<?php
//Values from feed examples: 123, 234, 345
$valuesFromFeed = array(123, 234, 345); //These are not in my code, they are values from the XML feed

while ($uniqueIdentifier = $valueFromFeed) {
    <input type="hidden" name="horse_<?php echo $uniqueIdentifier; ?>" />
}
?>

<?php
if (isset($_POST['horse_' . $uniqueIdetifier])) {
    echo "You got the right thing here.";
} else {
    echo "Still no joy.";
}
?>

<form action="/horses/my_unique_horse_name">
  ...
</form>

<form action="/horses/another_horse_name">
  ...
</form>

<form action="/horses/">
  <input type="hidden" value="my_unique_horse_name'>
</form>

<form action="/horses/">
  <input type="hidden" value="another_horse_name'>
</form>

<form method="/horses/">
  <button type="submit" value="my_unique_horse_name">My Horse</button>
  <button type="submit" value="another_horse_name">Another Horse</button>
</form>