diff --git a/server/routes/dogs.js b/server/routes/dogs.js
index 631ecfa..9fc25ad 100644
--- a/server/routes/dogs.js
+++ b/server/routes/dogs.js
@@ -32,6 +32,11 @@ const upload = multer({
   }
 });
 
+// Helper function to convert empty strings to null
+const emptyToNull = (value) => {
+  return (value === '' || value === undefined) ? null : value;
+};
+
 // GET all dogs
 router.get('/', (req, res) => {
   try {
@@ -96,10 +101,21 @@ router.post('/', (req, res) => {
     
     const db = getDatabase();
     
+    // Convert empty strings to null for optional fields
     const result = db.prepare(`
       INSERT INTO dogs (name, registration_number, breed, sex, birth_date, color, microchip, notes, photo_urls)
       VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
-    `).run(name, registration_number, breed, sex, birth_date, color, microchip, notes, '[]');
+    `).run(
+      name, 
+      emptyToNull(registration_number), 
+      breed, 
+      sex, 
+      emptyToNull(birth_date), 
+      emptyToNull(color), 
+      emptyToNull(microchip),  // Convert empty string to NULL
+      emptyToNull(notes), 
+      '[]'
+    );
     
     const dogId = result.lastInsertRowid;
     
@@ -127,12 +143,23 @@ router.put('/:id', (req, res) => {
     
     const db = getDatabase();
     
+    // Convert empty strings to null for optional fields
     db.prepare(`
       UPDATE dogs 
       SET name = ?, registration_number = ?, breed = ?, sex = ?, 
           birth_date = ?, color = ?, microchip = ?, notes = ?
       WHERE id = ?
-    `).run(name, registration_number, breed, sex, birth_date, color, microchip, notes, req.params.id);
+    `).run(
+      name, 
+      emptyToNull(registration_number), 
+      breed, 
+      sex, 
+      emptyToNull(birth_date), 
+      emptyToNull(color), 
+      emptyToNull(microchip),  // Convert empty string to NULL
+      emptyToNull(notes), 
+      req.params.id
+    );
     
     // Update parent relationships
     db.prepare('DELETE FROM parents WHERE dog_id = ?').run(req.params.id);