Lothian and Borders Police's top police horse 'Trooper' on his last working day as a police horse with his current rider PC Douglas Tait in Inverleith Park in Edinburgh, Tuesday November 1, 2005. Trooper, who is now 21-years-old is the force's longest serving police horse, having joined the Mounted Section approximately 16 years ago. See PA story SCOTLAND Horse. PRESS ASSOCIATION photo. Photo credit should read: Andrew Milligan/PA.