Have you ever had cattle consume fertilizer?  It can happen, and depending on the product, can be a significant problem.  If it contains nitrate (ammonium nitrate or potassium nitrate), it can lead to nitrate poisoning.  Nitrate itself is not poisonous, but it is converted to nitrite in the digestive system.  According to Charlie Stoltenow, North Dakota State University Extension Service veterinarian, nitrite is 10x more toxic than nitrate. 

Nitrite is absorbed into the red blood cells and combines with hemoglobin to form methemoglobin. Methemoglobin cannot transport oxygen as effectively as hemoglobin, so the animal’s heart rate and respiration increase. The blood and tissues of the animal take on a blue to chocolate brown tinge, muscle tremors can develop, staggering occurs and the animal eventually suffocates.

“Fertilizer is good for plants, but not good for cattle,” Stoltenow says. 

I wonder what he thinks about using urea or urea-based feeds as a protein source in finishing cattle?

According to the article, the best way of preventing fertilizer-related nitrate poisoning in cattle is by controlling access to fertilizer. Avoid letting cattle graze immediately after spreading fertilizer and clean up fertilizer spills. Areas where the fertilizer spreader turns or areas where filling (and consequently spilling) take place may have excessive quantities of nitrate available to the cattle. Also, do not allow cattle to have access to areas where fertilizers are stored.

You can read more here:

 www.plantmanagementnetwork.org/pub/fg/news/2009/Fertilizer/

SuperCal 98G & SuperCal SO4 are produced from products that are commonly found in nature (calcium carbonate & calcium sulfate, respectively).  They are not toxic to humans or animals.