How to make a racehorse fast? (a new punchline...)

 The old punchline is "don't feed him."  The new punchline is "CRISPR."

Here's a news story from Nature:

First CRISPR horses spark controversy: what’s next for gene-edited animals?  Horses with genomic edits to make them run faster have been banned from polo, but a zoo of CRISPR-edited animals is gaining acceptance in agriculture.  By Katie Kavanagh 

"The horses are clones of the prize-winning steed Polo Pureza, but they have a tweak to myostatin — a gene involved in regulating muscle development — that is designed to quicken their pace. CRISPR was used in fetal fibroblasts (connective tissue cells) to generate embryos through cloning, and then the embryos were implanted into mares.

"The development of these five CRISPR-edited horses ten months ago, by the non-profit research organization Kheiron Biotech in Buenos Aires, is proving controversial among horse breeders in Argentina, where polo is extremely popular, Reuters reported on 30 August.

"Critics are concerned that the technology threatens people’s livelihoods and that it will compromise the tradition of using selective breeding to generate elite horses. The Argentine Polo Association has now banned the use of gene-edited horses in the sport, following the lead of similar organizations such as the International Federation for Equestrian Sports1, which banned the practice in 2019."