The new U.S. tax law contains provisions that appear to significantly benefit owners and trainers. Blood Horse Daily has an excellent summary that you can find on pages 3-7 here:
http://cdn.bloodhorse.com/daily-app/...y-20180102.pdf
For recreational horseplayers like me, and probably you, nothing seems to have changed. You still can only offset betting losses against winnings so no tax losses for the casual gambler. Professional players, however, seem to have taken one on the chin. I haven't read the actual text of the new law and I'm not giving legal advice (I'm retired and the law license is inactive) but here's the pertinent excerpt from the summary:
"Under the previous law, individuals who itemized their deductions could deduct gambling losses to the extend of gambling winnings. Professional gamblers also were permitted to claim deductions for business expenses incurred in carrying out wagering instructions beyond the amount of winnings recorded. Under the new legislation, all gambling deductions are limited to the extend of gambling winnings."
I don't think this will be popular in Las Vegas and not just with horseplaying professionals.