A synthetic hormone used as a growth promotant in cattle is?

The synthetic hormone used as a growth promotant in cattle is bovine somatotropin (bST), also known as recombinant bovine somatotropin (rBST).

Here's why:

* bST is a synthetic version of the naturally occurring hormone somatotropin, produced by the pituitary gland in cattle.

* rBST is a genetically engineered form of bST produced in the laboratory.

* Growth promotion: When administered to cattle, bST/rBST stimulates milk production, increases muscle growth, and improves feed efficiency.

It's important to note that the use of bST/rBST is controversial, with concerns regarding its potential health impacts on both animals and humans.