The bottom line is the spit test is not an argument against ultrasonic pregnancy testing with the Preg-Tone. Interpretation of the spit test is more of an art, than an obvious yes or no indicator.
A lot depends on the temperament of the female. In general when the female is pregnant she will spit at a male if he comes near her. But many females will also spit at the male if they do not have a mature follicle on their ovary. The follicular wave is about 14 days. So for a period of about 3-5 days, there is a mature follicle and the female will be the most receptive to breeding.
After the initial breeding, if the spit test is continued every 7-10 days through out the entire 345 days of pregnancy, then you will have a fairly accurate spit test. The reason that ultrasonic testing with the Preg-Tone is a better indicator of a continued pregnancy, is that nobody will spit test every week; it’s way too much work (and the handler often is caught in the “crossfire”–very gross!!). Most will spit test for a couple weeks and maybe continue monthly if they are really energetic.
If the pregnancy terminates, especially in the early stages, due to resorbtion or other factors, the spit test can give an ambiguous result as to whether she is still pregnant or doesn’t have a mature follicle. Not being able to tell which is true, you would need to re-test 3 days later in order to make a determination.
So, ideally you would spit test at 7 days, 10 days, 14 days and then weekly until you are able to use the Preg-Tone at 30-40 days. Then use the Preg-Tone through out the remainder of the pregnancy–very clean, very accurate and not much work. Also, if the female slips the pregnancy you will have a much clearer idea of what is going on than with a random spit test.
Additionally, and particularly with submissive females, they may appear receptive all the time, especially to the unskilled handler. Over-breeding of females can cause uterine infections.