Cows that do not return to oestrus within 24 days of insemination but are retrospectively diagnosed as not pregnant (non-return, non-pregnant or "Phantom" cows), frequently have a functional corpus luteum (CL) that does not regress. In this study, luteal function around the time of pregnancy diagnosis was compared between pregnant cows and "Phantom" cows with a CL. Cows in two dairy herds that had not returned to oestrus following first insemination were pregnancy tested by ultrasound 5 weeks after insemination. Final analyses included 17 pregnant cows that were cycling normally before being inseminated (CYCP); 22 pregnant cows that had been treated for anoestrus (ANP); and 11 "Phantom" (PC) cows that had not cycled since first insemination and were not pregnant. Blood and CL samples that were collected from each cow between 34 and 38 days after first insemination were assayed for progesterone (P4). Luteal P4 concentrations were similar in pregnant and PC cows (101.6 ± 9.9, 100.7 ± 8.9 and 98.9 ± 12.4 ng/mg for CYCP, ANP and PC cows). Plasma P4 concentrations were also similar (8.5 ± 0.5, 7.6 ± 0.4 and 7.1 ± 0.6 ng/mL) for CYCP, ANP and PC cows. The absence of a return to oestrus in this group of PC cows was most likely related to pregnancy recognition being followed by embryo death and then associated with a failure of luteolysis.

JM, Bowyer-Smyth, J Malmo, and KL Macmillan

Proceedings of the New Zealand Society of Animal Production, Volume 68, Brisbane, Australia, 73-76, 2008
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