This study was conducted to assess the regulation of glycolysis by 6phosphofructokinase (PFK) during the postmortem metabolism of beef muscle. In the first experiment, M. sternocephalicus pars mandibularis samples were excised from six randomly-selected steers. Two samples were obtained from each steer immediately postmortem; one sample was quickly immersed in liquid nitrogen and the other was stored at 4oC for 4 d. Glycogen concentrations decreased 45% from d 0 to d 4, and 39.6 ?mol/g of glycogen was still present in the tissue at d 4. Concentrations of free glucose increased (P < 0.001) from 0.84 ?mol/g at d 0 to 6.54 ?mol/g at d 4. Fructose-6-phosphate (F6P) and glucose-6-phosphate (G6P) increased (P < 0.001) from d 0 to d 4 (2.8-fold and 4.7-fold, respectively). Lactate began accumulating immediately (3.33 ?mol/g) and was elevated to 45.9 ?mol/g by d 4. Glycolytic potential was 34.4 ?mol/g higher (P < 0.05) when measured at d 0 than at d 4. The greatest activity of PFK was measured in fresh muscle extracts, between pH 7.4-7.8; by reducing the pH to 7.0, PFK activity was depressed by nearly 50% at 1 mM F6P. In a second experiment, M. longissimus lumborum samples were excised at the 13th thoracic rib location from six randomly-selected steers. Samples were obtained at intervals ranging from 40 min to 24 h postmortem. Glycogen concentrations decreased 45% between 40 and 100 min, and tended (P &#8804; 0.10) to decrease between 100 min and 24 h (from 47 to 32 ?mol/g). Concentrations of free glucose increased (P &#8804; 0.009) from 1.0 ?mol/g at 40 min to 5.0 ?mol/g at 24 h. Concentrations of F6P and G6P increased dramatically after 100 min (muscle pH &#8804; 6.5), whereas glycogen depletion appeared to halt by 100 min. Lactate began accumulating almost immediately and tripled in concentration by 24 h. The elevation of G6P and F6P, coupled with the pH sensitivity of PFK, indicate that the postmortem decline in pH ultimately inactivates PFK prior to glycogen depletion.

Bovine preimplantation embryos derived from nuclear transfer experiments exhibit a global state of genomic hypermethylation that likely account for the large number of developmental abnormalities observed to date. The central hypotheses of this work is that the genomic hypermethylation and improper epigenetic reprogramming reported in studies of bovine nuclear transfer, are in large part due to abnormal expression and regulation of the DNA methyltransferase proteins. Bovine Dnmt mRNAs display strong sequence homology to those of human and mouse and similar to other species, exist as multiple isoforms. Two of these splice variants, which have been termed Dnmt2&#947; and Dnmt3a4 represent previously unreported sequence combinations. Investigation of bovine DNA methyltransferase expression in the bovine oocyte and early preimplantation development has revealed an intricate system divergent from observations previously reported in the mouse. Specifically, the somatic version of Dnmt1 along with Dnmt2, 3a and 3b are all expressed during these initial stages of bovine development. Further, real time analyses of the Dnmt transcripts in cloned and in vitro produced embryos reveal significant differences in the mRNA expression levels of Dnmt1 and 2 but not Dnmt3a and 3b suggesting that the de novo methyltransferases may be functioning normally while Dnmt1 and Dnmt2 are aberrantly methylating the genome during a critical time when methylation levels should be receding. Real time PCR analysis of the Dnmt transcripts in fetal and adult tissues has revealed a developmental and tissue specific expression pattern suggesting that proper expression and function of these enzymes is a key element in the process of differentiation. These results are further supported by studies of Dnmt expression in aging bovine fibroblast cultures, which suggest that the Dnmts may play some as yet unidentified role in cellular senescence. Recently, it has been postulated that the cause of abnormal methylation observed in cloned embryos may be due in part to misexpression of the Dnmt1o isoform during preimplantation development. Work presented here raises new and significant hypotheses that must be considered both regarding the cadre of DNA methyltranferases that direct epigenetic programming during normal development and regarding the implication of abnormal DNMT expression in cloned embryos. Bovine preimplantation embryos derived from nuclear transfer experiments exhibit a global state of genomic hypermethylation that likely account for the large number of developmental abnormalities observed to date. The central hypotheses of this work is that the genomic hypermethylation and improper epigenetic reprogramming reported in studies of bovine nuclear transfer, are in large part due to abnormal expression and regulation of the DNA methyltransferase proteins. Bovine Dnmt mRNAs display strong sequence homology to those of human and mouse and similar to other species, exist as multiple isoforms. Two of these splice variants, which have been termed Dnmt2&#947; and Dnmt3a4 represent previously unreported sequence combinations. Investigation of bovine DNA methyltransferase expression in the bovine oocyte and early preimplantation development has revealed an intricate system divergent from observations previously reported in the mouse. Specifically, the somatic version of Dnmt1 along with Dnmt2, 3a and 3b are all expressed during these initial stages of bovine development. Further, real time analyses of the Dnmt transcripts in cloned and in vitro produced embryos reveal significant differences in the mRNA expression levels of Dnmt1 and 2 but not Dnmt3a and 3b suggesting that the de novo methyltransferases may be functioning normally while Dnmt1 and Dnmt2 are aberrantly methylating the genome during a critical time when methylation levels should be receding. Real time PCR analysis of the Dnmt transcripts in fetal and adult tissues has revealed a developmental and tissue specific expression pattern suggesting that proper expression and function of these enzymes is a key element in the process of differentiation. These results are further supported by studies of Dnmt expression in aging bovine fibroblast cultures, which suggest that the Dnmts may play some as yet unidentified role in cellular senescence. Recently, it has been postulated that the cause of abnormal methylation observed in cloned embryos may be due in part to misexpression of the Dnmt1o isoform during preimplantation development. Work presented here raises new and significant hypotheses that must be considered both regarding the cadre of DNA methyltranferases that direct epigenetic programming during normal development and regarding the implication of abnormal DNMT expression in cloned embryos.

