The casino opened at Aqueduct in the borough of Queens in October, markedly increasing prize money in the horse races, and 30 horses have since died racing at the track, compared with 15 during the same period a year before, The New York Times reported.
Many of the horses that died since the casino opened had been repeatedly injected with pain mediation in the weeks before their fatal breakdowns, a Times review of veterinary records found.
The newspaper said the widespread use of the drugs indicates how the infusion of cash from the casino has led to incentives to race sore, tired or otherwise unfit horses in hopes of winning a big prize.
New York Gov. Andrew M. Cuomo has ordered an investigation to "ensure against needless injuries to horses and to riders" and experts will look at drugs along with other issues, including track conditions and pre-race inspections.
The Times said more track owners have taken up the gambling industry's offers to increase racing purses through slot machine revenue.
Some experts say purses should be limited so potential winnings in a race don't rise above the value of the horses running.
Casino money at Aqueduct also has increased horse trading, the Times said. Nearly 500 horses and $10.7 million have changed hands since the casino opened, more than double the previous year, records indicated.
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