Comparison of pregnancy rates of lactating Holstein dairy cows following the implementation of Presynch-Ovsynch, G6G, and Double Ovsynch protocols during the cool months of the year in the Qazvin plain of Iran

Abstract

This study evaluated the effects of three protocols on the pregnancy rate of cyclic lactating Holstein cows 30 days after 18-h fixed-time artificial insemination (FTAI): Presynch-Ovsynch (PO; PGF2alpha –14 d–PGF2alpha –12 d–Ovsynch (OVS: GnRH–7 d–PGF2alpha (PG) –2d–GnRH)–18 h FTAI; n = 210), G6G (PGF2alpha –2 d–GnRH–6 d–OVS+FTAI; n = 216), and Double-Ovsynch (DO; GnRH–7 d–PGF2alpha –3 d–GnRH–7 d–OVS+FTAI; n = 226). The overall pregnancy rates 30 days post-FTAI for cows in the PO, G6G, and DO protocols were 39.5%, 41.2%, and 43.3%, respectively (P > 0.05). The highest and the lowest circulatory concentrations of progesterone were obtained in the DO and PO protocols, respectively (P < 0.01). The Double-Ovsynch protocol significantly increased the pregnancy rate in primiparous compared to multiparous cows (P = 0.04), and also compared to the PO protocol (P = 0.04). The use of PO, G6G, and DO protocols in a fixed-time insemination program for cyclic lactating cows did not result in a significant difference in the pregnancy rate 30 days post-insemination, and therefore, a protocol that costs less and is less labour-intensive should be considered.