Efecto del norgestomet inyectado sobre el folículo dominante persistente y a formación del cuerpo lúteo en vacas sincronizadas con implantes de norgestomet

Abstract

THE EFFECT OF A 3 MG IMINJECTION OF NORGESTOMET (NG) ON ATRESIA OF PERSISTENT DOMINANT FOLLICLES (PDF), AND CORPORA LUTEA (CL) FORMATION AFTER INDUCED OVULATION WITH HCG IN PROGESTAGEN ESTRUS SYNCHRONIZED BOVINE FEMALES WAS STUDIED IN 11 HOLSTEIN HEIFERS AND 20 LACTATING COWS. ESTRUS OF ALL ANIMALS WAS SYNCHRONIZED WITH A DOUBLE PGF2A INJECTION. ON DAY 7 AFTER ESTRUS (DAY 0 OF THE EXPERIMENT) ALL ANIMALS RECEIVED A 3 MGNG SC EAR IMPLANT (ING), AND A LUTEOLYTIC DOSE OF PGF2A. THENGIMPLANT WAS REMOVED ON DAY 9. COWS AND HEIFERS WERE RANDOMLY DISTRIBUTED TO EACH OF THE FOUR TREATMENTS: HCG (N = 8) WITH 2500 I.U. OF HCG IM ON DAY 3; HCG NG (N = 8) WITH 2 500 I.U. HCG IM ON DAY 3, AND 3MG NG IMON DAY 5; NG(N = 8) WITH 3MG NG IMON DAY 5; AND THE CONTROL (C, N = 7), SALINE SOLUTION IM ON DAY 3 AND 5ML VEGETABLE OIL ON DAY 5. DAILY ULTRASOUND (US) IMAGES OF THE OVARIES, AND BLOOD SAMPLES WERE TAKEN FROM IMPLANTATION UNTIL THE END OF THE SYNCHRONIZED ESTRUS. PROGESTERONE CONCENTRATIONS WERE DETERMINED IN PLASMA BY RIA. ATRESIA AND SUBSTITUTION OF THE PDF WAS SIMILAR (P > 0.05) BETWEEN HCG (5/8), HCG NG (7/8) AND NG (6/7), BUT DIFFERENT TO C (0/7, P < 0.05). PREGNANCY RATES IN THE SYNCHRONIZED ESTRUS WERE NOT DIFFERENT (0.05<0.1) BETWEEN COWS THAT OVULATED THE PDF (53%, 7/13), OR A NEW FOLLICLE (66.6%, 12/18). IN HCG NG, CL FORMATION WAS AVOIDED; ONLY 1/6 ANIMALS SHOWED PROGESTERONE LEVELS >1 NG/ML AT IMPLANT REMOVAL, WHILE INHCGGROUP 5/5 OVULATED ANIMALS FORMED A CL, HAD PROGESTERONE LEVELS >1.0 NG/ML, AND WERE NOT ESTRUS SYNCHRONIZED AT IMPLANT REMOVAL. THE INJECTION OF 3 MG IM OF NG ON DAY 5 AFTER ING INSERTION CAUSED ATRESIA AND SUBSTITUTION OF THE PDF, AND AVOIDED CL FORMATION IN HCG INDUCED OVULATORS.