Effects on the oestrous cycle of dairy cows of the administration of colostrum in the mid-luteal phase.

A group of 13 cows were dosed orally nine or 10 days after a normal oestrous cycle; six animals received colostrum, five animals received milk containing varying amounts of oestrone sulphate, and two cows were given milk containing a low level of oestrone sulphate. Measurements of milk progesterone levels after dosing showed that colostrum had an apparent luteolytic effect, milk containing oestrone sulphate at a level of 2000 pg/ml had a less marked effect on milk progesterone and those animals receiving milk showed no reduction in milk progesterone. These results show that there is a physiological basis for the practice of inducing overt oestrus in cows showing no visible oestrus, by dosing them with colostrum.