With the growing use of artificial insemination and frozen semen in dog breeding, the level of predictability of fertile matings for any breed of dogs, particularly with age, is largely unknown. The researchers are currently developing a database with CHF funding to determine the relationship of sperm characteristics to pregnancy outcome in a large population of Labrador Retrievers. In this follow up study, the researchers will recruit and obtain semen samples from Labrador Retriever stud dogs with a history of subfertility or infertility and evaluate a wide array of routine and advanced semen quality measures including sperm viability, motility, lipid peroxidation, oxidative metabolism, acrosomal integrity, sperm chromatin structure assay (SCSA), mitochondrial DNA, and reactive oxygen species generation. The two databases will be compared using a powerful epidemiological approach to determine sperm effects on fertility. The relationship of sperm factors and male age to pregnancy will be measured. This project will result in improved accuracy to predict fertility for valuable stud dogs, and improve analysis of transported and frozen semen for Labrador Retrievers that will likely benefit all breeds.