https://www.vetsurgeon.org/f/clinical-questions/17664/how-long-after-castration-before-you-can-say-a-cat-is-sterile Got a phone call the other day asking this, never been asked it before. With dogs we always say several weeks (anything between 4 - 6 depending on who answers I think!). I had always been under the impression this was because some sperm may be storeden-USTelligent Community 10https://www.vetsurgeon.org/thread/105836?ContentTypeID=1Sun, 26 Jan 2014 16:03:01 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:4475799c-2603-4e86-8681-254520eaaae7Charlotte Marshall<p>Longer for cats than dogs, that suprises me. I think I told her a month so i&#39;ll have to keep my fingers crossed<img src="https://www.vetsurgeon.org/emoticons/v2/Happy_smiley.png" alt="Happy" /></p><div style="clear:both;"></div>https://www.vetsurgeon.org/thread/105835?ContentTypeID=1Sun, 26 Jan 2014 15:53:06 GMT146601cc-3922-4be7-9974-7e1d4e45a66b:df016880-e076-40ad-8727-ca1e96485ce2Birte Toft<p>I trawled the internet for this a while back. The most reliable source I found was UC Davis, if I remember correctly, so I&#39;ve stuck with their suggestions of up to 21 days for dogs and 49 for cats. For rabbits we&nbsp;recommend 30 days, rightly or wrongly. I&#39;d love to be able to explain this to clients in a more scientific way than &quot;he might be carrying a round in the chamber, heh heh&quot;, so hopefully someone here has a more useful contribution.</p><div style="clear:both;"></div>