P4 (e.g. in CIDR) was not allowed for lactating cows so it is not consumed by those drinking the milk. There have been efforts to get it approved in lactating dairy cows with the argument that milk from lactating pregnant cows contain similar level of P4. I have never seen anyone discuss the longer half-life of synthetic P4 and I assume it is what you find in CIDR and other products. Anyone up to date on this issue have comments or suggested reading? Thanks
Yes, CIDR with progesterone is allowed (not "synthetic" progesterone). Dairy cows have progesterone in milk even if not treated and pregnant cows secrete progesterone continuously. Synthetic progestagens such as melengestrol acetate (MGA) are not allowed in milking cows. Progesterone is measured routinely in milk of lactating cows in herds, so it is already present naturally. Natural progesterone is not active orally, otherwise oral contraceptives would us it rather than a synthetic agonist. CIDR has the same progesterone as secreted by the corpus luteum of the cow -- it is not chemically different.
Do you have any information regarding progesterone half life in cattle or other species?
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