Let's take an assumption, each horse runs at uniform speed every time. They all have different but fixed speed tag.
Step 1) Divide the 25 horses into 5 groups. Each group will have 5 horses each.
Step 2) Conduct 5 races for the 5 groups.
Step 3) Conduct an another race with each group winners. (i.e. Fastest from Group 1, Fastest from Group 2, ... , and Fastest from Group 5)
Step 4) Choose the winner from the Step 3. That will be fastest horse. (So, it needs only 6 races to find out the fastest horse of all the 25 horses)
Additionally,
Step 5) Name the horses as below:
{a1,a2,..., a5}--> For the group which has the fastest horse after Step 3 (6th Race)
{b1,b2,...,b5}---> For the group which has the 2nd fastest horse after Step 3
{c1,c2,...,c5}----> For the group which has the 3rd fastest horse after Step 3
{d1,d2,...,d5}---> For the group which has the 4th fastest horse after Step 3
{e1,e2,...,e5}---> For the group which has the 5th fastest horse after Step 3
Where according to their speed, a1>a2>..>a5; b1>b2>..>b5; c1>c2>..>c5; d1>d2>..>d5 and e1>e2>..>e5, also, a1>b1>c1>d1>e1, but not necessarily, b1>a2, c1>b2 etc. [Clearly a1 is the fastest horse]
Step 6) Conduct a race with a2, a3, b1, b2 and c1 to find out the 2nd fastest and 3rd fastest of all the 25 horses.
So, we need to conduct only 7 races to find out the top 3 fastest horses!
A minimum of three.
3 years old (on howrse)
Now
At the time of answering this the Wandering horses are no longer available. So you currently cannot get them.
Nowadays the use of horses has been cut to a minimum. All patrolling is done in cars, and traditional use of horses for crowd control has been stopped.
The minimum period is three months used by most horse owners.
You cannot - the minimum you can trade horses for is 500e.
Trees and branches.
Breeding horses is a complicated process, but luckily there are many resources available online. Numerous low cost books are available through amazon.com as well as many free articles via wikipedia.org.
encryption only windows with built in encryption software is win 7 ultimate
Horses are not a mob yet in Minecraft, but they are available on Mo' Creatures.
The three horses on page 22-23 of I Spy Ultimate Challenger are located on the right side of the page near the bottom, in the middle of the page near the middle, and on the left side of the page near the top.