A self-determining control circuit is configured to assume one of several states depending upon the interconnections of its input and output terminals. The self-determining circuit is enabled to sense which, if any, of its input and output have been interconnected and assume its proper state of operation. For example, a self-determining integrated circuit may have four input terminals (e.g., terminals 1, 2, 3, 4 ) and four output terminals (e.g., terminals A, B, C, D). The circuit may sense that a particular input terminal is directly connected with a particular output terminal (e.g., input terminal 2 is shorted to output terminal D) and operate under one set of parameters. If, however, the control circuit senses that a different set of terminals are interconnected (e.g., input terminal 4 with output terminal B), then the control circuit may operation under a different set of parameters. Similarly, if the control circuit senses that none of the terminals are interconnected (or connected to a supply potential), then it may operate under yet a different set of parameters.

This study evaluated ovarian and estrous responses as affected by day of the estrous cycle at initiation of treatment among cows synchronized with the Select Synch protocol. Fifty-six suckled Hereford x Red Angus multiparous cows were fitted with HeatWatch® electronic estrous detection monitors 22 d before initiation of treatment. Thirty-two percent of cows were not detected in estrus during this 22-d period, and were classified as anestrus. Treatment included an injection of Gonadotropin releasing hormone (GnRH; 100 μg) on d 7, followed by an injection of Prostaglandin F2α (PGF2α; 25 mg) on d 0. Ovaries of cows were scanned daily via ultrasound from d 12 until the time of insemination to evaluate follicular and luteal response to the GnRH and PGF2α injections. Cows were visually observed for signs of estrus twice daily from d 0 to d 5 for approximately 2h to compare visual detection of estrus with electronic detection. There was no difference (P>0.5) in the percentage of cows detected in estrus between visual (85%) and electronic (88%) observation. Ovarian and estrous responses to the GnRH and PGF2α injections were dependent on day of the estrous cycle when the protocol was initiated. Ovulation resulting in formation of a new corpus luteum (CL) and follicular turnover occurred following the injection of GnRH in 66 and 70% of cows, respectively. Only 14% of cows that were between d 15 and 17 of their estrous cycle responded to either GnRH or PGF2α administration. Additionally, these cows exhibited estrus 11 ± 19h (mean ± SD) before injection of PGF2α. Anestrous cows exhibited estrus earlier (P<0.05) than cyclic cows (40.2 ± 16h and 56.3 ± 39 h, respectively). Synchronized pregnancy rate was 71% for the 5 d breeding period, and included a 61% pregnancy rate among anestrous cows. We conclude that the Select Synch protocol is capable of synchronizing estrus among the majority of cows in a herd, and we emphasize that accurate estrous detection beginning 24 to 30h before the PGF2α injection is important.

We compared pregnancy rates of beef cows subjected to the traditional Syncro-Mate-B protocol or the new Ovsynch protocol and timed insemination. Multiparous Angus cows (n = 436) were stratified by age, postpartum interval, and AI sire and were randomly divided into two treatment groups for synchronization of estrus/ovulation. Approximately half of the cows (n = 216) received the traditional Syncro-Mate-B protocol with 48-h calf removal from the time of implant removal until breeding. The remaining cows (n = 220) received the Ovsynch protocol, which consists of an injection of GnRH (100 microg) on d -10, an injection of PGF2alpha (25 mg) and 48-h calf removal on d -3, another injection of GnRH and calf return on d -1, and timed insemination 24 h later (d 0). Blood samples were collected from all cows before treatment to identify anestrous and cyclic females. Pregnancy rates were higher (P < .025) for Ovsynch-treated cows (54%) than for Syncro-Mate-B-treated cows (42%). Pregnancy rates of cyclic Ovsynch-treated cows (59%) were higher (P < .005) than pregnancy rates of cyclic Syncro-Mate-B-treated cows (38%). Pregnancy rates of anestrous cows also tended to favor synchronization with the Ovsynch protocol. From these data, we conclude that the Ovsynch protocol is capable of inducing a fertile ovulation in cyclic and anestrous beef cows and that pregnancy rates to a timed insemination are higher than those obtained with synchronization of estrus using Syncro-Mate-B.