PubMed Health⌕ Search

Biomedical subjects

Y Sun

Publications and source records attributed to Y Sun.

At least 415 records · Page 23Linked to original sources
PubMed1999

Determinants of neutralization resistance in the envelope glycoproteins of a simian-human immunodeficiency virus passaged in vivo.

In vivo passage of a simian-human immunodeficiency virus (SHIV-89.6) generated a virus, SHIV-89.6P, that exhibited increased resistance to some neutralizing antibodies (G. B. Karlsson et al., J. Exp. Med. 188:1159-1171, 1998). Here we examine the range of human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies to which the passaged virus became resistant and identify envelope glycoprotein determinants of antibody resistance. Compared with the envelope glycoproteins derived from the parental SHIV-89.6, the envelope glycoproteins of the passaged virus were resistant to antibodies directed against the gp120 V3 variable loop and the CD4 binding site. By contrast, both viral envelope glycoproteins were equally sensitive to neutralization by two antibodies, 2G12 and 2F5, that recognize poorly immunogenic structures on gp120 and gp41, respectively. Changes in the V2 and V3 variable loops of gp120 were necessary and sufficient for full resistance to the IgG1b12 antibody, which is directed against the CD4 binding site. Changes in the V3 loop specified complete resistance to a V3 loop-directed antibody, while changes in the V1/V2 loops conferred partial resistance to this antibody. The epitopes of the neutralizing antibodies were not disrupted by the resistance-associated changes. These results indicate that in vivo selection occurs for HIV-1 envelope glycoproteins with variable loop conformations that restrict the access of antibodies to immunogenic neutralization epitopes.

Animals↗
PubMed1999

Comparison of immunity generated by nucleic acid-, MF59-, and ISCOM-formulated human immunodeficiency virus type 1 vaccines in Rhesus macaques: evidence for viral clearance.

The kinetics of T-helper immune responses generated in 16 mature outbred rhesus monkeys (Macaca mulatta) within a 10-month period by three different human immunodeficiency virus type 1 (HIV-1) vaccine strategies were compared. Immune responses to monomeric recombinant gp120SF2 (rgp120) when the protein was expressed in vivo by DNA immunization or when it was delivered as a subunit protein vaccine formulated either with the MF59 adjuvant or by incorporation into immune-stimulating complexes (ISCOMs) were compared. Virus-neutralizing antibodies (NA) against HIV-1SF2 reached similar titers in the two rgp120SF2 protein-immunized groups, but the responses showed different kinetics, while NA were delayed and their levels were low in the DNA-immunized animals. Antigen-specific gamma interferon (IFN-gamma) T-helper (type 1-like) responses were detected in the DNA-immunized group, but only after the fourth immunization, and the rgp120/MF59 group generated both IFN-gamma and interleukin-4 (IL-4) (type 2-like) responses that appeared after the third immunization. In contrast, rgp120/ISCOM-immunized animals rapidly developed marked IL-2, IFN-gamma (type 1-like), and IL-4 responses that peaked after the second immunization. To determine which type of immune responses correlated with protection from infection, all animals were challenged intravenously with 50 50% infective doses of a rhesus cell-propagated, in vivo-titrated stock of a chimeric simian immunodeficiency virus-HIVSF13 construct. Protection was observed in the two groups receiving the rgp120 subunit vaccines. Half of the animals in the ISCOM group were completely protected from infection. In other subunit vaccinees there was evidence by multiple assays that virus detected at 2 weeks postchallenge was effectively cleared. Early induction of potent type 1- as well as type 2-like T-helper responses induced the most-effective immunity.

AIDS Vaccines↗
PubMed1999

SAG, a novel zinc RING finger protein that protects cells from apoptosis induced by redox agents.

