Evaluation of GnRH treatment 12 days after AI in the reproductive performance of dairy cows

The objective of this study was to evaluate the effects of GnRH administered at Day 12 post-AI on the reproductive performance of dairy cows. Holstein-Friesian dairy cows (n = 103) on a large Hungarian dairy farm were allocated randomly to treated (n = 54) or control (n = 49) groups. Twelve days after AI, treated cows received a GnRH agonist i.m., while the control group received a placebo (physiological saline). Progesterone radioimmunoassay was used to determine the correct timing of artificial insemination (Day 0) and the incidence of luteal insufficiency on Day 12. Ultrasonography and radioimmunoassay for pregnancy-associated glycoprotein were used to detect pregnancy and late embryonic/fetal mortality between Days 32 and 55 after AI. Three cows from each group were inseminated when progesterone concentrations were > 1.0 ng/mL, and six cows (four from the treated and two from the control group) had luteal insufficiency (progesterone < 1.0 ng/mL) on Day 12. Late embryonic/fetal mortality occurred in three treated cows and in two control cows. When these cows were removed from the model, calving rates after first service were 59.6% (28/47) and 59.1% (26/44) for treated and control cows, respectively (P > 0.05). There was no significant difference between treated and control cows when they were inseminated before or after Day 100 from calving. In summary, administration of a GnRH agonist on Day 12 after AI did not improve reproductive performance in dairy cows. However, our approach may be used for the field evaluation of different treatment protocols. (c) 2006 Elsevier Inc. All rights reserved.