the use of two doses of PGF applied with an interval of 12 to 14 days. The PGF causes the regression of mature CL [ 16]. After 48 hours of the second dose, the estrus is detected and artificial insemination can be performed during 2-3 days. The application of this method together with lA without heat detection presents variable results in heifers and poor results in cows with calves [16]. The success of the treatment with prostaglandin depends on the herd cyclicity and the stage of development of the dominant 

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Bovine estrus synchronization is an important field for the veterinary pharmaceutical industry. A description of the natural bovine cycle and methods to cycle control are presented. In addition, commercially available silicone devices for bovine estrus synchronization are listed. The mathematical modeling of progestagens release from such devices is a crucial tool in the development of novel and/ or optimized delivery systems. For this purpose, several in vitro models, approaches to explain the ADME processes and overall models are described. This type of mathematical modeling could help in the future to customize drug delivery systems to specific animals and/ or situations. 

Keywords Silicone, drug delivery, mathematical modeling, controlled release, bovine estrus synchronization... 

Table 15.4 presents some of the intravaginal veterinary drug delivery systems for bovine estrus synchronization. These devices contain progesterone uniformly distributed throughout the silicone matrix. As mentioned before, the initial progesterone load is higher than hormone solubility in the matrix to meet the therapeutic requirements. 

Table 15.4 Intravaginal silicone devices for bovine estrus synchronization.

In bovine estrus synchronization, the medn objective is to develop a formulation that presents a relecise rate between specific therapeutic ranges, to meet the therapy requirements. In this context, the use of both in vitro and in vivo mathematical models is of critical importance to assist and facilitate these tasks. 

In the bovine estrus synchronization therapy, as was mentioned previously, supraluteal levels of progesterone (>lng ml ) are obtained a short time after the insertion of silicone devices due to a quick absorption of the hormone through the vaginal wall, followed by a complex but fast distribution to the circulatory system. One challenge in developing... 

Prostaglandins are known to occur ubiquitously In mammals. Among these, prostaglandin type has been extensively studied In association with Its use In causing regression of the corpus luteum (1-3). Synchronization of estrus and ovulation In cows have been achieved by discriminate administration of PGF2a l he mechanisms of bovine luteolysis have been described In detail (4). The estrus cycle synchronization has an obvious advantage when used In conjunction with artificial Insemination In cows. 

In those cases where a long-term physiological semiochemical effect (primer pheromone effect) can be monitored, such problems do not arise. Such an effect (synchronization of estrus) has been assigned to estrous bovine cervical mucus (Izard, 1983). 

R.L. Larson, and R.F. Randle, The bovine estrous cycle and synchronization of estrus. College of Veterinary Medicine, Kansas State University, USA, 2006. 

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