Luteal function and reproductive response in suckled beef cows after metestrus administration of a Norgestomet implant and injection of estradiol valerate with various dosages of injectable Norgestomet

• Published in: Journal of animal science Vol. 70; no. 5; p. 1352
• Main Authors: Fanning, M D, Spitzer, J C, Burns, G L, Plyler, B B
• Format: Journal Article
• Language: English
• Published: United States 01.05.1992
• Subjects: Animals; beef cattle; blood serum; bovin de boucherie; Cattle - physiology; ciclo estral; corps jaune; corpus luteum; Corpus Luteum - drug effects; Corpus Luteum - physiology; cows; cuerpo luteo; cycle oestral; Drug Implants; Estradiol - administration & dosage; Estradiol - analogs & derivatives; Estradiol - pharmacology; estrogenos; Estrogens, Conjugated (USP) - administration & dosage; Estrogens, Conjugated (USP) - pharmacology; Estrus - drug effects; Estrus Synchronization - drug effects; Female; Fertilization - drug effects; ganado de carne; Injections, Intramuscular - veterinary; Insemination, Artificial - veterinary; intervalle entre parturition; intervalo entre partos; Metestrus; oestrogene; oestrogens; oestrous cycle; oestrus synchronization; parturition interval; performance de reproduction; Pregnenediones - administration & dosage; Pregnenediones - pharmacology; progesterona; progesterone; Progesterone - blood; Progesterone Congeners - administration & dosage; Progesterone Congeners - pharmacology; Reproduction - drug effects; reproductive performance; reproductividad; serum sanguin; sincronizacion del celo; suero sanguineo; synchronisation de l' oestrus; vaca; vache
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/1992.7051352x

In an experiment replicated over 2 yr, 149 suckled beef cows were administered Syncro-Mate-B (SMB), a 6-mg Norgestomet (NOR) ear implant (in situ 9 d) in conjunction with an i.m. injection of 5 mg of estradiol valerate (EV), and either 3.0, 4.5, or 6.0 mg. of NOR, 2 d after estrus. All cows were artificially inseminated at 48 h (timed insemination; TI) after implant removal (IR) and cows were reinseminated at any estrus subsequent to 24 h of TI through 30 d. Blood samples collected before treatment, every 3 d through IR, and at TI were assayed for progesterone (P4). At TI, 44, 39, and 12% of cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively, had serum concentrations of P4 > 1 ng/mL (3.0 and 4.5 mg vs 6.0 mg, P < 0.01). Fifty-eight, 63, and 84% of cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively, exhibited a synchronized (within 5 d of IR) estrus (3.0 and 4.5 mg vs 6.0 mg P < 0.05). Pregnancy rates for the 5-d synchronized period were 38, 45, and 66% for cows treated with 3.0, 4.5 mg vs 6.0 mg of NOR, respectively (3.0 and 4.5 mg vs 6.0 mg, P < 0.05). First-service pregnancy rates were 66, 71, and 79% for cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively (P > 0.10). Syncro-Mate-B with 6.0 mg of injectable NOR resulted in fewer cows with functional CL (i.e., P4 > 1 ng/mL at TI), more cows exhibiting estrus within 5 d of IR, and a higher 5-d pregnancy rate compared with SMB with 3.0 or 4.5 mg of injectable NOR.