SAG (sensitive to apoptosis gene) was cloned as an inducible gene by 1,10-phenanthroline (OP), a redox-sensitive compound and an apoptosis inducer. SAG encodes a novel zinc RING finger protein that consists of 113 amino acids with a calculated molecular mass of 12.6 kDa. SAG is highly conserved during evolution, with identities of 70% between human and Caenorhabditis elegans sequences and 55% between human and yeast sequences. In human tissues, SAG is ubiquitously expressed at high levels in skeletal muscles, heart, and testis. SAG is localized in both the cytoplasm and the nucleus of cells, and its gene was mapped to chromosome 3q22-24. Bacterially expressed and purified human SAG binds to zinc and copper metal ions and prevents lipid peroxidation induced by copper or a free radical generator. When overexpressed in several human cell lines, SAG protects cells from apoptosis induced by redox agents (the metal chelator OP and zinc or copper metal ions). Mechanistically, SAG appears to inhibit and/or delay metal ion-induced cytochrome c release and caspase activation. Thus, SAG is a cellular protective molecule that appears to act as an antioxidant to inhibit apoptosis induced by metal ions and reactive oxygen species.

Amino Acid Sequence↗
PubMed1999

Regulation of AUF1 expression via conserved alternatively spliced elements in the 3' untranslated region.

The A+U-rich RNA-binding factor AUF1 exhibits characteristics of a trans-acting factor contributing to the rapid turnover of many cellular mRNAs. Structural mapping of the AUF1 gene and its transcribed mRNA has revealed alternative splicing events within the 3' untranslated region (3'-UTR). In K562 erythroleukemia cells, we have identified four alternatively spliced AUF1 3'-UTR variants, including a population of AUF1 mRNA containing a highly conserved 107-nucleotide (nt) 3'-UTR exon (exon 9) and the adjacent downstream intron (intron 9). Functional analyses using luciferase-AUF1 3'-UTR chimeric transcripts demonstrated that the presence of either a spliceable or an unspliceable intron 9 in the 3'-UTR repressed luciferase expression in cis, indicating that intron 9 sequences may down-regulate gene expression by two distinct mechanisms. In the case of the unspliceable intron, repression of luciferase expression likely involved two AUF1-binding sequences, since luciferase expression was increased by deletion of these sites. However, inclusion of the spliceable intron in the luciferase 3'-UTR down-regulated expression independent of the AUF1-binding sequences. This is likely due to nonsense-mediated mRNA decay (NMD) owing to the generation of exon-exon junctions more than 50 nt downstream of the luciferase termination codon. AUF1 mRNA splice variants generated by selective excision of intron 9 are thus also likely to be subject to NMD since intron 9 is always positioned >137 nt downstream of the stop codon. The distribution of alternatively spliced AUF1 transcripts in K562 cells is consistent with this model of regulated AUF1 expression.

Alternative Splicing↗
PubMed1999

Absence of the derived allele at the DYS199 locus in 3 NE Chinese populations.

The allelic states of DYS199 locus were studied by allele-specific PCR. We found that all of the 107 samples chosen from three populations of northeast China had DYS199 C alleles. The result excluded the possibility that this mutation first identified in native American populations came from the three populations of northeast China.

Alleles↗
PubMed1999

Expression of human apolipoprotein E reduces amyloid-beta deposition in a mouse model of Alzheimer's disease.

The epsilon4 allele of apolipoprotein E (apo E) is associated with an increased risk for developing Alzheimer's disease (AD). This may be due to interactions between apo E and the amyloid-beta protein (Abeta). To assess the effects of human apo E isoforms on Abeta deposition in vivo, we bred apo E3 and apo E4 hemizygous (+/-) transgenic mice expressing apo E by astrocytes to mice homozygous (+/+) for a mutant amyloid precursor protein (APPV717F) transgene that develop age-dependent AD neuropathology. All mice were on a mouse apo E null (-/-) background. By nine months of age, APPV717F+/-, apo E-/- mice had developed Abeta deposition, and, as reported previously, the quantity of Abeta deposits was significantly less than that seen in APPV717F+/- mice expressing mouse apo E. In contrast to effects of mouse apo E, similar levels of human apo E3 and apo E4 markedly suppressed early Abeta deposition at nine months of age in APPV717F+/- transgenic mice, even when compared with mice lacking apo E. These findings suggest that human apo E isoforms decrease Abeta aggregation or increase Abeta clearance relative to an environment in which mouse apo E or no apo E is present. The results may have important implications for understanding mechanisms underlying the link between apo E and AD.

