Article

Disruption of Bovine Oocytes and Preimplantation Embryos by Urea and Acidic pH1

Department of Animal Sciences, University of Florida, Gainesville, 32611-0910
Journal of Dairy Science - J DAIRY SCI 01/2003; 86(4):1194-1200. DOI: 10.3168/jds.S0022-0302(03)73703-5

ABSTRACT Feeding cattle diets high in degradable crude pro- tein(CP)orinexcessofrequirementscanreducefertil- ityandloweruterine pH.Objectivesweretodetermine direct effects of urea and acidic pH during oocyte mat- uration and embryonic development. For experiment 1, oocytes were matured in medium containing 0, 5, 7.5,or10mMurea(0,14,21,or28mg/dlureanitrogen, respectively). Cleavage rate was not reduced by any concentration of urea. However, the proportion of oo- cytes developing to the blastocyst stage at d 8 after insemination was reduced by 7.5 mM urea. In addi- tion, the proportion of cleaved oocytes becoming blas- tocysts was decreased by 5 and 7.5 mM urea. For ex- periment 2, putative zygotes were collected ∼ 9ha fter inseminationandculturedinmodifiedPotassiumSim- plex Optimized Medium (KSOM). Urea did not reduce the proportion of oocytes developing to the blastocyst stage, although 10 mM urea reduced cleavage rate slightly. For experiment 3, dimethadione (DMD), a weak nonmetabolizableacid, was used todecrease cul- ture medium pH. Putative zygotes were cultured in modified KSOM containing 0, 10, 15, or 20 mM DMD for 8 d. DMD reduced cleavage rate at 15 and 20 mM and development to the blastocyst stage at all concen- trations. Results support the idea that feeding diets rich in highly degradable CP compromises fertility through direct actions of urea on the oocyte and

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