Public companies with ties to Thoroughbred racing slumped from 1-20% Monday as the resignation of Tyco International's chairman and growing investor skepticism dragged down the entire market.The Dow Jones Industrial Average was down 172 points, or 1.8%, and the Nasdaq Composite was off 45 points, or 2.8%, by 3:30 p.m. Both markets haven't been this low in more than a month, according to financial news services.In terms of dollars, Penn National Gaming has taken the biggest hit of the day falling $2.75, or nearly 9%, to $33.34 on moderately heavy trading. By percentage, the penny stock TrackPower dropped one cent per share and lost 20% of its value. MTR Gaming, the owner of Mountaineer Race Track and Gaming Resort in West Virginia, lost nearly 7% ($1.13) of its stock value and Youbet.com lost 6.1% ($0.05).Churchill Downs stock fell 65 cents to $34.35, or 1.86%, and Magna Entertainment dropped 24 cents per share, or 3.10%.The resignation of Tyco International chief executive officer and chairman Dennis Kozlowski apparently aggravated already shaky conditions among investors. Kozlowski resigned for "personal reasons" after it was revealed he is under investigation for evading New York sales taxes. Tyco International is the largest manufacturer of electrical connectors and securities alarm systems.Bloomberg reported that energy companies Williams Cos. and El Paso Corp. plummeted. Their trading business is shrinking amid disclosures of sham transactions by rivals and increased scrutiny by state regulators, all part of the continuing fallout from Enron's spectacular collapse. ''You can't ignore that we have a loss of investor confidence,'' Susan Everly told Bloomberg. Everly manages $5 billion in large-company stocks at Credit Suisse Asset Management.