Effects of gonadotropin-releasing hormone at initiation of the 5-d timed artificial insemination (AI) program and timing of induction of ovulation relative to AI on ovarian dynamics and fertility of dairy heifers

• Published in: Journal of dairy science Vol. 94; no. 10; pp. 4997 - 5004
• Main Authors: Lima, F.S., Ayres, H., Favoreto, M.G., Bisinotto, R.S., Greco, L.F., Ribeiro, E.S., Baruselli, P.S., Risco, C.A., Thatcher, W.W., Santos, J.E.P.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.10.2011; Elsevier
• Subjects: 5-d timed artificial insemination; Animal productions; Animals; artificial insemination; Biological and medical sciences; blood; Cattle; controlled internal drug release devices; corpus luteum; dairy heifer; dairy heifers; Dairying; estrus; Estrus Synchronization - drug effects; Female; Fertility - drug effects; Food industries; Fundamental and applied biological sciences. Psychology; gonadotropin releasing hormone; Gonadotropin-Releasing Hormone - administration & dosage; Gonadotropin-Releasing Hormone - pharmacology; Holstein; Hormones - administration & dosage; Hormones - pharmacology; insemination; Insemination, Artificial - veterinary; Milk and cheese industries. Ice creams; Ovary - drug effects; ovulation; Ovulation - drug effects; Ovulation Induction - veterinary; Pregnancy; proestrus; progesterone; Random Allocation; reproduction; Terrestrial animal productions; Time Factors; Vertebrates; 5-d timed artificial insemination; gonadotropin releasing hormone; dairy heifer; reproduction; Hormone; Bovine; Induction; Ox; Gonadotropin; Ovulation; Vertebrata; Reproduction; Mammalia; Fertility; Dairy industry; Artificial insemination; Heifer; Artiodactyla; Timing; Ungulata
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2011-4240

Two experiments evaluated the effects of the first GnRH injection of the 5-d timed artificial insemination (AI) program on ovarian responses and pregnancy per AI (P/AI), and the effect of timing of the final GnRH to induce ovulation relative to AI on P/AI. In experiment 1, 605 Holstein heifers were synchronized for their second insemination and assigned randomly to receive GnRH on study d 0 (n=298) or to remain as untreated controls (n=307). Ovaries were scanned on study d 0 and 5. All heifers received a controlled internal drug-release (CIDR) insert containing progesterone on d 0, a single injection of PGF2α and removal of the CIDR on d 5, and GnRH concurrent with timed AI on d 8. Blood was analyzed for progesterone at AI. Pregnancy was diagnosed on d 32 and 60 after AI. Ovulation on study d 0 was greater for GnRH than control (35.4 vs. 10.6%). Presence of a new corpus luteum (CL) at PGF2α injection was greater for GnRH than for control (43.1 vs. 20.8%), although the proportion of heifers with a CL at PGF2α did not differ between treatments and averaged 87.1%. Progesterone on the day of AI was greater for GnRH than control (0.50±0.07 vs. 0.28±0.07ng/mL). The proportion of heifers at AI with progesterone <0.5ng/mL was less for GnRH than for control (73.8 vs. 88.2%). The proportion of heifers in estrus at AI did not differ between treatments and averaged 66.8%. Pregnancy per AI was not affected by treatment at d 32 or 60 (GnRH=52.5 and 49.8% vs. control=54.1 and 50.0%), and pregnancy loss averaged 6.0%. Responses to GnRH were not influenced by ovarian status on study d 0. In experiment 2, 1,295 heifers were synchronized for their first insemination and assigned randomly to receive a CIDR on d 0, PGF2α and removal of the CIDR on d 5, and either GnRH 56h after PGF2α and AI 16h later (OVS56, n=644) or GnRH concurrent with AI 72h after PGF2α (COS72; n=651). Estrus at AI was greater for COS72 than for OVS56 (61.4 vs. 47.5). Treatment did not affect P/AI on d 32 in heifers displaying signs of estrus at AI, but COS72 improved P/AI compared with OVS56 (55.0 vs. 47.6%) in those not in estrus at AI. Similarly, P/AI on d 60 did not differ between treatments for heifers displaying estrus, but CO S72 improved P/AI compared with OVS56 (53.0 vs. 44.7%) in those not in estrus at AI. Administration of GnRH on the first day of the 5-d timed AI program resulted in low ovulation rate and no improvement in P/AI when heifers received a single PGF2α injection 5 d later. Moreover, extending the proestrus by delaying the final GnRH from 56 to 72h concurrent with AI benefited fertility of dairy heifers that did not display signs of estrus at insemination following the 5-d timed AI protocol.