Blood metabolites and hormone-based programmed breeding treatments in anovular lactating dairy cows.

The objectives were to (1) compare blood metabolites and reproductive outcomes in lactating dairy cows not inseminated before (early) and after (late) 100 d in milk (DIM) because of prolonged anovulation or anestrus; and (2) evaluate reproductive responses of cows ≤100 DIM to GnRH+PGF(2α) treatments after a fixed-time artificial insemination (AI; Ovsynch) or after induced estrus (Select Synch). In blood samples collected before initiating hormone-based breeding programs, anovular cows ≤ 100 DIM had the greatest serum total protein and globulin concentrations and the lowest tri-iodothyronine concentrations. Anovular and ovular cows >100 DIM had the greatest serum urea concentrations. Ovaries in cows (n=40) >100 DIM were examined by transrectal ultrasonography, and those without a detectable corpus luteum (CL; anovular) were given GnRH and then PGF(2α) 7 d later (Select Synch), whereas cows with a CL (ovular) were given 2 PGF(2α) injections 12 d apart. Cows were inseminated at observed estrus after the second or only PGF(2α) injection. More ovular (79%; 15/19) than anovular cows (24%; 5/21) were detected in estrus. No differences were detected between ovular and anovular cows in DIM at first AI, conception rate to first AI, cumulative pregnancy rates, number of services per conception, or days open. Cows (n=93) ≤100 DIM were assigned randomly to 3 treatments: (1) control (n=20) AI at estrus; (2) GnRH and then PGF(2α) on 7d (Select Synch; n=42) and monitored for signs of estrus for 5d and AI accordingly; or (3) 2 GnRH injections 9 d apart with PGF(2α) given 48 h before second GnRH injection and AI at 16h after the second GnRH injection (Ovsynch; n=31). Among cows ≤100 DIM, controls had more days to first service (149±16 d) than Select Synch cows (117±7 d). Ovsynch cows had the fewest days to first service (84±10 d) compared with control (149±16 d) and Select Synch (117±7 d) cows. Conception rates in control (25%) and Select Synch (26.2%) cows did not differ from those in Ovsynch cows (29%). Ovsynch cows had greater cumulative pregnancy rates and fewer days open than control (161±20 vs. 258±29 d), but did not differ from Select Synch (233±19d). Timed AI produced comparable fertility and superior cumulative pregnancy rates, fewer days to first service, and fewer days open than AI at observed estrus in cows inseminated ≤100 DIM.
(Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)