Synchronizing estrus and(or) ovulation in beef cows after combinations of GnRH, norgestomet, and prostaglandin F2alpha with or without timed insemination.

Abstract

Three experiments were conducted to induce estrus and(or) ovulation in 1,590 suckled beef cows at the beginning of a spring breeding season. In Exp. 1, 890 cows at three locations were allotted to three treatments: 1) GnRH on d -7 + prostaglandin F2alpha (PGF2alpha) on d 0 (Select Synch); 2) GnRH on d -7 + PGF2alpha on d 0 (first day of the breeding season) plus a norgestomet implant (NORG) between d -7 and 0 (Select Synch + NORG); or 3) two injections of PGF2alpha given 14 d apart (2xPGF2alpha). More (P < 0.05) cycling cows were detected to have been in estrus after both treatments that included GnRH, whereas, among noncycling cows, the addition of norgestomet further increased (P < 0.05) the proportion in estrus. Pregnancy rates were greater (P < 0.01) among noncycling cows after treatments that included GnRH. For cows that calved >60 d before the onset of the breeding season, conception rates were greater (P < 0.01) than those that calved < or =60 d regardless of treatment, whereas days postpartum had no effect on rates of detected estrus. When body condition scores were < or =4 compared with >4, rates of detected estrus (P < 0.05) and conception (P = 0.07) were increased. In Exp. 2, 164 cows were treated with the Select Synch + NORG treatment and were inseminated either after estrus or at 16 h after a second GnRH injection (given 48 h after PGF2alpha). Conception and pregnancy rates tended (P = 0.08) to be or were less (P < 0.05), respectively, for noncycling cows inseminated by appointment, but pregnancy rates exceeded 53% in both protocols. In Exp. 3, 536 cows at three locations were treated with the Select Synch protocol as in Exp. 1 and inseminated either: 1) after detected estrus (Select Synch); 2) at 54 h after PGF2alpha when a second GnRH injection also was administered (Cosynch); or 3) after detected estrus until 54 h, or in the absence of estrus, at 54 h plus a second GnRH injection (Select Synch + Cosynch). Conception rates were reduced (P < 0.01) in cows that were inseminated by appointment. An interaction of AI protocol and cycling status occurred (P = 0.05) for pregnancy rates with differing results for cycling and noncycling cows. Across experiments, variable proportions of cows at various locations (21 to 78%) were cycling before the breeding season. With the GnRH or GnRH + NORG treatments, ovulation was induced in some noncycling cows. Conception rates were normal and pregnancy rates were greater than those after a PGF2alpha program, particularly when inseminations occurred after detected estrus.

Estrus Induction and Fertility Rates in Response to Exogenous Hormonal Administration in Postpartum Anestrous and Subestrus Bovines and Buffaloes

“…The reason for commencement of estrus in some (n=5) cattle in control Gp Ib that failed to conceive could not be ascertained; however, it might have been due to repeated rectal ovarian massage [14]. Following hormonal treatment of the true anestrous cattle, a relatively lower FSCR (44% vs 49-60%) and OCR (48% vs 63%) was observed in the present study compared with previous studies [1,29], this might be attributable to poor BCS [8,33]; on the other hand, the conception rates of the buffaloes were comparable to the previous studies [23,27].…”

“…A combination of controlled internal drug release (CIDR) for 7 days followed by an injection of 1 mg estradiol benzoate [11] and, more recently, a first injection of gonadotrophin releasing hormone (GnRH) followed by prostaglandin F 2α (PGF 2α ) on day 7 and a second injection of GnRH on day 9 (day 0, GnRH; day 7, PGF 2α ; day 9, GnRH) have been adopted in cattle [33]. Treatment of bovines suffering from subestrus has mainly focused on the use of natural or synthetic PGF 2α , [17,23,31].…”

Gonadotropin-releasing hormone increased pregnancy risk in suckled beef cows not detected in estrus and subjected to a split-time artificial insemination program12

“…Postpartum suckled cows that are anestrous at the onset of TAI programs seem to display estrus earlier than their estrus-cycling herd mates (Geary et al, 2000;Stevenson et al, 2000;Busch et al, 2008). In contrast, previous estrus cycle status of the sampled subpopulation of cows in the present study did not influence the proportion of cycling and noncycling cows detected in estrus by 65 h after PGF 2α .…”

Altered progesterone concentrations by hormonal manipulations before a fixed-time artificial insemination CO-Synch + CIDR program in suckled beef cows

“…Addition of a progestin to the protocol improved the pregnancy response in anestrous cows [19,20]. These studies also produced pregnancy outcomes in anestrous cows that exceeded 50% at TAI; however, variability in follicle size and maturity at AI [7,10] probably limited the pregnancy response to TAI programs.…”

“…Prebreeding progesterone exposure also altered the subsequent pregnancy outcome, particularly when anestrous cows were compared with cycling cows [19,20] Nevertheless, the cycling cows responded to the PrePG and PrePGG injections in predictable fashion. In Experiment 1, the proportion of cows with luteolysis was two-fold greater and the number of cows with a new CL on study Day 10 was nearly two-fold greater than in the control.…”