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

Department of Animal Sciences, University of Florida, Gainesville, 32611-0910, USA.
Journal of Dairy Science (Impact Factor: 2.57). 05/2003; 86(4):1194-200. DOI: 10.3168/jds.S0022-0302(03)73703-5
Source: PubMed


Feeding cattle diets high in degradable crude protein (CP) or in excess of requirements can reduce fertility and lower uterine pH. Objectives were to determine direct effects of urea and acidic pH during oocyte maturation and embryonic development. For experiment 1, oocytes were matured in medium containing 0, 5, 7.5, or 10 mM urea (0, 14, 21, or 28 mg/dl urea nitrogen, respectively). Cleavage rate was not reduced by any concentration of urea. However, the proportion of oocytes developing to the blastocyst stage at d 8 after insemination was reduced by 7.5 mM urea. In addition, the proportion of cleaved oocytes becoming blastocysts was decreased by 5 and 7.5 mM urea. For experiment 2, putative zygotes were collected -9 h after insemination and cultured in modified Potassium Simplex 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 nonmetabolizable acid, was used to decrease culture 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 concentrations. Results support the idea that feeding diets rich in highly degradable CP compromises fertility through direct actions of urea on the oocyte and through diet-induced alterations in uterine pH.

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    • "The combination of high dietary energy and increased urea concentration exacerbates the deleterious effects of urea alone on embryo development (Papadopoulos et al. 2001). Similarly, in cattle, in vivo exposure to high levels of ammonia or urea inhibited oocyte capacity to develop to blastocysts in vitro (Sinclair et al. 2000; Ferreira et al. 2011) and likely also has a negative effect on oocyte potential through acidification of uterine pH (Ocon and Hansen 2003). Embryos derived from a maternal environment with high concentrations of urea show compromised long-term potential with reduced pregnancy rate after transfer (Rhoads et al. 2006). "
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    ABSTRACT: Maternal periconceptional (PC) nutrition, coupled with maternal physiological condition, can impact on reproductive performance and potential across mammalian species. Oocyte quality and embryo development are affected adversely by either nutrient restriction or excess. Moreover, the quality of maternal PC nutrition can have lasting effects through fetal development and postnatally into adulthood. Chronic disease, notably cardiovascular and metabolic disease, and abnormal behaviour have been identified in adult offspring in small and large animal models of PC nutrient restriction. These long-term effects associate with compensatory responses that begin from the time of early embryo development. This review assesses the field of PC nutrition in vivo on short- and long-term developmental consequences in rodent and ruminant models and considers the implications for human health.
    Full-text · Article · Dec 2011 · Reproduction Fertility and Development
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    • "Collectively, these reports prompted a different approach to the question, since deleterious effects of high-protein diets were traditionally associated with changes in uterine environment [5] [7] [12], rather than on the oocyte per se. In vitro studies corroborated this hypothesis; decreases in the rate of blastocyst formation due to the presence of urea during IVM [10], to ammonia added in IVC medium [13], as well as impairment in meiosis in oocytes matured in vitro in the presence of urea [14], have been reported. Since short-term urea feeding without an adaptation period was associated with a decrease in embryos recovered from superovulated dairy cows [15], in the present study we tested the hypothesis that a sudden increase in PUN is associated with decreased oocyte quality in non-lactating beef heifers. "
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    ABSTRACT: Cows fed high-protein diets may have impaired reproductive performance. Although the pathogenesis has not been completely elucidated, it appears that not only the uterus, but also the follicle and oocyte, are affected by excessive plasma urea nitrogen (PUN) concentrations. Thus, the objective was to determine the effects of short-term urea feeding on the competence of bovine oocytes. Forty crossbred heifers (Bos indicus vs Bos taurus) were allocated to two groups, namely CONTROL (maintenance diet) and UREA (maintenance diet supplemented with 75 g of urea/day), following a cross-over design. Heifers received their respective diets for 6 d (without adaptation). On the sixth day, blood samples were harvested both before and 3 h after feeding, and cumulus oocyte complexes (COCs) were collected by ovum pick-up. Although PUN concentrations were higher in UREA than CONTROL heifers (31.31 mg/dL ± 1.13 vs 22.12 mg/dL ± 0.86; mean ± SEM), neither the number of COCs recovered (8.8 ± 1.0 vs 9.2 ± 0.8, UREA vs CONTROL, respectively) nor their quality (based on morphology) differed significantly between groups. Next, oocytes were fertilized and cultured in vitro to assess developmental rates. There was an absence of significant differences between groups for rates of cleavage (Day 3) or blastocyst formation (Days 6, 7 and 9), but the hatched blastocyst rate on Day 11 after fertilization was lower (P < 0.05) in the UREA than the CONTROL groups (64.3 vs 83.5%). Therefore, we inferred that the effects of urea were only manifest later in development. In conclusion, high PUN concentrations decreased oocyte competence in heifers, reinforcing the hypothesis that poor reproductive performance in cows with high PUN was due, at least in part, to a deleterious effect on oocytes.
    Full-text · Article · Jul 2011 · Theriogenology
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    • "However, in these studies no concentration gradients between serum and FF were mentioned, there is now enough evidence to conclude that the growing and maturing oocyte is directly exposed to the typical biochemical changes that occur in highyielding dairy cows early post partum. It has furthermore been established that high urea concentrations, also found in FF (Hammon et al., 2005), can be toxic to oocytes during maturation (Ocon and Hansen, 2003; Iwata et al., 2006), probably through an inhibition of the polymerization of tubulin into microtubules (De Wit et al., 2001). The same is true for the lowered glucose concentrations observed. "
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    ABSTRACT: Unsatisfactory reproductive performance in dairy cows, such as reduced conception rates, in addition to an increased incidence of early embryonic mortality, is reported worldwide and has been associated with a period of negative energy balance (NEB) early post partum. Typically, NEB is associated with biochemical changes such as high non-esterified fatty acid (NEFA), high β-hydroxybutyrate (β-OHB) and low glucose concentrations. The concentrations of these and other metabolites in the follicular fluid (FF) of high-yielding dairy cows during NEB were determined and extensively analyzed, and then were replicated in in vitro maturation models to investigate their effect on oocyte quality. The results showed that typical metabolic changes during NEB are well reflected in the FF of the dominant follicle. However, the oocyte seems to be relatively isolated from extremely elevated NEFA or very low glucose concentrations in the blood. Nevertheless, the in vitro maturation models revealed that NEB-associated high NEFA and low glucose levels in the FF are indeed toxic to the oocyte, resulting in deficient oocyte maturation and developmental competence. Induced apoptosis and necrosis in the cumulus cells was particularly obvious. Furthermore, maturation in saturated free fatty acid-rich media had a carry-over effect on embryo quality, leading to reduced cryotolerance of day 7 embryos. Only β-OHB showed an additive toxic effect in moderately hypoglycemic maturation conditions. These in vitro maturation models, based on in vivo observations, suggest that a period of NEB may hamper the fertility of high-yielding dairy cows through increased NEFA and decreased glucose concentrations in the FF directly affecting oocyte quality. In addition to oocyte quality, these results also demonstrate that embryo quality is reduced following an NEB episode. This important observation may be linked to the typical diet provided to stimulate milk yield, or to physiological adaptations sustaining the high milk production. Research into this phenomenon is ongoing.
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