Relationship among seminal quality measures and field fertility of young dairy bulls using low-dose inseminations

Optimal use of genetically superior bulls through artificial insemination (AI) is highly dependent on precise assessment of seminal quality which allows for reasonable estimations of field fertility with normal or low-dose inseminations. In the present study, seminal measures such as sperm motility and morphology, sperm viability, sperm DNA fragmentation, and the ability of the sperm to display an acrosome reaction were tested. The relationships between field fertility and the seminal measures were investigated using 3 ejaculates from each of 195 bulls (156 Holstein and 39 Jersey) participating in a progeny test program. A range of AT closes, varying from 2 x 10(6) to 15 x 10(6) sperm/straw, was obtained by a controlled dilution process applied to each ejaculate. The different AT doses were distributed at random among 75,610 experimental first inseminations in 4,721 herds and 208 AI technicians. Most of the seminal measures appeared to contain a predictive value for the nonreturn to estrus at 56 d post-AI (NRR56) regardless of the number of sperm per AT dose and can be regarded as noncompensable sperm traits. But, due to correlations between the individual measures, the best model for describing (and predicting) NRR56 was based on sperm concentration and viability in the neat (raw) semen, and post-thaw sperm viability. The statistical models for describing NRR56 included the following explanatory variables: strength of the estrus, number of sperm per AI dose, breed, parity, and random components representing herds and AI technicians. The present results show that the most precise estimation of a bull's NRR56 can be achieved through flow cytometric detection of sperm concentration and viability in neat semen as well as flow cytometric detection of post-thaw sperm viability.