Евгений

function remove_image_size_attributes($html)
{
    return preg_replace('/(width|height)="\d*"/', '', $html);
}

add_filter('post_thumbnail_html', 'remove_image_size_attributes');

<?php
$str = explode(' ', $p['post_title']);
?>
<p id="day"><?php echo  $str[0]; ?></p>
<p id="mounts"><?php echo  $str[1]; ?></p>