The information I have found about this company dose not list the source of its manure, however, since the most common source is a Confined Animal Feeding Operation, CAFO, and since those places do feed the animals a lot of antibiotics, both to attempt to prevent disease but also because it helps the animal put on weight, the manure they sell may well be full of antibiotics.
Antibodies are what the body produces to aid in fighting off diseases so they probably will be in any animal manure as ours.

Whether antibiotic residues in manure will have any detrimental effect on your garden is the question. My gut feeling is that an occasional application will have virtually no effect. Since you probably don't want to add manure continually to the garden anyway, this shouldn't be a problem. Alternate with other composts, especially homemade if you can.

Perhaps this article will be of some use.

Here is a link that might be useful: antibiotics in animal manure