Alzheimer Disease↗
PubMed1999

Identification of a placental-specific enhancer in the rat placental lactogen II gene that contains binding sites for members of the Ets and AP-1 (activator protein 1) families of transcription factors.

We previously identified a 3-kb proximal 5'-flanking region of the rat placental lactogen (rPLII) gene that is important for reporter gene transcription in the rat trophoblast cell line, Rcho, and targets expression to the placentas of transgenic mice. In our current studies we have used further deletion analysis and transfection studies in Rcho and GC cells to map more precisely the locations of regulatory elements involved in this placental expression. We show that sequences between - 1435 and -765 are necessary for minimal expression in Rcho cells and that there are negative regulatory elements between -3031 to -2838 and -1729 to -1435. Most importantly, we have identified a fragment between -1793 to -1729 that is essential for expression levels characteristic of the complete 3-kb 5'-region. When linked to the herpes simplex thymidine kinase minimal promoter, this fragment acts as an enhancing element in Rcho but not GC cells. Deoxyribonuclease I (DNAse I) protection and electrophoretic mobility shift assays with nuclear extracts and in vitro translated proteins identify binding sites for members of the activator protein-1 (AP-1) and Ets families of transcription factors. Site-directed mutagenesis of the individual AP-1- and Ets-binding sites leads to a partial loss of the enhancing activity; a double AP-1/Ets mutation leads to a complete loss of activity, demonstrating the functional importance of these sites. By these criteria, putative GATA-binding sites located within the enhancing fragment are not active. These new data suggest an important role for this enhancing fragment in rPLII placental giant cell expression and are the first to implicate a member of the Ets family in the regulation of this gene family.

Animals↗
PubMed1999

Essential role of biliary glycoprotein (CD66a) in morphogenesis of the human mammary epithelial cell line MCF10F.

Normal mammary epithelial cells express the cell surface protein biliary glycoprotein (BGP or CD66a) in a polarized manner, suggesting that this protein may play a role in the formation of mammary acini. In order to test this hypothesis, we interrupted the expression of BGP in the mammary epithelial line MCF10F when cultured in or on Matrigel, a source of extracellular matrix (ECM). When analyzed by immunofluorescence confocal microscopy, the BGP staining is confined to the lumenal surface and colocalizes with actin. Sequential scanning electron microscopy demonstrates that the MCF10F cells migrate to form clusters, followed by apoptotic cell death within the center, resulting in lumen formation. Transmission electron micrographs reveal the presence of tight junctions and desmosomes between the cells, microvilli along the lumenal surface, and typical apoptotic bodies within the lumen. When the MCF10F cells are transfected with the BGP antisense gene and grown in Matrigel, they exhibit reduced acini formation (12% and 20%) compared to untransfected cells (52%) or to cells transfected with vector only (62%). Acini formation is also significantly reduced when MCF10F cells grown in Matrigel are treated with anti-BGP antibody (18% at 100 microgram/ml), or recombinant soluble BGP (18% at 0.4 microM). In contrast, the BGP-negative MCF7 breast tumor cell line, which does not form acini when grown in matrigel, exhibits >60% cell death with the occasional formation of acini, when transfected with the BGP sense gene and grown in Matrigel. These results support the hypothesis that BGP plays a role in the normal differentiation program of mammary epithelial cells, indicating that its expression is essential to the formation of the lumen. Furthermore, and as shown by others, the differentiation program depends on the presence of ECM. The lack of expression of BGP in the MCF7 breast cancer cell line suggests that the downregulation of BGP expression confers a growth advantage to these cells in ECM. In addition, we found that the MCF10F cells could be separated into a BGP-positive epithelial fraction (MCF10F-e), and a BGP-negative myoepithelial fraction (MCF10F-m). When the myoepithelial cell-enriched fraction is grown on Matrigel, web-like structures are formed. These cells have a typical spindle shape cell morphology and express keratin, alpha-smooth muscle actin and vimentin, markers of the myoepithelial cell phenotype. When MCF10F-m cells are treated with IFNgamma, they express CEA (carcinoembryonic antigen) but not BGP. Since breast carcinomas, especially in situ carcinomas, express CEA, this finding may suggest a heretofore unappreciated relationship between myoepithelial cells and breast cancer.

