Influence of inducing luteal regression before a modified controlled internal drug-releasing device treatment on control of follicular development

• Published in: Journal of animal science 2011-11, Vol.89 (11), p.3531-3541
• Main Authors: Grant, J. K, Abreu, F. M, Hojer, N. L, Fields, S. D, Perry, B. L, Perry, G. A
• Format: Article
• Language: English
• Subjects: Animal productions; Animals; beef; Biological and medical sciences; Cattle - physiology; controlled internal drug release devices; Dinoprost - administration & dosage; Dinoprost - pharmacology; Estradiol - blood; estrus; Female; follicular development; Fundamental and applied biological sciences. Psychology; gonadotropin-releasing hormone; Gonadotropin-Releasing Hormone - administration & dosage; Gonadotropin-Releasing Hormone - pharmacology; heifers; Logistic Models; luteinizing hormone; Luteinizing Hormone - blood; Luteolysis - drug effects; Luteolysis - physiology; Ovarian Follicle - diagnostic imaging; Ovarian Follicle - drug effects; Ovarian Follicle - physiology; ovulation; Ovulation Induction - methods; Ovulation Induction - veterinary; progesterone; Progesterone - blood; Random Allocation; Terrestrial animal productions; Ultrasonography; variance; Vertebrates
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2011-3852

At the initiation of most controlled internal drug-releasing (CIDR) device protocols, GnRH has been used to induce ovulation and reset follicular waves; however, its ability to initiate a new follicular wave is variable and dependent on stage of the estrous cycle. The objectives of the current studies were to determine 1) if inducing luteal regression before the injection of GnRH at time of insertion of a CIDR resulted in increased control of follicular development, and 2) if removing endogenous progesterone by inducing luteal regression before insertion of the CIDR decreased variation in LH pulse frequency. In Exp. 1 and 2, Angus-cross cycling beef heifers (n = 22 and 38, respectively) were allotted to 1 of 2 treatments: 1) heifers received an injection of PGF2α on d –3, an injection of GnRH and insertion of a CIDR on d 0, and a PGF2α injection and CIDR removal on d 6 (PG-CIDR) or 2) an injection of GnRH and insertion of a CIDR on d 0 and on d 7 an injection of PGF2α and removal of CIDR (Select Synch + CIDR). In Exp. 3, Angus-cross beef heifers (n = 15) were assigned to 1 of 3 treatments: 1) PG-CIDR; 2) PGF2α on d –3, GnRH on d 0, and PGF2α on d 6 (PG-No CIDR); or 3) Select Synch + CIDR. Follicular development and ovulatory response were determined by transrectal ultrasonography. Across all experiments, more (P = 0.02) heifers treated with PG before GnRH initiated a new follicular wave after the injection of GnRH compared with Select Synch + CIDR-treated heifers. In Exp. 1, after CIDR removal, interval to estrus did not differ (P = 0.18) between treatments; however, the variance for the interval to estrus was reduced (P < 0.01) in PG-CIDR heifers compared with Select Synch + CIDR heifers. In Exp. 3, there was a tendency (P = 0.09) for LH pulse frequency to be greater among PG-CIDR and PG-No CIDR compared with the Select Synch + CIDR, but area under the curve, mean LH concentrations, and mean amplitude did not differ (P > 0.76). In summary, induction of luteal regression before an injection of GnRH increased the percentage of heifers initiating a new follicular wave. Removal of endogenous progesterone tended to increase LH pulse frequency, and the modified treatment increased the synchrony of estrus after CIDR removal.