Abstract

QUEZADA CASASOLA, Andrés et al. Comparación de dos protocolos de sincronización del estro en vaquillas de carne con distintas calificaciones de tracto reproductivo . INCI [online]. 2004, vol.29, n.11, pp.638-642. ISSN 0378-1844.

To compare the effect of two estrus synchronization protocols (MGA^®+PGF2a and Crestar^®) in beef heifers, 28 animals 15-18 months of age were classified according to their reproductive tract scoring (RTS) in A: RTS 2-3 (n=14), and B: RTS 4-5 (n=14). A and B were subdivided forming four groups of seven heifers each for the application of: MGA^®+PGF2a with RTS A (1A) or B (1B); Crestar^® with RTS A (2A) or B (2B). The first protocol included MGA^® for 14d followed by PGF2a i.m. 19d afterwards. The second included 5mg of estradiol valerate and 3mg of norgestomet i.m., along with an implant with 3mg s.c. of norgestomet for 9d. When both protocols ended, heifers were artificially inseminated at detected estrus. Variables evaluated were estrus presentation in response to protocol, time from end of protocol to onset of estrus, pregnancy rate at first synchronized estrus, pregnancy rate at the end of programmed breeding season, and the ability to induce ovarian activity in non-cycling heifers. Statistical analyses consisted of "t" student, Chi-square and Exact Fisher tests. Group 1B showed higher (P<0.10) estrous response rate (100%) than all other groups (85.7%). Time from end of protocol to onset of estrus was shorter (P<0.05) in group 2B (34 ±9.03h) than in the other groups; however, it was higher (P<0.05) for protocol MGA^®+PGF2a (69.2 ±14.8h) than Crestar^® (49 ±31.7h). The protocol MGA^®+PGF2a had higher (P<0.05) induction of ovarian activity in non-cycling heifers than Crestar^® (100 vs 14.2%). Both protocols presented similar (P>0.10) pregnancy rate at first synchronized estrus (61.5 and 58.3% for MGA^®+PGF2a and Crestar^® respectively); however, group 1B (85.7%) had a higher rate (P<0.10) than groups 1A (33%), 2B (66.6%) and 2A (50%). Pregnancy rate at the end of programmed breeding season was similar (P>0.10) in all groups. It is concluded that protocol MGA^®+PGF2a had a higher capacity to initiate ovarian activity in non-cycling heifers, and can be used more efficiently in artificial insemination programs in animals with RTS of 4 or 5

Keywords : Ganado de Carne; Inducción del Estro; Porcentaje de Gestación; Vaquillas de Reemplazo.