Where do mycotoxins come from?

Grading rubric in word document attached.
1. A producer has called to ask you for help with a problem they may be having. Calving has just started and about 10-15% of the calves are stillborn. The cows are fine. The local vet, who is helping to get this stopped, thinks it might be the diet the cows are being fed. The diet contains hay and wheat straw. The hay seems fine but the straw stayed in the windrows for a while prior to baling and probably was baled too wet. If you examine the bales about half of them have dark/black streaks of fungus in the stalk. There are few kernels and those that are present are black. The first thing that came to your mind was mycotoxins. Where do mycotoxins come from? Which ones should he test for and why? What is the physiological impact of the mycotoxins that could cause stillbirths? What should he do now?
The pdf included is an example of the ideal format for assignment.