Exiting Victoria Park along with Horwood are Nathan Buddle, Paul Johnson, Nathan Luscombe, Adam McHugh and Colin Nish.
But the club, relegated from npower League One this season, have exercised the option on the contracts to keep Neil Austin, Lewis Hawkins and James Poole.
A statement on Hartlepool’s official website said: “The chairman and everyone at the club would like to thank all of the players for their services and commitment to the club and wish them all the very best for the future.
“Discussions are continuing with other remaining first-team players and more information will be made available in due course.”
Mattia De Sciglio stunned that Juventus were shocked to be held to a goalless draw with SPAL on Saturday.
Sunderland have suspended midfielder Darron Gibson with immediate effect after he was charged with drink driving.
Jose Mourinho's recent bad frame of mind was still present despite Manchester United beating Brighton 2-0 at Old Trafford on Saturday, a result that puts them into the last four of the FA Cup.
Mohamed Salah continued his astounding goalscoring form on Saturday, hitting four goals as Liverpool thrashed Watford 5-0 at Anfield.