Bacterial and fungal culturing was conducted on samples taken from the vaginal fornix of 106 cows, of which 42 had vaginitis and 64 had normal vaginas. The diagnosis of vaginitis and non-vaginitis samples was determined by histologic examination. Aerobic, anaerobic, and microaerophilic cultures were done. In addition, cultures were performed for Campylobacter sp., Ureaplasma sp., Mycoplasma sp., Tritrichomonas foetus, and fungi. All 106 samples contained mixed aerobic bacterial cultures. The more frequent aerobic isolates included Acinetobacter lwoffii, Arcanobacterium pyogenes, Escherichia coli, Corynebacterium spp., and Streptococcus spp. These organisms were isolated from both groups of cows, but more frequently from the vaginitis group. Anaerobic isolates included Peptostreptococcus spp., Prevotella spp., and Fusobacterium spp. The fungal isolates included Aspergillus sp., Mucor sp., and Penicillium sp.

Reproduction de : Thèse d'exercice : Médecine vétérinaire : Toulouse 3 : 2008. / Titre provenant de l'écran titre. Bibliogr. p. 85-86.

A method that involves analysis of bovine liver by slurry nebulization and ICP-OES has been developed. This method permits rapid and accurate determination of Cu, Fe, Mg, Mn and Zn in bovine liver. Aliquots of freeze-dried and powdered bovine liver sample were dispersed in 2.0 M HNO3 and sonicated to homogenize the resulting slurries. Bovine liver samples were also microwave digested or subjected to aqueous extraction for comparison of analytical results. Concentrations of Cu, Fe, Mg, Mn and Zn in aqueous slurries, the digests, and aqueous extracts were determined by the ICP-OES using external calibration curves. A student’s ttest showed that the results obtained using the slurry method were in good agreement at 95 % confidence level (CL) with those of microwave digestion or aqueous extraction techniques, except for Fe. To check the accuracy and precision of the slurry method, a bovine liver CRM was analyzed and good agreement was achieved with the certified values at 95 % CL. The results demonstrate inefficiency of aqueous extraction technique for complete removal of Fe in bovine liver sample.

Two clinical studies were conducted to evaluate the effects of recombinant bovine somatotropin in daily, weekly or bi-weekly injected preparations on milk yield, feed efficiency and reproduction. In the first study, a linear dose-response effect of recombinant bST on milk yield with doses of up to 150 mg &middot; 7d-1 was observed. Feed intake was not affected and feed efficiency was increased by bST during lactation. Body condition at the end of lactation was lower in cows supplemented with bST. Feed intake during the dry period following bST supplementation was not affected by bST given during lactation. When differences in body condition were taken into account, efficiency of conversion of dietary energy to milk energy was not affected by bST supplementation. In another study of bST supplementation during lactation, a daily dose of 10.3 mg &middot; d-1 and a sustained release formulation of 350 mg &middot; 14d-1 did not increase milk production or feed efficiency. In the absence of a milk production response, reproductive performance was not affected by bST supplementation. Progesterone production in the second oestrous cycle post partum was higher in cows receiving bST but oestrous activity was not affected. Body condition at calving did not affect milk production, response to rbST or reproductive performance. Cows calving with a body condition less than 3.25 consumed more feed per unit of body weight and resumed ovarian cyclic activity later than cows calving with a body condition greater or equal to 3.25. An epinephrine challenge during the dry period was performed to evaluate whether the effects of bST supplementation during lactation on adipose tissue metabolism persisted during the dry period. Lipid mobilisation by cows having received bST during lactation, as described by the release of non-esterified fatty acids following the epinephrine challenge, did not differ from control cows. Two studies designed to evaluate the effect of bST on oestradiol-induce

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