We have had incidents of cows aborting their calves three months early, and premature births. This is the first year we have ever had a problem of this nature. We are in an isolated area with no neighboring cattle. The only thing we have done differently this year is we are feeding bought rye grass hay along with our own meadow hay, and we used Ivomec Plus in mid January. We start calving the first of March. Our local vet said they have seen a higher incident of this problem this year in our area. Autopsies do not show anything unusual.Any thoughts as to what may be causing this?