PROGESTERONE supplementation five days after insemination doubled pregnancy rates in dairy cows with low levels of the hormone in their blood.
But parlour in-line progesterone monitoring and more understanding of how diet affects progesterone levels are needed before the technique can be used commercially, according to a study conducted at Nottingham University.
University researcher Gareth Starbuck says: "The greatest cause of insemination failure is early embryo mortality; the loss of viable embryos within 25 days of insemination." (see table).
Progesterone helps early embryo survival by channelling nutrients to the embryo. "For an insemination to be successful, cow progesterone production should start within five days of insemination," he adds.
"Pregnancy rates in cows with a milk progesterone concentration below 3ng/ml are significantly lower than those with levels above 3ng/ml."
Although progesterone supplementation has been attempted in the past, it has usually been given to all animals. In his latest trial, Mr Starbuck was keen to target only animals that needed supplementation – those with milk progesterone levels below 3ng/ml.
An intra-vaginal progesterone releasing device, similar to that used for heat synchronisation was used to supplement deficient cows.
"Pregnancy rate in unsupplemented animals with milk progesterone levels of 1-2ng/ml was low, at 29%. Following supplementation, pregnancy rates in these animals rose to 58%."
In practice, the extra labour involved in testing milk to establish which animals need supplementation may put some producers off. An additional concern is that progesterone releasing devices are not currently licenced for use as supplements.
But when in-line progesterone monitoring in the parlour becomes available in a few years time, increasing progesterone levels in deficient cows could be possible on-farm, says Mr Starbuck.
results for all cows
Fertilisation failure 10%
Early embryo mortality 30%
Late embryo mortality 10%