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: 2.55). 05/2003; 86(4):1194-200. DOI: 10.3168/jds.S0022-0302(03)73703-5
Source: PubMed

ABSTRACT 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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: During early postpartum, high-producing dairy cows undergo a period of extensive tissue catabolism because of negative nutrient balance. Homeorrhetic controls assure that nutrients are partitioned to favor lactation at the same time that homeostasis secures survival. However, unrestrained metabolic disturbances often lead to diseases which, in turn, dramatically decrease both productive and reproductive performance. Negative nutrient balance has been associated with compromised immune and reproductive functions in dairy cows. Low circulating concentrations of glucose and insulin associated with elevated concentrations of non-esterified fatty acids and ketone bodies postpartum have disruptive and detrimental effects on the oocyte, granulosa and immune cells. Negative nutrient balance is associated with changes in the pattern of ovarian follicle growth which can indirectly affect oocyte quality. Some of this disruption seems to be the result of endocrine and biochemical changes that alter the micro-environment of the growing and maturing oocyte. In addition, cows under negative nutrient balance have extended periods of anovulation. Postpartum anestrus, as well as infertility, is magnified by losses of body condition during the early postpartum period. The underlying mechanism for resumption of ovulatory cycles seems to be associated with metabolic signals and regulatory hormones primarily insulin and insulin-like growth factor (IGF)-1, which link nutritional status with gonadotropin secretion, recoupling of the growth hormone-IGF system, and follicle maturation and ovulation. Feeding diets that promote increases in plasma glucose and insulin may improve the metabolic and endocrine status of cows in early lactation. Furthermore, fertility in postpartum cows is also determined by uterine health. Reductions in circulating concentrations of Ca and antioxidant vitamins around parturition are also linked with impaired immune competence and result in greater risk of uterine diseases that impair reproduction. Specific nutrients and dietary ingredients have been implicated to affect reproduction in cattle. Excess intake of dietary protein has been suggested as detrimental to fertility, although feeding excess of dietary protein can no longer be justified. Addition of moderate amounts of supplemental fat to the diet improves caloric intake, modulates prostaglandin F2 secretion by the uterus, affects ovarian dynamics, enhances luteal function and embryo quality, and has moderate positive effects on fertility. More specifically, some fatty acids might impact fertilization rate and embryo quality in dairy cows. On the contrary, some dietary ingredients, such as gossypol, when ingested in large quantities decrease fertility of dairy cows because of its negative effects on embryo quality and pregnancy maintenance.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Lactating dairy cows (n=177) feed with grass and corn silage ad libitum kept in pasture, were randomly assigned to evaluate how urea nitrogen in plasma and milk can be related to their pregnancy rate. Blood and milk samples were collected on the artificial insemination (AI) day to evaluate plasma urea nitrogen (PUN) and milk urea nitrogen (MUN) as well as progesterone levels, excluding cows with progesterone higher than 0.5 ng/ml. Cows were considered pregnant if six weeks after artificial insemination, they did not return to estrus. Concentrations of PUN or MUN greater than the average (16 mg/dl) were associated with decreased pregnancy rates (13% and 14%, respectively) (p< 0.05) as compared to the cows with urea levels less than this value on the insemination day. As PUN and MUN increased to greater than 16 mg/dl, the likelihood ratio for pregnancy decreased. There was a high correlation between PUN and MUN concentrations (r2= 0.97, p≤ 0.001). The results of this study indicate that an increase in PUN or MUN can exert direct or indirect effects in reproduction, impairing the conception of grazing dairy cows.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The objectives of the present study were to investigate the effects of dietary urea supplementation (1.0% and 3.0%) on oocytes quality, timing expected of embryo cleavages, offspring numbers and weights, blood components and rectal temperature in mice. Sixty of growing albino mice were classified into three groups; the control group was given basal control diet and the other two groups were fed on basal control diet supplemented with 1.0% and 3.0% urea. Body weights were recorded at the beginning and after 5 weeks. Thereafter, five female mice of each group were injected with 7.5 IU of pregnant mare serum gonadotropin (PMSG) for determination of oocyte quality after 48h of injection. The fifteen female mice of each group were injected with 7.5 IU of PMSG followed by 7.5 IU of human chorionic gonadotropin (hCG) after 48h and mated with males of proven fertility. Five mated females of each group were used for determination of embryo cleavages to four cell stage and the other five mated females were used for determination of embryo cleavages to eight cell stage upon 59-60 and 70 h of hCG injection, respectively. Rectal temperatures were recorded and blood samples were collected. The remaining five mated females of each group were left for parturition. The offspring number, litter size and male:female ratio were recorded. Hematocrit and hemoglobin concentrations were determined in blood whereas urea, total protein, albumin, glucose calcium and phosphorus concentrations were determined in plasma. The results indicated that offspring number and weight of litter size at birth were significantly (P<0.05) increased in the urea groups compared to control group. Percentage of good quality oocytes was high (70%) in control group compared to 3% urea group (60%). Dietary 3% urea was delayed cleavages to four-cell stage embryos at the expected time. Dietary urea was significantly (P<0.05) increased concentrations of hematocrit and hemoglobin in blood and urea, total protein, globulin, glucose, potassium and phosphorus in plasma. In conclusions, although 3% dietary urea decreased oocytes quality and timing expected of embryo cleavages to four cell stages, it increased significantly (P<0.05) offspring number and weight of litter size.

Preview (2 Sources)

Available from