Comparison of long-term progestin-based protocols to synchronize estrus before fixed-time artificial insemination in beef heifers.

Two experiments were conducted to compare pregnancy rates resulting from fixed-time AI (FTAI) after administration of 1 of 2 long-term controlled internal drug release (CIDR)-based protocols. Heifers were assigned to treatment by age, BW, and pubertal status. The CIDR Select-treated heifers (Exp. 1, n = 37; Exp. 2, n = 192) received a CIDR (1.38 g of progesterone) from d 0 to 14, followed by 100 µg of GnRH, intramuscularly (i.m.) 9 d after CIDR removal (d 23) and PGF(2α) (25 mg, i.m.) 7 d after GnRH treatment (d 30). Heifers assigned to the Show-Me-Synch protocol (Exp. 1, n = 40; Exp. 2, n = 200) received a CIDR from d 0 to 14, followed by PGF(2α) 16 d later (d 30). Artificial insemination was performed at 72 or 66 h after PGF(2α) treatment for the CIDR Select- and Show-Me-Synch-treated heifers, respectively, and each heifer was given GnRH (100 µg, i.m.) at the time of AI. In Exp. 1, ovaries of each heifer were examined by transrectal ultrasonography on d 23 and 30 to characterize follicular dynamics. Follicles ≥5 mm and the presence of corpora lutea were recorded. On d 25, ovaries of each heifer were examined to characterize the status of dominant follicles recorded on d 23. Heifers were fitted with HeatWatch (DDx Inc., Denver, CO) estrus-detection transmitters at PGF(2α) to characterize estrus distribution up to FTAI. The diameter of dominant follicles on d 23 at PGF(2α) and on d 30, and the estrous response after PGF(2α) treatment up to the point of FTAI did not differ between CIDR Select- and Show-Me-Synch-treated heifers. Concentrations of progesterone in serum at PGF(2α) were greater (P = 0.07) in Show-Me-Synch- than CIDR Select-treated heifers (6.0 vs. 4.8 ng/mL, respectively). Pregnancy rates of heifers resulting from FTAI did not differ (P = 0.33) between CIDR Select- and Show-Me-Synch-treated heifers (CIDR Select, 59%; Show-Me-Synch, 70%). In Exp. 2, FTAI pregnancy rates tended (P = 0.07) to be greater in Show-Me-Synch-treated (62%) than in CIDR Select-treated (51%) heifers. Pregnancy rates at the end of the breeding season did not differ (P = 0.72; CIDR Select, 85%; Show-Me-Synch, 83%) between treatments. In summary, pregnancy rates resulting from FTAI were comparable for heifers assigned to each of the 2 long-term progestin-based protocols. The reduced treatment cost and animal handling associated with administration of the Show-Me-Synch protocol offer distinct advantages over the CIDR Select protocol despite similarities in pregnancy rates resulting from FTAI.

Mallory DA ，Nash JM ，Ellersieck MR ，Smith MF ，Patterson DJ ... -  《-》

Comparison of long-term progestin-based estrus synchronization protocols in beef heifers.

