Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F₂α, and progesterone

• Published in: Journal of animal science Vol. 84; no. 11; pp. 3000 - 3009
• Main Authors: Lamb, G.C, Larson, J.E, Geary, T.W, Stevenson, J.S, Johnson, S.K, Day, M.L, Ansotegui, R.P, Kesler, D.J, DeJarnette, J.M, Landblom, D.G
• Format: Journal Article
• Language: English
• Published: Savoy, IL American Society of Animal Science 2006
• Subjects: Animal productions; artificial insemination; beef cattle; Biological and medical sciences; controlled internal drug release devices; estrous cycle; estrus; estrus detection; estrus synchronization; fecundity; Food industries; Fundamental and applied biological sciences. Psychology; gonadotropin-releasing hormone; heifers; Meat and meat product industries; ovarian development; pregnancy diagnosis; pregnancy rate; progesterone; prostaglandins; replacement animals; Terrestrial animal productions; timed artificial insemination; Vertebrates; Hormone; Estrus; Bovine; Meat product; Ox; Replacement; Gonadotropin; Synchronization; Prostaglandin F2α; Reproduction; Vertebrata; Mammalia; Artificial insemination; Heifer; Artiodactyla; Progesterone; Beef; timed artificial insemination; Ungulata; beef heifer
• ISSN: 0021-8812; 1525-3163

We evaluated whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or detection of estrus and AI plus a clean-up TAI for heifers not detected in estrus, and whether adding an injection of GnRH at controlled internal drug release (CIDR) insertion would enhance fertility in CIDR-based protocols. Estrus in 2,075 replacement beef heifers at 12 locations was synchronized, and AI was preceded by 1 of 4 treatments arranged as a 2 x 2 factorial design: 1) Estrus detection + TAI (ETAI) (n = 516): CIDR for 7 d plus 25 mg of prostaglandin F₂α (PG) at CIDR insert removal, followed by detection of estrus for 72 h and AI for 84 h after PG (heifers not detected in estrus by 84 h received 100 μg of GnRH and TAI); 2) G+ETAI (n = 503): ETAI plus 100 μg GnRH at CIDR insertion; 3) Fixed-time AI (FTAI) (n = 525): CIDR for 7 d plus 25 mg of PG at CIDR removal, followed in 60 h by a second injection of GnRH and TAI; 4) G+FTAI (n = 531): FTAI plus 100 μg of GnRH at CIDR insertion. Blood samples were collected (d -17 and -7, relative to PG) to determine ovarian status. For heifers in ETAI and G+ETAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed according to the a.m.-p.m. rule. Pregnancy was diagnosed by transrectal ultrasonography. The percentage of heifers exhibiting ovarian cyclic activity at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38 to 74%. Pregnancy rates were 54.7, 57.5, 49.3, and 53.1% for ETAI, G+ETAI, FTAI, and G+FTAI treatments, respectively. Although pregnancy rates were similar among treatments, a tendency (P = 0.065) occurred for pregnancy rates in the G+ETAI treatment to be greater than in the FTAI treatment. We concluded that the G+FTAI protocol yielded pregnancy rates similar to protocols that combine estrus detection and TAI. Further, the G+FTAI protocol produced the most consistent pregnancy rates among locations and eliminated the necessity for detection of estrus when inseminating replacement beef heifers.