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Suppression of ovarian progesterone production in dairy cows using an implant of GnRH‐agonist (deslorelin) for the purpose of evaluating progesterone metabolism
Author(s) -
RABIEE AR,
MACMILLAN KL,
SCHWARZENBERGER F,
THALLER D,
RATHBONE MJ,
TRIGG TE
Publication year - 2001
Publication title -
australian veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.382
H-Index - 59
eISSN - 1751-0813
pISSN - 0005-0423
DOI - 10.1111/j.1751-0813.2001.tb10673.x
Subject(s) - agonist , medicine , endocrinology , implant , chemistry , prostaglandin , zoology , biology , receptor , surgery
Objective To evaluate the potential of an implant of a GnRH‐agonist (deslorelin) to create a progesterone free animal suitable for studying progesterone (P4) metabolism in intact cows by measuring blood P4 and faecal P4 metabolites. Methods Experiment 1: Eighteen non‐lactating cycling Holstein‐Friesian cows, 4 to 7 years old, were allocated to one of three groups to study plasma P4 concentrations preceding an intravaginal insert. These groups comprised: i) a deslorelin group (GnRH‐agonist implanted); ii) a PGF group receiving two injections of prostaglandin (PGF 2a ) 12 days apart; and, iii) an ovariectomised (OVX) group. An intravaginal device (CIDR) was inserted into the vagina of each animal and left in place for 11 days. Plasma P4 concentrations were measured during the study period. Experiment 2: Twelve non‐lactating cycling Holstein‐Friesian cows, 4 to7 years old, were allocated to two groups: i) a deslorelin group (GnRH‐agonist implanted); and ii) an ovariectomised group. Plasma P4 and faecal P4 metabolites (20‐oxo‐pregnanes, 20a‐OH and 20b‐OH) were monitored for a period of 5 weeks. Results Experiment 1: Average plasma P4 concentration did not differ between the three groups (1.28, 1.43 and 1.55 ng/mL for deslorelin, OVX and PGF cows, respectively, P = 0.8) during the period of supplementation. Experiment 2: There was no difference in plasma P4 (mean plasma P4 < 0.02 ng/mL, P = 0.9) and faecal P4 metabolites between deslorelin and OVX cows 2 weeks after the implantation (P = 0.7). Conclusions These data showed that a GnRH‐agonist (deslorelin) implant may be used as an alternative to ovariectomy to create a progesterone free animal suitable for studying the metabolism of administered P4.