Suplementos minerais quelatados para vacas nelores a pasto : dinâmica folicular, qualidade oocitária, desenvolvimento embrionário e estresse oxidativo

Abstract

The present study was to evaluate whether supplementation with chelated minerals (copper, zinc and selenium) for Nellore cows grazing alters the oocyte quality, level of oxidative stress and early development of embryos produced. The experiment was conducted in Cuiabá-MT, during the months April to July 2009. We used 24 adult Nellore with age and mean weights of the initial 36 months, 395 kg and mean body condition score of 4.8 were randomly divided into two groups: control group (CG, supplemented with conventional mineral) and supplemented group ( GS, animals supplemented with zinc, copper and selenium chelated). Each group was kept in paddocks of Brachiaria brizantha cv Marandu received 1 kg concentrate per animal per day. Chelated mineral supplementation was performed during a period of 99 days. During the experimental period were two follicular aspirations, one to 59 days and another at 99 days of supplementation. Fortnightly and the day of aspiration when the animals were evaluated for their weight and body condition score (BCS). The oocytes were immediately assessed and classified as Grade I (good), Grade II (good), Grade III (regular), Grade IV (poor), atretic (bad) and degenerated (dead) according to their morphology and quality , and pooled into two groups: viable (grades I and II) and nonviable (grades III, IV, atretic and degenerate). In follicular fluid was measured the level of oxidative stress by determining the concentration of thiobarbituric acid reactive substances (TBARS). The experiment was completely randomized and data were analyzed by ANOVA with significance level of 10%. There was no effect (p> 0.10) of supplementation with chelated minerals on the number of non-viable oocytes (p = 0.3773). Moreover, an interaction effect (p = 0.0816) between collection and add to ECC, weight (p = 0.0253) and number of viable oocytes (p = 0.0365) in this last variable when analyzed separately collections could not demonstrate the effect of supplementation (p> 0.10). There was no effect (p> 0.10) of supplementation with chelated minerals on the percentage of cleaved oocytes, total embryos produced, percentage of embryos, cells in the morula stage, embryos in blastocyst stage embryos and expanded blastocyst stage in 6 days of cultivation.Moreover, differences were observed (p <0.10) between supplements to the level of oxidative stress measured in follicular fluid (TBARS 0.003099 ± 1.1141 X10-5 and 0.003094 ± 9.7251 x 10 - 6 ng / mL, for GC and GS, respectively). Oral supplementation with minerals zinc, copper and selenium in the form of chelates, the levels used did not affect the parameters of early embryonic development, but provided for ECC effect, weight, total number of oocytes aspirated and viable level of oxidative stress Nelore cows.