Tasas de concepción en respuesta a dosis reducidas de somatotropina en vacas holstein, durante la sincronización del estro

Abstract

The objective of this research was to determine the effect on the conception rates of Holstein cows, when served 2 reduced doses of recombinant bovine somatropin (STbr) (250 mgs, each, sc) in day 56 postpartum, and at the artificial insemination time. The experiment took place in a stable of the Comarca Lagunera, Mexico, from August 2004 to April 2005. A group of multíparous cows (n=264) of first service were used with a number 3 corporal condition. All of them were put under a prostaglandin F2á (days 28 and 42 PP) and GnRH (day 56 PP) estro synchronization protocol. They were divided in two groups; Witness Group (GTES, n=156) with cows to which a placebo was administered; and STbr Group (GSTbr, n=108), with cows to which one first dose of 250 mgs of STbr in postpartal day 56 was injected. The second 250 mgs to STbr dose was applied at the artificial insemination time (67 ± 2 days postpartum). Blood samples in 10 cows of each group, were taken every two days, during 12 days. The concentrations of IGF-I by means of a inmunoradiométrico test were determined. The gestation diagnosis was performed by rectal palpation at 45 ± 3 days post-insemination. The conception rates between groups were compared by means of logistic concentration and regression analysis of IGF-I. A com pletely randomized experimental design with repeated measurements was applied. The conception rates in the group of cows under STbr treatment (65,77 ± 4,57%) were higher (P<0.05) that those in the witness group (56,49 ± 3,97%). The IGF-I concentrations were higher (P<0.05) in GSTbr than in GTES in 58 and 66 days postpartum. The results of this study allow to conclude that with the administration of 2 reduced doses of STbr, in postpartal day 56, and at the time of the artificial insemination, the rates of conception of Holstein cows of first service were increased.