7-day CO-Synch Research Articles

The use of progestins in regimens for fixed-time artificial insemination in beef cattle

Four experiments were conducted to investigate modifications to gonadotropin releasing hormone (GnRH)-based fixed-time AI protocols in beef cattle. In Experiment 1, the effect of reducing the interval from GnRH treatment to prostaglandin (PGF) was examined. Lactating beef cows ( n=111) were given 100 mg gonadorelin (GnRH) on Day 0 (start of treatment) and either 500 μg cloprostenol (PGF) on Day 6 with AI and 100 μg GnRH 60 h later, or PGF on Day 7 with AI and GnRH 48 h later (6- or 7-day Co-Synch regimens). Pregnancy rates were 32/61 (53.3%) versus 26/50 (52.0%), respectively ( P=0.96). In Experiment 2, cattle ( n=196) were synchronized with a 7-day Co-Synch regimen and received either no further treatment or a CIDR-B device (Days 0–7). Pregnancy rates were 32/71 (45.1%) versus 33/77 (42.9%) in cows ( P<0.8), and 9/23 (39.1%) versus 17/25 (68.0%) in heifers ( P<0.05). In Experiment 3, 49 beef heifers were randomly assigned to receive 12.5 mg pLH on Day 0, PGF on Day 7 and 12.5 mg of pLH on Day 9 with AI 12 h later (pLH Ovsynch), or similar treatment plus a CIDR-B device from Days 0 to 7 (pLH Ovsynch+CIDR-B), or 1 mg estradiol benzoate (EB) and 100 mg progesterone on Day 0, a CIDR-B device from Days 0 to 7 (EB/P4+CIDR-B), PGF on Day 7 (at the time of CIDR-B removal) and 1 mg i.m. EB on Day 8 with AI on Day 9 (52 h after PGF). Pregnancy rate in the EB/P4+CIDR-B group (75.0%) was higher ( P<0.04) than in the pLH Ovsynch group (37.5%); the pLH Ovsynch+CIDR-B group was intermediate (64.7%). In Experiment 4, 266 non-lactating cows were allocated to a 7-day Co-Synch protocol (Co-Synch), a 7-day Co-Synch plus 0.6 mg per head per day melengestrol acetate (MGA) from Days 0 to 6 inclusive (Co-Synch+MGA) or MGA (Days 0–6) plus 2 mg EB and 50 mg progesterone on Day 0, 500 μg PGF on Day 7, 1 mg EB on Day 8 and fixed-time AI 28 h later (EB/P4+MGA). Pregnancy rates ( P<0.25) were 44.8% (39/87; Co-Synch), 47.8% (43/90; Co-Synch+MGA), and 60.7% (54/89; EB/P4+MGA). In conclusion, a 6- or 7-day interval from GnRH to PGF in a Co-Synch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Co-Synch or Ovsynch regimen significantly improved pregnancy rates in heifers but not in cows. Progestin-based regimens that included EB consistently resulted in high pregnancy rates to fixed-time AI.

A comparison between the in vitro embryo production potential of superstimulated and non-stimulated pregnant holstein friesland cows

One-hundred-eighty crossbred beef cows and 66 crossbred beef heifers across three locations were stratified by body weight (BW), body condition score (BCS), and age (within location) to evaluate administration of follicle stimulating hormone (FSH) on Day 2 using a modified 7-day CO-Synch plus CIDR® protocol (Day 0 = CIDR insertion) with timed-artificial insemination (TAI) at 72 h (cows) or 54 h (heifers) following CIDR removal. Estrous response following CIDR removal was determined using an Estrotect patch and TAI and final pregnancy rates were determined by transrectal ultrasonography 42–45 days following TAI and ≥45 days following removal of clean-up bulls. Estrous response rate, TAI and final pregnancy rates for cows were not affected (P ≥ 0.65) by treatment. Cows that exhibited estrus had greater (P < 0.01) TAI pregnancy rate (66%) than cows not exhibiting estrus (38%). There was an estrous response by postpartum length interaction (P = 0.02) where cows exhibiting estrus and ≥55 days postpartum had greater TAI pregnancy rates (75%) compared to cows not exhibiting estrus and <55 days postpartum (39%) or ≥55 days postpartum (28%). For heifers, timed AI (P = 0.46) and final pregnancy rates (P = 0.45) were similar across treatments and estrous response had no effect (P = 0.30) on TAI pregnancy rates. In conclusion, the addition of FSH to the CO-Synch plus CIDR estrous synchronization protocol did not increase TAI pregnancy rates in beef cows or heifers. However, a positive estrous response to the synchronization protocol was associated with increased TAI pregnancy rates in cows.