The single most important factor in determining the sperm quality of a dog is the sperm cells ability to swim in a straight line, a term called Progressive Motility.
The PetCount Sperm Quality Test for dogs measures the number of Progressive Motile Sperm Cells, also called PMSCs.
"The semen factors thought to be most important to fertility are the motility, the number and the morphology of the spermatozoa. There is a direct relationship between sperm production by the testes and testicular size. Therefore, larger dogs have higher sperm counts than smaller dogs. It has been reported that there is a relationship between sperm count and body weight. This may be true for animals in good body condition, but the relationship is lost in obese animals because testicular size does not increase. Even among breeds of similar size, there are variations in sperm counts." Johnson CA, Reproductive System Disorders. In: Nelson RW and Couto CG (eds) Small Animal Internal Medicine 4th edition. St. Louis, Elsevier.
At least 70% of a dog's sperm sample should have a rapid, steady forward progression. A “normal” dog should have a minimum of 210 million Progressive Motile Sperm Cells (PMSCs)/ml based on a total count of minimum 300 million sperm cells per ml.
The threshold value always needs to be taken with a grain of salt. It only takes one “lucky” sperm cell to fertilize an egg. Meaning the suggested 210 million PMSC is a rough Ball Park figure and should not be seen as the final number. You would clearly see dogs with lower PMSCs who can make puppies and vice versa.