Equine chorionic gonadotrpin: biological potency of different products and reproductive performance of cows treated with the hormone at crescent sub-doseso

Abstract

equine chorionic gonadotropin (eCG) is a hormone commonly used to improve the efficiency of protocols for fixed time artificial insemination (TAI) in cattle. However, eCG treatment often do not improve the reproductive performance. Our working hypothesis is that commercial eCG products may have different biological potency, so, pregnancy variation could be also attributed to the eCG product and/or dose of eCG used. This project aims to evaluate the biological activity of different eCG products as well as the reproductive efficiency of cows treated with crescent sub-doses of eCG. In experiment 1, chromatographic studies by reversed-phase HPLC (RP-HPLC) and by molecular exclusion (HPSEC) will be used to characterize identity and purity of three commercial products of eCG in comparison to pure eCG (Sigma) and international standard eCG (NZY-01). The biological activity of each eCG product will be determined by weighting the ovaries and uterine horns of prepubertal female rats treated with a single eCG dose (10 IU). In experiment 2, TAI performance of cows treated with 0, 300, 600 and 900 IU eCG in association with a progesterone treatment to synchronize ovulation will be evaluated. Ovulation, conception and pregnancy rates, as well as multiple, twin and single calving rates will be analyzed. (AU)