RESUMEN
Mean estrous response rate (%ERR) and pregnancy/AI percentages (%P/AI) were determined after imposing split-time AI (STAI) and fixed time AI (FTAI) following 14-d controlled internal drug release (CIDR)+PGF2α or 5-d Select Synchâ¯+â¯CIDR regimens. In Experiment 1, 1152 heifers (five locations) were randomly assigned to 14- or 5-d and to 54â¯+â¯74- or 64â¯+â¯84-h STAI treatment combinations. Estrous detection patches were affixed at PGF2α administration (19 day after- and on day 5 at- CIDR removal for 14- and 5-d regimens, respectively), assessed at 54- or 64-h and again at 74- or 84-h after PGF2α. Heifers determined to be in estrus at respective times were inseminated and non-estrous heifers at 74- or 84-h were given GnRH and inseminated concomitantly. The %ERR between 54â¯+â¯74- and 64â¯+â¯84-h STAI combinations differed (73.2 % and 78.8 %, respectively; Pâ¯<â¯0.05), but %P/AI did not. In Experiment 2, 2014 heifers (eight locations) were randomly assigned to 14- or 5-d regimens and were inseminated split-time (64+84-h combination, similar to Experiment 1) or at fixed time (72- or 56-h after PGF2α for 14- or 5-d regimens, respectively). There were differences (Pâ¯<â¯0.01) between STAI and FTAI treatments for %ERR (81.3 % and 64.4 %) and %P/AI (61.2 % and 55.4 %). Estrous synchronization regimen by AI treatment interaction (Pâ¯<â¯0.05) showed that the %ERR were 79.8 %, 82.6 %, 66.2 % and 62.8 % and the %P/AI were 58.9 %, 63.4 %, 56.5 % and 56.5 % (for 14-d/STAI, 5-d/STAI, 14-d/FTAI and 5-d/FTAI, respectively). In conclusion, the 5-d CIDR with 64+84-h STAI combination was the most effective because of the greater %P/AI when this regimen was imposed.
Asunto(s)
Bovinos/fisiología , Dinoprost/farmacología , Sincronización del Estro/métodos , Progesterona/farmacología , Administración Intravaginal , Animales , Dinoprost/administración & dosificación , Esquema de Medicación , Femenino , Inseminación Artificial/veterinaria , Embarazo , Índice de Embarazo , Progesterona/administración & dosificación , ProgestinasRESUMEN
Objectives were to compare pregnancy percentages per embryo transfer (P/ET) in recipient beef cows following twice daily compared with split-time estrous detection and to determine associations of dominant follicle diameter, CL volume and progesterone concentrations. All cows (nâ¯=â¯695) were treated to synchronize time of estrus among cows using a CIDRâ¯+â¯Select-Synch treatment regimen and randomly assigned to twice-daily or split-time estrous detection (CS-DEET or CS-SEET, respectively). Cows in the CS-DEET group were observed twice daily (eight times) for estrus until 96â¯h after the time of PGF2α administration, whereas cows in the CS-SEET group were observed twice (64 and 84â¯h after PGF2α). In 280 recipient cows, blood sampling (for progesterone) and ultrasonographic assessment of dominant follicle diameter were conducted 48â¯h after the time of PGF2α administration. At 7 d after estrus, the CL was imaged and there was transfer of a frozen-thawed embryo into cows with a CLâ¯≥â¯1.5â¯cm. There were positive correlations between follicle diameter and CL volume (rs = 0.827; Pâ¯<â¯0.001) and CL volume and progesterone concentration (rsâ¯=â¯0.680; Pâ¯<â¯0.001). Progesterone and CL volume differed between cows in CS-SEET and CS-DEET groups Pâ¯<â¯0.05), however, percentage P/ET for cows in the CS-SEET and CS-DEET groups did not differ (Pâ¯>â¯0.1). Dominant follicle diameter, CL volume and progesterone concentrations were greater in pregnant compared with nonpregnant cows. In conclusion, percentage P/ET did not differ when there was twice daily and split-time estrous detection highlighting the value of this approach in beef enterprises.