Our hypothesis was to develop a timed-AI protocol with good fertility but reduced cost and labour under commercial conditions. Heifers were divided two group and first group (n=19) received two injections of PGF2a 14 days apart. GnRH was injected 48 h after the second PGF2a injection and heifers were inseminated 14-16 h following GnRH (day 0; PPG group). This synchronization regimen was compared with a widely used progesterone-based protocol.

In the implant group (IMP group; n=29), a norgestomet ear implant was used and estradiol valerate plus norgestomet injected (i.m.; day 0). On Day 8, heifers received PGF2a and implant was removed on day 9. Heifers were inseminated 48 h after implant removal. Pregnancy diagnosis was performed by real-time ultrasound between day 31 and 38. Eleven of 19 heifers in the PPG group were pregnant (57.9%) compared to 14 of29 heifers in the IMP group (48.2%; P>0.05 Chi-squared) Thus, the timed-AI protocol utilizing two doses of PGF2a and GnRH resulted in acceptable pregnancy rates compared to the progesterone-based protocol which was more labour intensive.