title: Changeability of sperm chromatin structure during liquid storage of ovine semen in milk-egg yolk- and soybean lecithin-based extenders and their relationships to field-fertility.
abstract: The aim of this experiment was to study the effect of semen extender on sperm chromatin structure and to correlate chromatin integrity with field-fertility of preserved ram semen. Ejaculates of at least 2 × 10(9) sperm/ml and 70 % progressive motility were collected using an artificial vagina from Chios rams (n = 11, 4-6 years old), split-diluted to 1 × 10(9) sperm/ml with milk-egg yolk- and soybean lecithin (Ovixcell®)-based extenders, packaged in 0.5-ml straws and examined after 6, 24 and 48 h of storage at 5 ± 1 °C. Evaluation endpoints were computer-assisted sperm motion analysis, fluorescence-based analysis of chromatin structure by chromomycin A3 and acridine orange assays, and 65-day pregnancy rate (PR) of 34- to 36-h preserved semen after intra-cervical insemination of ewes (n = 154) in progestagen-synchronized estrus. Neither extender nor storage time had any influence on incidence of decondensed chromatin. Unlike Ovixcell® extender, deterioration of sperm motility (P < 0.01) and chromatin stability (P < 0.005) was detected after 48 h of storage in milk-egg yolk extender. Sperm motility accounted for 14.4-18.5 % of variations in chromatin integrity (P < 0.001). No significant difference was found in PR of Ovixcell®- and milk-egg yolk-stored semen. Nevertheless, PR differed between rams (14.3-71.4 %; P < 0.025). Chromatin integrity explained 10.2-56.3 % of variations in PR (P < 0.05-0.01). A pronounced decline in PR (19.1 %) was observed when percentages of decondensed and destabilized chromatin have reached thresholds of 10.5-30 % and 4-9 %, respectively. In conclusion, Ovixcell® is superior to milk-egg yolk extender in preserving chromatin stability and motility. Chromatin defects are negatively associated with sperm fertility.
authors.affiliation: EquiBiotech Inc-Research Services in Farm Animal Breeding, 19 Gravias street, 54645, Thessaloniki, Greece, drtarekkhalifa@gmail.com.
authors.forename: Tarek
authors.initials: T
authors.lastname: Khalifa
authors.forename: Aristotelis
authors.initials: A
authors.lastname: Lymberopoulos
mesh_terms: D000818:Animals; D002843:Chromatin / Q000378:metabolism*; D016001:Confidence Intervals; D004530:Egg Yolk / Q000737:chemistry*; D005260:Female; D005298:Fertility / Q000187:drug effects; D054709:Lecithins / Q000494:pharmacology*; D008297:Male; D008892:Milk / Q000737:chemistry*; D016017:Odds Ratio; D011247:Pregnancy; D012661:Semen / Q000378:metabolism*; D012662:Semen Preservation / Q000379:methods*; D012756:Sheep; D013025:Glycine max / Q000737:chemistry; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000378:metabolism*
chemical_list: D002843:Chromatin; D054709:Lecithins