title: Heterogeneity of sperm nuclear chromatin structure and its relationship to bull fertility.
abstract: The relationship between sperm nuclear chromatin structure and fertility was evaluated in two groups of Holstein bulls: Group 1, 49 mature bulls, and Group 2, 18 young bulls. Fertility ratings had been estimated for Group 1 and nonreturn rates were known for Group 2. Semen samples were measured by the sperm chromatin structure assay (SCSA): sperm were treated to induce partial in situ DNA denaturation, stained with acridine orange, and evaluated by flow cytometry. Acridine orange intercalated into double-stranded DNA emits green fluorescence upon excitation with 488 nm light, and red fluorescence when associated with single-stranded DNA. An index of DNA denaturation per cell is provided by alpha-t [alpha t = red/(red + green) fluorescence]. The standard deviation (SD alpha t), coefficient of variation (CV alpha t) and proportion of cells outside the main population (COMP alpha t) of the alpha t distribution quantify the extent of denaturation for a sample. Intraclass correlations of the alpha t values were high (greater than or equal to 0.70), based on four collections obtained over several years from Group 1 bulls. Negative correlations were obtained between fertility ratings and both SD alpha t (-0.58, p less than 0.01) and COMP alpha t (-0.40, p less than 0.01) in Group 1, and between nonreturn rates and both SD alpha t (-0.65, p less than 0.01) and COMP alpha t (-0.53, p less than 0.05) in Group 2. These data suggest that the SCSA will be of value for identification of low fertility sires and poor quality semen samples.
mesh_terms: D000375:Aging; D000704:Analysis of Variance; D000818:Animals; D002417:Cattle; D002467:Cell Nucleus / Q000648:ultrastructure*; D002843:Chromatin / Q000648:ultrastructure*; D005298:Fertility; D005434:Flow Cytometry; D008297:Male; D013094:Spermatozoa / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D002843:Chromatin