During the dark hours, melatonin is secreted from the pineal gland, and the length of melatonin secretion is thought to be the trigger or signal for initiation for cycling. A greater environmental influence is length of day, which can be manipulated to provide 16 hours of darkness per day for 40 to 60 days, he said. I recommend starting your flushing period 14 days before you put in your intact rams and continuing 14 days into breeding. If the ewes are thin, I would continue for an additional 14 days or as needed. Replace with intact rams after 14 days.
Timing is important.
The teaser ram should initiate ovulatory activity in three to five days. If you wait 20 days, you could miss the estrus, and it would be another 17 days before they cycle again. Abrupt introduction of rams to isolated ewe will cause a synchronized estrus and group lambing in two waves 17 days apart. The ram effect is only beneficial if true ewe isolation has been achieved. It may cause only a portion of anestrous ewes to start cycling, it may only stimulate one estrous cycle in anestrous ewes, and it won't affect any ewes that are already cycling.