Pregnancy rate in dairy cows treated with human chorionic gonadotropin five days after insemination

Abstract

espanolRESUMEN: Este estudio evaluo si la administracion de hCG cinco dias despues de la inseminacion incrementa la concentracion de progesterona y la tasa de prenez (TP) en vacas lecheras. Se utilizaron 989 vacas Holstein de diferente numero de parto y servicio. Las vacas se inseminaron despues de la deteccion del estro o a tiempo fijo. El dia cinco postinseminacion las vacas se asignaron aleatoriamente a dos tratamientos: hCG (n=482), donde recibieron 3500 UI de hCG via im; y control (n=507), donde no recibieron tratamiento. Se diagnostico la gestacion mediante ecografia el dia 30 posinseminacion y se confirmo el dia 60 por palpacion transrectal. En 15 vacas de cada tratamiento se determino la concentracion plasmatica de progesterona los dias 5, 11 y 15 postinseminacion. Se analizo la TP mediante regresion logistica y la concentracion de progesterona mediante analisis de varianza. La concentracion de progesterona fue mas alta los dias 11 y 15 en las vacas tratadas con hCG que en las control (P0.1). Se concluye que la inyeccion de hCG cinco dias despues de la inseminacion incrementa la concentracion de progesterona y la tasa de prenez en vacas lecheras. EnglishABSTRACT: This study tested whether the administration of hCG five days after insemination increased progesterone concentration and pregnancy rate (PR) in dairy cows. A total of 989 lactating Holstein cows with different parity and number of prior services were used. Cows were inseminated after overt estrus or at a fixed-time. Five days post-insemination, cows were randomly assigned to two treatment groups: hCG (n=482), which received 3500 IU of hCG by intramuscular injection; and the control group (n=507), which did not receive any treatment. Pregnancy was diagnosed by ultrasound on day 30 post-insemination, and gestation was confirmed on day 60 post-insemination by rectal palpation. In 15 cows from each treatment group, plasma progesterone concentration was determined on days 5, 11, and 15 post-insemination. Pregnancy rate was analysed using logistic regression. Variations in progesterone concentration between treatments were tested by ANOVA for repeated measurements. Progesterone concentration was higher on days 11 and 15 in cows treated with hCG, compared to the control group (P0.1). We conclude that injection of hCG five days after insemination increased progesterone concentration and pregnancy rate in dairy cows.