Pregnancy outcomes after change in dose delivery of prostaglandin F2α and time of gonadotropin-releasing hormone injection in a 5-day timed artificial insemination program in lactating dairy cows1

• Published in: Journal of dairy science 2014-12, Vol.97 (12), p.7586-7594
• Main Authors: Stevenson, J.S., Pulley, S.L., Hill, S.L.
• Format: Article
• Language: English
• Subjects: luteal tissue; luteolysis; ovulation; progesterone
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2014-8312

We demonstrated that 50mg of PGF2α on d 6 successfully induced luteolysis in lactating dairy cows enrolled in a traditional 5-d Ovsynch-72 program [GnRH injection 5 d before (d 0; GnRH-1) and 56 (p.m. on d 7; GnRH-2) or 72h (d 8; GnRH-2) after a 25-mg injection of PGF2α (d 5 and 6 after GnRH injection); timed artificial insemination (AI) on d 8]. Our current objective was to determine pregnancy outcomes in lactating dairy cows after a 50-mg injection of PGF2α on d 6 or a 25-mg injection of PGF2α on d 5 and 6 in a 5-d Ovsynch program. Cows in herd 1 diagnosed not pregnant between 30 and 36 d since last AI were enrolled to receive either a 50-mg injection of PGF2α on d 6 (1×50; n=134) or a 25-mg injection of PGF2α on d 5 and 6 (2×25; n=139) after GnRH-1 (d 0), with GnRH-2 at 72h after PGF2α injection (d 5), concurrent with timed AI (d 8). Cows in herd 2 diagnosed not pregnant between 34 and 40 d were treated similarly: even-tagged cows received the 2×25 (n=422) treatment, and odd-tagged cows received the 1×50 (n=450) treatment, except that GnRH-2 was administered at 56h. Blood collected from cows in herd 1 at d 0, 5, 6, and 8 was assayed for progesterone. Luteolysis was defined to occur when progesterone concentration was ≥1ng/mL on d 5, and 72h later (d 8) was either