Antigens, CD↗
PubMed1999

Deep zone articular chondrocytes in vitro express genes that show specific changes with mineralization.

We have developed a method to form reconstituted mineralized articular cartilagenous tissue in vitro from isolated deep zone chondrocytes. The aim of this study was to characterize further these cultures prior to and during mineralization. Histologic examination of the cells up to 8 days in culture showed that the chondrocytes had formed cartilagenous tissue. Similar to the in vivo cartilage, the chondrocytes expressed aggrecan, types II, I, and X collagens, osteopontin, and alkaline phosphatase (ALP). No osteocalcin mRNA expression was detected in either the in vivo cartilage or in vitro-generated tissue. Addition of beta-glycerophosphate (beta-GP) to the medium on day 5 induced mineralization and changes in gene expression. Expression of type X collagen, type II collagen, aggrecan core protein, and ALP were inhibited significantly between 2 h and 24 h after the addition of beta-GP. At 72 h, expression of these genes were still significantly depressed. These changes correlated with a decrease in collagen and proteoglycan synthesis, and ALP activity. Osteopontin expression increased within 8 h but returned to constitutive levels by 72 h. No change in type I collagen expression was detected. The changes in gene expression were not due to a direct effect of beta-GP itself, because similar gene changes occurred in the presence of phosphoethanolamine, another agent which induces mineralization. No changes in gene expression were seen in nonmineralizing cultures. In summary, articular chondrocytes grown on filter culture show expression of similar genes to the chondrocytes in the deep zone of articular cartilage and that changes in expression of specific genes were observed during tissue mineralization, suggesting that it is a suitable model to use to study the mechanism(s) regulating the localized mineralization of articular cartilage.

Aggrecans↗
PubMed1999

Detection of GB virus C/hepatitis G virus RNA by reverse-transcription polymerase chain reaction.

Recently, a novel RNA virus, designated GB virus C or hepatitis G virus (GBV-C/HGV) has been identified which may possibly be associated with human hepatitis. In this study, the nucleotide sequences of the partial nonstructural 5 (NS5) gene of GBV-C/HGV derived from sera of eight Chinese patients were determined. The overall degree of nucleotide conservation and the existence of regional highly conserved sequences make this part of the genome suitable for the development of diagnostic reagents. On the basis of sequence analysis, two sets of oligonucleotide primers were designed to establish a nested polymerase chain reaction (PCR) for detection of GBV-C/HGV RNA. The efficacy of three PCR methods (first, one stage PCR, second, nested PCR with primers from the NS5 region designed according to the prototype sequence and the third, our newly developed PCR) was compared in 133 Chinese patients with liver disease. The positive rates of these three methods were 8.3%, 11.3% and 18.0% respectively. The specificity of our PCR detecting system was verified by sequencing and restriction fragment length polymorphism (RFLP). In conclusion, because of the heterogeneity and geographic distribution character of GBV-C/HGV, it is necessary to assess the sequence variation among Chinese patients infected with GBV-C/HGV. This may allow to identify GBV-C/HGV RNA with high sensitivity and specificity.

