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.
The effectiveness of two estrus-detection methods (visual observation and radiotelemetric, pressure-sensitive, rump-mounted devices) was compared in peripubertal, crossbred yearling beef heifers. Heifers (n = 50) were fitted with a pressure-sensitive device affixed to their rumps to which a battery-operated radio transmitter was connected. Activation of the sensor sent a radiotelemetric signal to a microcomputer via a fixed radio antenna. Heifer identification, date, time, and duration of standing events were recorded. Estrus was synchronized by feeding melengestrol acetate (MGA) for 14 d and then injecting PGF2 alpha 17 d after the last daily dose of MGA. Following the injection of PGF2 alpha, heifers were observed visually for signs of estrus at 0730 and 1630 (45 min each). Estrus was detected in 41 of 49 heifers (one lost the device) by visual observation and(or) the radiotelemetric device. Number of standing events during estrus, determined by the radiotelemetric device, averaged 50.1 +/- 6.4 per heifer, with the duration of estrus ranging from 2.6 to 26.2 h (average = 14 +/- .8 h). Visual observation failed to detect 11 of 41 heifers (37%) that were detected by the radiotelemetric device. Heifers with fewer standing events (19.3 vs 60.5; P < .001) and estrus of shorter duration (8.4 vs 15.6 h; P < .001) were those not identified by visual observation. Based on intervals between the first detected standing event of estrus and time of insemination, a wide window of fertility seems to exist in some heifers. Radiotelemetric devices were useful in identifying a greater (P < .05) proportion (100%) of heifers in estrus (increased efficiency) compared with visual observation (73%). However, accuracy of both methods was similar.
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