Comparison of Two Alternate Prostaglandin F2α Products in Yearling Beef Heifers

Yearling, Angus-based heifers managed at two locations were utilized to evaluate the efficacy of 2 alternate prostaglandin F_2α (PG; Lutalyse vs. Lutalyse HighCon) products. Heifers at location 1 (n = 100; 340 ± 3 kg; L1) were managed at West Central Research and Extension Center near North Platte, NE. The second location was the Kelly Ranch, near Sutherland, NE (n = 90; 326 ± 4 kg; L2). All females were offered 0.5 mg/hd melengestrol acetate for 14 d. On d 33, heifers received either 5 ml i.m. Lutalyse (5 mg/ml dinoprost tromethamine; LL) or 2 ml s.c. Lutalyse HighCon (12.5 mg/ml dinoprost tromethamine; HC). Estrus detection aids, or patches, were applied at PG injection. Heifers were AI 12 h after detection of estrus. Heifers not expressing estrus at L1 were given a second PG injection 6 d after initial injection and placed with bulls. At L2, heifers not expressing estrus were AI at 96 h post PG and given 2 ml i.m. Factrel (50 mcg/ml gonadorelin hydrochloride). Bulls were placed with AI heifers 10 d after last AI for 60 and 40 d; L1 and L2, respectively. Percentage of heifers exhibiting estrus during the estrus detection period was similar (P = 0.40) between treatments (82 vs. 87 ± 4%; LL, HC). Timing of estrus was also similar (P ≥ 0.15) with the percentage of heifers exhibiting estrus ≤ 60 h after PG (48 vs. 59 ± 5%; LL, HC), at 72 h (22 vs. 16 ± 4%; LL, HC) and ≤ 72 h (70 vs. 75 ± 5%; LL, HC). Heifer BW at first pregnancy diagnosis was 386 and 397 ± 4 kg; L1 and, L2, respectively. Pregnancy was diagnosed via ultrasonography 51 and 57 d after initial PG injection for L1 and L2, respectively. Pregnancy by AI was similar (P = 0.62; 60 vs. 65 ± 5%; LL, HC), as was final pregnancy rate (P = 0.11; 93 vs. 98 ± 3%; LL, HC), which was determined 78 and 50 d after initial pregnancy diagnosis for L1 and, L2, respectively. Heifer BW at second pregnancy diagnosis was 421 and 427 ± 14 kg for L1 and L2, respectively. Treatment did not influence (P > 0.33) final BW or ADG. In summary, the two concentrations and corresponding administration routes of PG were similar in efficacy in synchronizing estrus in yearling beef heifers.