Base Sequence↗
PubMed1999

The impact of low birth weight, perinatal conditions, and sociodemographic factors on educational outcome in kindergarten.

OBJECTIVE: To assess the relative effects and the impact of perinatal and sociodemographic risk factors on long-term morbidity within a total birth population in Florida. METHODS: School records for 339 171 children entering kindergarten in Florida public schools in the 1992-1993, 1993-1994, or 1994-1995 academic years were matched with Florida birth records from 1985 to 1990. Effects on long-term morbidity were assessed through a multivariate analysis of an educational outcome variable, defined as placement into 9 mutually exclusive categories in kindergarten. Of those categories, 7 were special education (SE) classifications determined by statewide standardized eligibility criteria, 1 was academic problems, and the reference category was regular classroom. Generalized logistic regression was used to simultaneously estimate the odds of placement in SE and academic problems. The impact of all risk factors was assessed via estimated attributable excess/deficit numbers, based on the multivariate analysis. RESULTS: Educational outcome was significantly influenced by both perinatal and sociodemographic factors. Perinatal factors had greater adverse effects on the most severe SE types, with birth weight <1000 g having the greatest effect. Sociodemographic predictors had greater effects on the mild educational disabilities. Because of their greater prevalence, the impact attributable to each of the factors (poverty, male gender, low maternal education, or non-white race) was between 5 and 10 times greater than that of low birth weight and >10 times greater than that of very low birth weight, presence of a congenital anomaly, or prenatal care. CONCLUSIONS: Results are consistent with the hypothesis that adverse perinatal conditions result in severe educational disabilities, whereas less severe outcomes are influenced by sociodemographic factors. Overall, sociodemographic factors have a greater total impact on adverse educational outcomes than perinatal factors.

Birth Weight↗
PubMed1999

Evaluation of the pancreas: a comparison of single thick-slice MR cholangiopancreatography with multiple thin-slice volume reconstruction MR cholangiopancreatography.

OBJECTIVE: The purpose of this study was to assess abilities of single thick-slice MR cholangiopancreatography and multiple thin-slice multiprojection volume reconstruction (MPVR) MR cholangiopancreatography to evaluate diseases in and around the pancreas. SUBJECTS AND METHODS: Eighty-nine patients underwent both single and MPVR MR cholangiopancreatography using a single-shot fast spin-echo technique. Image quality (five-point scale), visualization of the common bile and pancreatic ducts (three-point scale), stenotic, dilatational, or cystic changes of the pancreatic ducts, and other pathologic findings were evaluated. RESULTS: Image quality was high for single and MPVR MR cholangiopancreatography (4.1+/-0.7 and 4.5+/-0.6, respectively). Misregistration was noted in 19 patients with MPVR MR cholangiopancreatography. Ducts on and around the greater duodenal papilla and the common bile duct were revealed better using MPVR than single MR cholangiopancreatography (p < .05). Overall sensitivity, specificity, and accuracy for detection of stenosis of the main pancreatic ducts were 83.3%, 93.6%, and 88.8%, respectively, using single MR cholangiopancreatography and 76.2%, 97.9%, 87.6%, respectively, using MPVR MR cholangiopancreatography. Dilatation of the pancreatic ducts (100%) and cystic changes (n = 17 and n = 19, respectively) were well seen using either single or MPVR MR cholangiopancreatography. Although stenotic changes of the nondilated main pancreatic ducts and their branches were difficult to evaluate using single (62.5% and 14.3%, respectively) or MPVR (43.8% and 21.4%, respectively) MR cholangiopancreatography, single MR cholangiopancreatography better depicted ductal continuity. CONCLUSION: For evaluation of the pancreas, single and MPVR MR cholangiopancreatography provide complementary data; thus, we recommend using a combination of these two MR cholangiopancreatography techniques.

Adult↗
PubMed1999

Evaluation of porous collagen membrane in guided tissue regeneration.

