| Abstrakt: |
Sexed semen artificial insemination is a reproductive technology that allows producers to enhance genetics through use of superior sires, control gender of offspring, and increase profitability. However, sexed semen practices have yet to be widely used within the beef cattle industry due to reduced conception rates, decreased sperm cell numbers in comparison with conventional semen, and increased costs. The objective of this study was to determine the effects of time of estrus, time of insemination, sire, weight, and age on pregnancy rates within a fixed-time artificial insemination (FTAI) protocol using two fixed-time inseminations and female sex-sorted semen from three sires (SexedULTRA 4M, STGenetics, Navasota, TX). Multiparous commercial beef cows (n = 130) were randomized into synchronization protocol and sire treatments by age, body condition score (BCS), and days post-partum at the University of Arkansas Savoy Research Complex in Fayetteville, AR. Synchronization treatments included the 8&6 Synch protocol using two FTAI times: 66 h or 72 h post-CIDR removal. Each synchronization treatment used a controlled internal drug releasing device (Eazi-breed CIDR; 1.38g progesterone, Zoetis, Kalamazoo, MI) inserted intravaginally -14 d of the protocol simultaneous to administration of prostaglandin F2α (PGF; 25mg dinoprost tromethamine; Lutalyse HighCon, Zoetis). In both treatments (66 h) and (72 h), gonadotropin-releasing hormone (GnRH; 100µg gonadorelin; Factrel, Zoetis) was administered on d -6. Each treatment was then administered PGF simultaneous to CIDR removal on 0 d, 66 ± 2 h prior to FTAI within the 66 h treatment, and 72 ± 2 h prior to FTAI within the 72 h treatment and final administration of GnRH. Standing heat (estrus) was visually detected every 3 h for 30 min intervals between the time of CIDR removal and FTAI. Estrotect patches (Rockway Inc., Spring Valley, WI) were used in conjunction with visual detection. Time of estrus was signified as time of solid footing while standing to be mounted in combination with presenting a patch score of 4 (>75% color rubbed off). Pregnancy rates (PR) were determined via ultrasound 42 ± 1 d after FTAI. PR were analyzed by time of estrus (TE), fixed-time insemination protocol (TRT), age, and body weight using the GLIMMIX procedure on SAS 9.4 (SAS Institute Inc., Cary, NC). There were no significant effects on PR by age or body weight. TE (P = 0.30) and TRT (P = 0.28) were also found to be non-significant. TE was divided into 4 time groups at < 11 h, 11.01-22 h, >22.01 h (hours prior to FTAI), or non-estrual; resulting in PR of 53 %, 74 %, 50 %, and 64 % respectively. In conclusion, data collected suggests acceptable pregnancy rates may be achieved within a fixed-time artificial insemination protocol using sexed semen regardless of age, weight, synchronization treatment, or time of estrus. [ABSTRACT FROM AUTHOR] |
