Question: I have a stallion in his 30s that I would like to try to get one more foal from but his libido is low with reduced testicle size. I just put him back on TSF-100. Do you have any other suggestions? 
Dr. Kellon: It's entirely possible your stallion's fertility problems are age related.  However, there are several nutrients which influence male fertility including protein, zinc, vitamin C, selenium, vitamin E, vitamin A.  The best thing you can do to support fertility is to feed a high quality and well balanced (minerals) diet.  This should ideally be based on analysis of the diet to determine where deficiencies and imbalances lie but if that is not possible go with a high potency supplement such as U Balance Foundation with addition of liquid E-50 if he is not getting pasture.