الفهرس 
Introduction
Animals and managementOnly 14 pages are availabe for public view
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Abstract
A total of 35 lactating Friesian cows at 7 day-postpartum, ranging from 4-7 years of age, at 2nd and 4th parity and weighing 450 to 550 kg LBW were used in the 1st experiment to study the effect of GnRH at 14 (G2), 21 (G3) and 28 (G4) day-postpartum or the same treatment beside another GnRH injection at the day of insemination (G2, G3 and G4, respectively) in the 2nd experiment as compared to cows without injection (Control, G1). Cows in all groups were observed for heat signs and pregnancy was confirmed by rectal palpation on d 60 post first artificial insemination. During postpartum period, reproductive efficiency parameters including postpartum first oestrus/service interval (PPFO/SI), interval from treatment to first oestrus/service (PPTO/SI), service period length (SPL), number of services per conception (NSC), days open (DO) and conception rate (CR) were recorded. Milk yield was weekly recorded for 12 wk-postpartum and blood was weekly collected for 7 wk-postpartum.
Results of the 1st experiment conclude that GnRH during different postpartum periods especially on 14 day-PP may help in acceleration of lactating cows to resume their ovarian activity and increasing conception rate during 120 day-PP without pronounced effects on milk yield and haematological parameters. Based on the results of the 2nd experiment, GnRH-injection (2.5 ml Receptal) on 14 day-PP was necessary to accelerate the resumption ovarian postpartum activity in addition to another injection on day of oestrus and insemination to support conception and pregnancy and in turn increasing fertility of dairy cows with low reproductive performance.