Two experiments evaluated long-term progestin-based estrus-synchronization programs on the basis of potential for use in facilitating fixed-time AI in estrous cycling and prepubertal beef heifers. In Exp. 1, heifers were assigned to 1 of 2 treatments by age, BW, and estrous cyclicity status. Heifers assigned to the melengestrol acetate-PGF(2α) protocol (MGA-PG; n = 50) received MGA (0.5 mg·animal(-1)·d(-1)) in a 1.0-kg carrier from d 0 to 13 and were administered PGF(2α) (25 mg, intramuscularly) 19 d after MGA withdrawal (d 32). Heifers assigned to the Show-Me-Synch protocol (n = 49) received a controlled internal drug release (CIDR) insert (1.38 g of progesterone) from d 2 to 16 followed by PGF(2α) administration 16 d after CIDR removal (d 32). All heifers were fitted with HeatWatch estrus-detection transmitters at the time of progestin removal for continuous estrus detection through the synchronized period after PGF(2α). In Exp. 2, heifers (n = 396) were assigned to the same 2 treatments described in Exp. 1 by age, BW, and reproductive tract score. Heifers in Exp. 2, however, were fitted with HeatWatch estrus-detection transmitters at PGF(2α) to characterize estrus-distribution patterns during the synchronized period after PGF(2α). Heifers in both experiments were inseminated approximately 12 h after the onset of estrus. In Exp. 1, estrous response after PGF(2α) and mean interval to estrus after PGF(2α) did not differ between MGA-PG and Show-Me-Synch treatments (P = 0.97). The variance for interval to estrus after PGF(2α) tended (P = 0.06) to be reduced among MGA-PG-treated heifers compared with Show-Me-Synch-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In Exp. 2, estrous response after PGF(2α) was greater (P = 0.01) among Show-Me-Synch-treated heifers (92%) compared with MGA-PG-treated heifers (85%); however, mean interval to estrus after PGF(2α) did not differ (P = 0.74) between MGA-PG (57.4 ± 2.5 h) and Show-Me-Synch (56.2 ± 2.5 h) treatments. The variance for interval to estrus after PGF(2α) was reduced (P < 0.01) among Show-Me-Synch-treated vs. MGA-PG-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In summary, the Show-Me-Synch protocol compared favorably with the MGA-PG protocol on the basis of estrous response, synchrony of estrus, and resulting fertility after treatment administration.

Mallory DA ，Wilson DJ ，Busch DC ，Ellersieck MR ，Smith MF ，Patterson DJ ... -  《-》

Comparison of short-term progestin-based protocols to synchronize estrus and ovulation in postpartum beef cows.

Two experiments evaluated short-term controlled internal drug release (CIDR) insert-based protocols to synchronize estrus and ovulation and compare differences in their potential to facilitate fixed-time AI (FTAI) in postpartum beef cows. Experiment 1 was designed to compare the 7- and 5-d Select Synch + CIDR protocols on the basis of timing and synchrony of estrus after treatment. Cows assigned to the 7-d protocol (n = 59) received GnRH [100 microg intramuscularly (i.m.)] and CIDR inserts (1.38 g of progesterone) on d 0 and PGF(2alpha) (25 mg i.m.) and CIDR removal on d 7. Cows assigned to the 5-d protocol (n = 58) received GnRH and CIDR inserts on d 2, PGF(2alpha) and CIDR removal on d 7, and a second injection of PGF(2alpha) 12 h after CIDR removal. Estrus detection and AI were performed for cows assigned to each protocol during the 144-h synchronized period. There was no difference in estrous response (P = 0.85), interval to estrus (P = 0.09), or variance for interval to estrus (P = 0.75) between treatments, nor were there differences in synchronized conception or pregnancy rates resulting from AI (P = 0.85, P = 0.91, respectively). Experiment 2 was designed to compare pregnancy rates resulting from FTAI after administration of the 7- and 5-d CO-Synch + CIDR protocols. Both treatments were administered the same as in Exp. 1; however, cows assigned to the 7-d protocol were inseminated 66 h after PGF(2alpha) and CIDR removal, and cows assigned to the 5-d protocol were inseminated 72 h after the first PGF(2alpha) injection. Cows assigned to both protocols were administered GnRH (100 microg i.m.) at AI. There was no effect of treatment (P = 0.85), technician (P = 0.20), or sire (P = 0.25) on pregnancy rates resulting from FTAI. Given these observations, the 5-d protocol provides an effective alternative to the 7-d protocol for use in facilitating FTAI; however, beef producers must carefully consider the increased labor and treatment costs associated with the 5-d protocol.

Wilson DJ ，Mallory DA ，Busch DC ，Leitman NR ，Haden JK ，Schafer DJ ，Ellersieck MR ，Smith MF ，Patterson DJ ... -  《-》

Comparison of progestin-based estrus synchronization protocols before fixed-time artificial insemination on pregnancy rate in beef heifers.

