Synchronisation of oestrus in dairy cows using prostaglandin F2α, gonadotrophin-releasing hormone, and oestradiol cypionate

An oestrous synchronisation protocol was developed for use in lactating dairy cows using PGF2α, GnRH, and oestradiol cypionate (ECP). In experiment 1, lactating dairy cows received two injections of PGF2α (on days 0 and 11) (PP; n=10) or two injections of PGF2α (days 0 and 11) and 100 μg of GnRH on day 3 (PGP; n=10). In experiment 2, cows were treated with PGP (n=7), or PGP and 1 mg of ECP at the same time (PGPE0; n=7) or 1 day after the second PGF2α injection (PGPE1; n=7). In experiment 3, 101 lactating dairy cows in a commercial herd were assigned to one of three treatments; PP, PGP, or PGPE1. Follicular growth was measured by ultrasound in experiments 1 and 2. Every cow (experiments 1, 2, and 3) was blood sampled at selected intervals for progesterone and oestradiol assays and inseminated at oestrus. In experiment 1, a higher percentage of GnRH-treated cows ovulated after the first PGF2α injection (90% versus 50%; P<0.05). The GnRH-treated cows tended to have a larger dominant follicle present at the time of the second PGF2α injection (16.5+/-0.5 mm versus 15.0±0.7 mm; P<0.10). The percentage of cows that ovulated after the second PGF2α injection was similar (60%). In experiment 2, cows treated with ECP had higher peak preovulatory concentrations of oestradiol in plasma (6.99+/-0.63 versus 3.63+/-0.63; P<0.01) following the second PGF2α injection and a higher percentage ovulated (86% versus 43%; P<0.05). A higher percentage of PGPE1-treated cows in experiment 3 were observed in standing oestrus and ovulated after the second PGF2α injection (standing oestrus, 26.4, 34.3, and 62.6%, P<0.01; ovulated, 56, 63, and 78%, P<0.05; PP, PGP, and PGPE1, respectively). In conclusion, the PGP protocol increased the number of cows that ovulated after the first PGF2α injection and produced a more mature dominant follicle at the time of the second PGF2α injection. Adding ECP to PGP (PGPE1) enhanced the expression of oestrus and increased ovulation percentage. The combination of PGP and ECP is potentially a new method to routinely synchronise oestrus and ovulation in dairy cows.