Re: Bulls testicle size determine fertility

Glen:

There is a direct relationship to testicular size and fertility in heathy 
mammals.  However, there are certain circumstances where testes size may 
not be related to fertility.  For example, in the case of testosterone (T)
deficiency, the testes may actually be larger than normal. This is due to 
the loss of T feedback inhibition of Luteinizing hormone (LH) from the 
anterior lobe of the pituitary gland.  As LH causes the testes to enlarge, 
if the secretion of LH is not kept in check by T feedback inhibition, the 
testes could be stimulated to increase in size. As T is necessary for 
spermatogenesis, the T deficiency would lead to infertility, but the 
testes size would remain large because of LH stimulation.  

Of course, other conditions such as testicular cancers will change the 
size of the glands and can wreak havoc on fertility.

David Mallory
Department of Biological Sciences
Marshall University
Huntington, WV