Evaluation of reproductive performance in lactating dairy cows with prostaglandin F-2 alpha gonadotropin-releasing hormone, and timed artificial insemination

Nine hundred and twenty Holstein cows from 16 commercial dairy herds to eva luate three systematic breeding protocols: 14-d PGF(2 alpha), timed artific ial insemination (AI), and GnRH-PGF(2 alpha), relative to AI following estr us detection without hormone intervention. The timed AI protocol involved G nRH, followed by PGF(2 alpha) 7 d later and GnRH again 2 d after PGF(2 alph a), with AI 6 to 18 h after the second GnRH. The GnRH-PGF(2 alpha) protocol consisted of GnRH followed by PGF(2 alpha) 7 d later. Eight herds relied o n visual observation to detect estrus, and eight herds utilized the HeatWat ch estrus detection system. The average interval to first postpartum AI was shortest for the timed AI protocol (77.1 d) followed by the 14-d PGF(2 alp ha) protocol (81.6 d). There was no difference in days to first AI between the control (86.1 d) and GnRH-PGF(2 alpha) (89.5 d) protocols. Percent preg nant per first AI did not differ among control (45.6%), 14-d PGF(2 alpha) ( 43.7%), or GnRH-PGF(2 alpha) (44.0%) protocols, but all protocols had a hig her percent pregnant per first AI than the timed AI protocol (30.1%). Respo nse to the GnRH-PGF(2 alpha) protocol was limited because 44.0% of the cows submitted to the protocol were not detected in estrus <10 d post-PGF(2 alp ha) administration and had an interval to first AI of 103.8 d. Cumulative p ercent pregnant by 120 d postpartum did not differ between control cows (53 .1%) and hormonally treated cows (50.6%). Visual observation herds had a sh orter interval to first postpartum AI (82.8 d) than the HeatWatch herds (84 .8 d), with a higher overall rate of estrus detection across all protocols (75.3 and 67.6%, respectively).