Aplicación del protocolo Select-Synch y su efecto sobre la concentración de progesterona plasmática en vacas multíparas ubicadas en el llano central venezolano

To compare plasmatic progesterone concentrations changes during the Select-synch protocol application, 32 multiparous cows was evaluated during dry season. P4 concentration was measured during the protocol, at heat time and 21 days after insemination. Were included cows with ovarian activity (follicles =3mm or CL´s) with BC 3.6±0.1 (scale 1-5). The synchronization protocol consisted in an 100 ?g of GnRH i.m. application, followed 7 d after of 25 mg of PGF2alfa (i.m.), with detection of heat (06:00-18:00 h) then to be insemination. Fifty nine (59.4%) of the cows (19/32) presented heat 5.1±0.2 day after PGF2alfa application. The P4 concentration was significance between days (p<0.01) decreeing from the day of application with GnRH (12.4+1.0 ng/mL) to day 3 of the protocol (8.1+0.9 ng/mL), then increased until the application day of PGF2alfa (15.0+1.1ng/mL), and descended progressively until the smaller concentration of P4 the heat day (0.7+0.1 ng/mL). The 21 day post-insemination, P4 plasmatic concentration was greater (9.3+0.7 ng/mL; p<0.01) in pregnant cows (n=14), than in open cows (n=6; 1.1+0.1 ng/mL). The P4 concentrations in the heat day, give an idea of the answer to the synchronization protocol, whereas the P4 concentration in day 21 post-insemination, has predictive value in pregnant and/or open cows.