Your dog's digestion rate isn't affected by his size as much as by other factors, including the type of food you give him, the amount of exercise he gets, the amount of water he drinks and more. For example, an average dog -- big or small -- takes between four and six hours to digest canned wet food.
Every woman's metabolism is different, but as a general rule of thumb, you should allow 1 day for every 1,000 units of hCG you injected. The standard hCG dose is 10,000 units; thus, 10 days after the shot, the synthetic hCG should be gone and you should be able to test for pregnancy without detecting the shot. However, you should ask your doctor what the recommended protocol for your dosage is..
So, how long? Trace amounts of hCG can remain the body for as many as fourteen days after hCG injections. The rule of thumb that doctors use is that it takes one day for each 1000 units of hCG to leave your boy. So, if you get a 10,000 unit injection of hCG, it will take approximately ten days for it to all leave your system. Most doctors will err on the longer side of the time frame to ensure that you get an accurate result.