Effect of an implant containing the GnRH agonist deslorelin on secretion of LH, ovarian activity and milk yield of postpartum dairy cows

Prevention of high plasma progesterone concentrations in the early postpart um period may improve fertility. Our objective was to determine whether a D eslorelin implant (DESL; 2100 mug, SC) would reduce secretion of LH and alt er follicle dynamics, plasma concentrations of progesterone, estradiol and PGF(2 alpha) metabolite (PGFM) in postpartum dairy cows. Cows received DESL on Day 7 postpartum (Day 7, n=8) or were untreated (Control, n=9). All cow s were injected with GnRH (100 mug, im) on Day 14 to assess LH response. A protocol for synchronization of ovulation with timed AT was initiated an Da y 60 (GnRH [Day 60], CIDR [Day 60 to Day 67], PGF(2 alpha) [Day 67, 25 mg a nd Day 68, 15 mg], GnRH [Day 69], AI [Day 70]). The LH response to injectio n of GnRH on Day 14 was blocked in animals treated with DESL. Numbers of Cl ass 1 (<6 mm) follicles were unaffected (P > 0.05) whereas numbers of Class 2 (6 to 9 mm) (P < 0.01) and Class 3 (>9 mm) follicles were less (P < 0.01 ) in DESL cows between Day 7 and Day 21. From Day 22 to Day 60, DESL-treate d cows had more of Class I follicles and less Class 2 (P < 0.01) and Class 3 (P < 0.01) follicles, and Lower plasma concentrations of progesterone and estradiol (P < 0.01). Concentrations of PGFM between Day 7 and Day 42 were not affected by treatment (P > 0.05). All cows ovulated in response to GnR H on Day 69. Subsequent luteal phase increases in plasma progesterone conce ntrations (Day 70 to Day 84) did not differ. The use of the DESL, implant a ssociated with PGF(2 alpha) given 14 days later suppressed ovarian activity and caused plasma progesterone concentrations to remain < 1 ng/mL between Day 22 and Day 51. The DESL implant did not affect milk production. (C) 200 1 by Elsevier Science Inc.