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Altered ovarian dynamics in lactating dairy cows undergoing embryonic mortality
Our objective was to characterize ovarian dynamics in lactating dairy cows undergoing embryonic mortality. Cows (n=62) received timed AI at 60 to 79 DIM after Presynch-Ovsynch. At AI, cows were blocked by parity (primiparous vs. multiparous) and randomly assigned to AI with regular semen (n=52) or extender only (n=10; Cycling; CY). Blood was collected every 48 h from 14 to 42 d after AI to determine concentrations of progesterone (P4) and pregnancy specific protein B (PSPB). Transrectal ultrasound was performed daily to assess ovarian dynamics. Cows were considered: 1) pregnant (PG; n=18) if a viable embryo with a heartbeat was observed, 2) embryonic mortality (EM; n=6) when a viable embryo or its heartbeat was no longer observed, and/or PSPB concentrations were initially above and then below 0.8 ng/mL, and 3) Non-pregnant (NP; n=28) when no viable embryo was observed and PSPB concentrations remained below 0.8 ng/mL. Pregnant and EM cows had greater (P<0.01) PSPB concentrations than NP and CY cows beginning 24 d after AI. Percentage of cows with complete luteal regression (CLR) was affected (P=0.02) by group (CY and NP=100 vs 66.7% for EM) and occurred later (P<0.01) in EM (39.5±2.1) than in CY and NP cows (20.2±1.3 and 22.9±0.8). At 18 d after AI, NP cows had greater (P<0.05) P4 than CY cows whereas EM and PG cows had greater (P<0.05) P4 concentrations than CY and NP cows. Among cows with CLR, the percentage ovulating was similar (P=0.21) for CY, NP, and EM (90.0, 85.7, and 50.0%) cows. The interovulatory interval (IOI) was affected by group (P<0.01). Cycling cows had the fewest days to ovulation (22.9±0.96) followed by NP cows (25.8±0.6) whereas EM cows had the longest interval to ovulation (40.0±2.0 d). Days from CLR to ovulation was similar (P=0.52) for CY (5.0±0.9), NP (6.0±0.6), and EM (7.0±1.9) cows. Ovulatory follicle growth rate for the 5 d preceding ovulation was similar (P=0.28) for all groups (CY=1.6±0.2, NP=1.5±0.1 and EM=0.8±0.5 mm/day). Likewise, diameter at ovulation was similar (P=0.77) for all groups (CY=22.7±1.1, NP=23.9±1.8 and EM=24.8±3.8 mm). Thus, cows with EM were less likely to undergo complete luteal regression, and had extended IOI. The observed differences in IOI were due to delayed luteal regression rather than alterations in follicular wave dynamics. The longer IOI for NP than CY cows may have been caused by undetected EM. Supported by Hatch project NYC127813
Keywords:
Ovarian dynamics
Embryonic mortality
Dairy cow