Output Taxonomy Slugs

Hi, I am using this custom search form that has three different dropdowns that contains a list different taxonomies.

<form role="search" method="get" id="searchform" action="<?php echo bloginfo( 'url' ); ?>">
<input type="hidden" name="" value="" id="" />

<?php echo my_dropdown('genre', 'genre'); ?>
<?php echo my_dropdown('type', 'type'); ?>
<?php echo my_dropdown('ayear', 'ayear'); ?>

<input type="submit" id="searchsubmit" value="Submit" />
</form>

When submitting the form, it’s returning the ID’s rather than the slugs. This is my function,

<?php

function my_dropdown($name, $taxonomy = 'category') {
$defaults = array(
    'taxonomy' => $taxonomy,
    'id'       => $name,
    'name'     => $name,
    'show_option_none' => ' - Select - ',
    'selected' => get_query_var($name)
);

wp_dropdown_categories($defaults);
 } 

add_action('pre_get_posts', 'my_customsearch');
function my_customsearch($query) {   

    if(! $query->is_main_query() || ! $query->is_search )
       return;

    $tax_query = array();
    $genre = (int) get_query_var('genre');
    $type = (int) get_query_var('type');
    $ayear = (int) get_query_var('ayear');

    // first dropdown
    if (! empty($genre) && $genre > 0) {
       $tax_query[] = array(
         'taxonomy' => 'genre',
         'field'    => 'slug',
         'terms'    => $genre
       );
    }

    // second dropdown
    if (! empty($type) && $type > 0) {
       $tax_query[] = array(
         'taxonomy' => 'type',
         'field'    => 'slug',
         'terms'    => $type
       );
    }

    // third dropdown
    if (! empty($ayear) && $ayear > 0) {
       $tax_query[] = array(
         'taxonomy' => 'ayear',
         'field'    => 'slug',
         'terms'    => $ayear
       );
    }

   if ( sizeof($tax_query) > 0 ) {
      $tax_query['relation'] = 'AND';
      $query->set( 'tax_query', $tax_query );
   }

}

// add my custom query vars
add_filter('query_vars', 'mycustom_query_vars'); 

function mycustom_query_vars($query_vars) {
  $query_vars[] = 'genre';
  $query_vars[] = 'type';
  $query_vars[] = 'ayear';

  return $query_vars;
 }

?>