Universitatea de Ştiinţe Agricole şi Medicină Veterinară Iaşi - 632 - RESEARCHES REGARDING THE EFFECT OF PGF 2 α ADMINISTRATION INTERVAL ON COWS ESTROUS SYNCHRONIZATION N. Păcală, I. Bencsik, D. Dronca, S. Acatincăi, I. Petroman, Cornelia Petroman, Ada Cean, I. Carabă, Alexandra Boleman, S. Papp Banat’s University of Agricultural Science and Veterinary Medicine Timisoara e-mail: npacala@animalsci-tm.ro Abstract To improve reproductive efficiency of a dairy farm hormonal treatments for estrus synchronization are used. These allow heat and A.I. grouping to a specific time interval. In our experiments, we studied the estrous and A.I. grouping after the utilization of three hormonal synchronization programs. The protocols consisted of a single administration of PgF2α, to females with known estrous cycle and AI at 5 days interval, the other two protocols, applied to females with unknown estrous cycle, consisted of two doses of PgF2α, administered at 11 or 14 days interval respectively, and heat detection after the second dose administration. There were no significant differences (p>0.05), between the heat manifestation rates, to cows which were stimulated with two doses of PgF2α, at 11 days interval (85.7%), comparing to cows stimulated with two doses of PgF2α at 14 days interval (88.2%). Significant differences (p<0.05) were observed between the heat manifestation rates of cows to which was administrated a single dose of PgF2α (67.1%) and heat manifestation rates at females to which were administrated two doses of PgF2α (85.7-88.2%). Key words: cow, synchronization protocols, PgF2α, estrous, artificial insemination INTRODUCTION Managers of large dairy cattle farms are aware of reproduction efficiency importance for maintaining the farms profitability. The most significant factors involved in reproduction efficiency in a dairy farm are: farm management, physiological and nutritional factors, disease and not at last, reproductive management [3]. In order to improve the rate of heat detection and to increase the pregnancy rate, most often are used hormonal programs to induce and synchronize the estrous. Estrous synchronization is a biotechnical method by which the artificial insemination can be performed for a high number of cows, in a certain interval [1]. The extensively used programs for estrous synchronization are using PgF 2 α and their synthetic analogs. Prostaglandin estrous synchronization is based on the luteolyses effects which induces the functional regression of the corpus luteum, at 24-36 hours after administration [2]. The aim of our work was to induce and synchronize the estrous cycle in dairy cows, to reduce the period from calving to conception, reducing the length of postpartum anestrus. To accomplish our aim we applied synchronization programs based on PgF 2 α and their synthetic analogs. MATERIAL AND METHODS Cows with a normal evolution of the puerperal period were clinically monitored, by transrectal examination, in order to establish the ovaries activity and functional integrity of reproductive tract. Related to ovaries activity, females presenting a corpus luteum on one of the ovaries were considered with known estrous cycle (the luteal phase of estrus cycle). The rest of the females were considered in the category of females with unknown estrous cycle. Females from the experimental groups were synchronized with synthetic analogs of PgF 2 α (Cloprostenol), using the fallowing experimental protocols: - Administration of a single dose of 500 μg Cloprostenol, to females with known estrous cycle, detection of females in heat in the next 5 days and A.I.;