The objective of the experiment was to compare pregnancy rates resulting from fixed-time AI after administration of either 1 of 2 controlled internal drug release (CIDR)-based protocols. Heifers at 3 locations (location 1, n = 78; location 2, n = 61; and location 3, n = 78) were assigned to 1 of 2 treatments within reproductive tract scores (1 = immature to 5 = cycling) by age and BW. Heifers assigned to CIDR Select received a CIDR insert (1.38 g of progesterone) from d 0 to 14 followed by GnRH (100 mug, i.m.) 9 d after CIDR removal (d 23) and PGF2alpha (PG, 25 mg, i.m.) 7 d after GnRH treatment (d 30). Heifers assigned to CO-Synch + CIDR were administered GnRH and received a CIDR insert on d 23 and PG and CIDR removal on d 30. Heifers at location 1 were fitted with a HeatWatch estrus detection system transmitter from the time of PG until 24 d after fixed-time AI to allow for continuous estrus detection. Artificial insemination was performed at predetermined fixed times for heifers in both treatments at 72 or 54 h after PG for the CIDR Select and CO-Synch + CIDR groups, respectively. All heifers were administered GnRH at the time of AI. Blood samples were collected 10 d before and immediately before treatment initiation (d 0) to determine pretreatment estrous cyclicity (progesterone > or = 0.5 ng/mL). At location 1, the estrous response during the synchronized period was greater (P = 0.06; 87 vs. 69%, respectively), and the variance for interval to estrus after PG was reduced among CIDR Select- (P < 0.01) compared with CO-Synch + CIDR-treated heifers. Fixed-time AI pregnancy rates were significantly greater (P = 0.02) after the CIDR Select protocol (62%) compared with the CO-Synch + CIDR protocol (47%). In summary, the CIDR Select protocol resulted in a greater and more synchronous estrous response and significantly greater fixed-time AI pregnancy rates compared with the CO-Synch + CIDR protocol.

Busch DC ，Wilson DJ ，Schafer DJ ，Leitman NR ，Haden JK ，Ellersieck MR ，Smith MF ，Patterson DJ ... -  《-》

Comparison of long- versus short-term CIDR-based protocols to synchronize estrus prior to fixed-time AI in postpartum beef cows.

This experiment was conducted to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) after treatment with controlled internal drug release (CIDR)-based protocols to synchronize estrus. Cows assigned to the Show-Me-Synch (n=167) protocol received a CIDR from d 0 to 14, and prostaglandin F(2α) (PGF(2α)) on d 30. Cows assigned to 7-d CO-Synch+CIDR (n=177) received a CIDR and gonadotropin releasing hormone (GnRH) on d 23. On d 30, CIDRs were removed and PGF(2α) was administered. Blood sampling occurred on d -10 and 0 of treatment to determine estrous cyclicity status (progesterone ≥0.5 ng/mL estrous cycling). Treatments were balanced on age, DPP and BCS. Estrous detection was performed using HeatWatch from PGF(2α) to FTAI. Artificial insemination was performed at predetermined fixed times (72 h, Show-Me-Synch; 66h, 7-d CO-Synch+CIDR) and all cows were administered GnRH at FTAI. This experiment was conducted over a two year period; no differences were found between years so the data were pooled for further analysis. Pregnancy rate resulting from FTAI did not differ (P>0.10) between technicians or AI sires. Pregnancy rate resulting from FTAI was similar between treatments (P=0.20); however, cows that exhibited estrus prior to FTAI had a higher pregnancy rate (P<0.01) than for those that did not. Pregnancy rate at the end of the breeding period was similar between treatments (P=0.28). In summary, FTAI pregnancy rates were similar among postpartum beef cows following treatment with either a short- or long-term CIDR-based estrous synchronization protocol.

Nash JM ，Mallory DA ，Ellersieck MR ，Poock SE ，Smith MF ，Patterson DJ ... -  《-》