While I know do believe that environmental stress can affect embryos, I can hardly believe that a drop in temperature to 30 degrees can affect them. I flush cows year round and they are all maintained in outside pens at the ET center. I have had some excellent flushes in some pretty wicked winter weather. One of the best flushes I have had was on a day where the wind chill was equivalent to -58 degrees. It was -35 with a stiff breeze and one donor produced 38 grade 1 embryos. We had 3 cows flushed that day and we froze 59 grade 1 embryos.
There are so many factors that affect the embryos and their survival. One Tuesday of this week, we flushed 4 cows at the ET center. From one donor we froze 25 out of 27 embryos produced, from the second we froze 12 out of 19 embryos produced , from the third donor we froze 10 out of 20 embryos produced, and from the fourth, we got 5 dead embryos and 5 unfertilized embryos, from very high quality semen. This happens once in awhile, and we have no idea why this happens.
Listen to what Justintime has to say. I can tell he has been there, down that when it comes o ET. I have found that only hot weather has much of an affect on results. The cooler, the better for AI and ET.
There are great variations in how different cows react to the flush drugs. My donor who produced 25 grade 1 embryos has been flushed 7 times in the past 14 months. She has now produced 407 grade 1 embryos and she shows no signs of ever been flushed. I have other cows that have been flushed twice and I can tell they have been flushed as their tail heads have risen, they are coarser fronted and harder to get rebred.