Efecto de la GnRH postinseminación sobre la concentración plasmática de progesterona y las tasas de concepción en vacas Holstein repetidoras

Abstract

The purpose of this research was to evaluate the response to the administration of gonadorelin (GnRH) on days 5 and 11 postartificial insemination (PAI) on plasma progesterone concentrations and conception rates in repeat-breeding Holstein cows, under heat stress conditions. Three treatment groups were set at random: T1) 100 I¼,,g gonadorelin on d 5 PAI (GnRH-5, n=33), T2) 100 I¼,,g gonadorelin on d 11 (GnRH-11, n=34) PAI, T3) controls (no GnRH, n=34). Blood samples were collected on d 8, 11, 14, 17, 20, and 23 PAI for the determination of plasma progesterone (P4) concentrations by radio-immuno-assay (RIA). Pregnancy was diagnosed by rectal palpation on d 43 +- 3 PAI. P4 concentrations were higher (P 0.05): T1 (GnRH-5) = 4/33, 12.1 %, T2 (GnRH-11) = 4/34, 11.8 %), T3 (Control) = 5/34, 14.7 %). Cows were inseminated under a temperature/humidity index (THI) ≥,, 72 units, i.e.: heat stress. It was concluded that the administration of GnRH on d 5 resulted in increased plasma progesterone concentrations, but this did not improve conception rates in repeat-breeding Holstein cows under heat stress conditions.