29 September 1995

signals…

Pregnant

HIGH rates of embryo loss are linked to cows which show a delayed rise in progesterone after mating.

Dr George Mann of Nottingham Universitys Cattle Fertility Group said that when a cow is mated successfully, progesterone is responsible for controlling the growth of the early embryo.

Progesterone is produced by the corpus luteum (CL) on the ovary in the luteal phase (see box). At the end of the phase the cow triggers the CL to regress and progesterone production to fall in a process called luteolysis. To survive the embryo must prevent luteolysis and maintain the CL. It does so by sending a signal (known as interferon) to its mother.

This critical "maternal recognition of pregnancy" stage is day 13 to 21 post mating.

Dr Manns research has shown that a delayed rise in progesterone after mating increases the mothers drive to start cycling again, and weaken the embryos signal to its mother.

"Such anomalies have devasting effects on conception rate," he said. "If the embryos signal to its mother fails, the cow fails to recognise that she is pregnant, progesterone level drops and the embryo is lost."

Cows with an extended inter-luteal phase – days between progesterone fall and the progesterone rise in the next cycle – had a reduced luteal phase. For each day the luteal interval increased above eight, luteal phase fell by 0.9 days and risk pregnancy failure due to earlier embryo loss increased.

Prof Lamming said cows identified by milk progesterone profiling as having no progesterone rise by day five after mating should be considered for vet treatment.

involving progesterone supplementation.

Dr George Mann: "If the embryos signal to its mother fails, the cow wont recognise that she is pregnant."