Programs for fixed-time artificial insemination in South American beef cattle

Abstract

Fixed-time artificial insemination (FTAI) has been widely applied in South America within the last 20 years for the genetic improvement of commercial beef herds. Most FTAI treatments for beef cattle used in South America are based on the use of progesterone (P4) releasing devices and estradiol to synchronize follicle wave emergence, with pregnancies per AI (P/AI) ranging from 40 to 60%. More recent protocols focusing on extending the interval from device removal to FTAI (i.e. increasing the growing period of the ovulatory follicle) have been reported to improve P/AI in beef cattle. These new protocols and the more traditional FTAI protocols have also been adapted for use with sexed-sorted semen with acceptable P/AI in beef cattle. Finally, color-flow Doppler ultrasonography has been incorporated recently to determine the vascularity of the CL and thereby detect pregnancy as early as Day 22 after the first AI for re- synchronization of ovulation for a second FTAI in non- pregnant animals. In summary, FTAI protocols have facilitated the widespread application of AI in South American beef cattle by allowing for the insemination and re-insemination of herds during a defined breeding season, without the necessity of clean up bulls to achieve high pregnancy rates.

Keywords: color-flow Doppler ultrasonography; proestrus length; sexed-sorted semen..

Figure 1. Two protocols for FTAI in beef cattle using GnRH. (A) 5-day Cosynch+P4 protocol. The interval from P4 device removal to FTAI is 66-72 h in heifers and 72 h in cows. If tail-paint or patches are used for estrus detection, FTAI begins at 60 h in all heifers with altered paint and those with the paint intact receive GnRH and are FTAI at 72 h. A second PGF₂α administered at the same time of the device removal or 6 to 12 h later is recommended in cows and 400 IU of eCG may also be given in cows in postpartum anestrus. (B) Modified 5-day GnRH+P4 protocol. GnRH is not administered at P4-device insertion and only one PGF₂α is required on Day 5. The recommended intervals from P4 device removal to FTAI are similar to those described previously.

Figure 2. Estradiol/P4-based protocol with prolonged proestrus (J-Synch) in beef heifers. For FTAI without estrus detection, heifers receive GnRH and are inseminated 66-72 h after P4-device removal. If tail-paint or patches are used for estrus detection, FTAI begins at 60 h in all heifers with altered paint and those with the paint intact receive GnRH and are FTAI at 72 h. eCG (300 IU in heifers and 400 IU in cows) may also be given in those animals in anestrus.

Figure 3. Conventional estradiol/P4-based protocol for FTAI with sexed-sorted semen. Tail-paint or patches are used to detect those animals in estrus 60 h after P4-device removal. Animals in estrus by 60 h are inseminated with sexed-sorted semen whereas those animals not in estrus by 60 h receive GnRH and are inseminated at the same time with sexed-sorted or non-sexed semen.

Figure 4. Alternative estradiol/P4 based protocol with prolonged proestrus for FTAI beef heifers with sexed-sorted semen. Tail-paint or patches are used to detect those heifers in estrus at 60 and 72 h after P4-device removal. Heifers in estrus at 60 and 72 h are inseminated at 72 h with sexed-sorted semen. Heifers not in estrus by 72 h receive GnRH and are inseminated at 84 h with sexed sorted or non-sexed semen.