Porous collagen membrane was prepared with collagen protein, which was extracted from bovine tendon by enzyme digestion, by freeze-drying method. The animal, clinical experiments of the membrane used in artificial dental implant system were studied. In the animal experiments, pure titanium spiral implants, which were prepared according to Adell etc. method, were implanted in the mandibular dental alveus of adult hybrid dog and covered with collagen membrane. Then the animals were killed after 4, 18 weeks individually. In the clinical research, the implants (phi 3.3 mm) were used in 33 patients of different age groups. The implant was put on the buccal lateral deficiency of implantation cavity wall, and covered with collagen membrane on the buccal lateral, then observed after 3, 6 months individually. The results of animal experiments proved the collagen membrane could guide osseous tissue regeneration around the bone integral implant which was implanted in the fresh tooth extraction fossa, be helpful to repair the fissural bone deficiency produced when implanted the implant, increase the bone content around the implant significantly, and improve the structure of new bone to a certain extent. The results of clinical research proved that collagen membrane was used in the patients with density deficiency, irregularity of alveolar ridge, or artificial dental of shorter tooth extraction, could significantly improved the bone density of artificial implant's shoulder.

Adult↗
PubMed1999

Regulation of metastasis-related gene expression by p53: a potential clinical implication.

Tumor metastasis is the main cause of mortality and treatment failure in cancer patients. It is a complex biological process regulated by alternations in expression of many genes. The p53 tumor suppressor gene has been shown to regulate expression of some metastasis-related genes. p53 transcriptionally activates expression of the genes encoding epidermal growth factor receptor, matrix metalloproteinase (MMP)-2, cathepsin D, and thrombospondin-1 but represses expression of the genes encoding basic fibroblast growth factor and multidrug resistance-1. Decreased expression of E-cadherin is associated with p53 alternations. Because these p53-regulatory genes either promote or inhibit tumor metastasis, the net effect of p53 expression on tumor metastasis depends upon the pattern of expression of these genes in a particular tumor. Because radiotherapy has been shown to increase tumor metastasis in both animal and human studies and because p53 is activated by radiation or DNA-damaging reagents, here we propose the working hypothesis that p53 may promote tumor metastasis upon induction by local radiotherapy or chemotherapy in some tumor types. For patients whose tumors contain wild-type p53, MMP inhibitors might be given with or before radiotherapy or chemotherapy to prevent an increase in tumor metastasis. Special caution should be taken with patients with cancers such as nasopharyngeal carcinoma in which p53 mutation is infrequent and radiotherapy is the main choice of treatment. To test our hypothesis, three studies are proposed and could serve as an initial step in understanding the complex biological process following radiation-induced p53 activation and its roles in regulation of tumor metastasis.

Antineoplastic Agents↗
PubMed1999

[A comparative study of HLA-A locus in northern and southern Chinese bymeans of PCR/SSOP typing].

OBJECTIVE: To compare the HLA-A locus in a population selected from Beijing (northern group) with that in a population selected from Guangzhou (southern group). METHODS: HLA typing was performed by using PCR/SSOP method. A pair of primer and 54 probes were used. RESULTS: In 18 alleles identified, the differences in gene frequency between northern and southern Chinese were found. In northern group, A*0205, 0210 and 2901 were absent, and the frequencies of A*2601, 3001 and 3101 were higher than those of southern group; while in southern group, A*3103, 3201 and 6801 were absent, the frequencies of A*0203 and 1101 were higher than those of northern group; and in addition, six subtypes of A2 serological specificity, namely A*0201, 0203, 0205, 0206, 0207 and 0210, were found, in which A*0201 predominated. CONCLUSION: There are some differences in the genetic background of northern and southern Chinese. A2 subtypes have important implications for unrelated-donor transplantation.

Alleles↗
PubMed1999

[Polymorphism of HLA-DRB1, DQB1 in the Hans of north China].

OBJECTIVE: To understand polymorphism of HLA-DRB1, DQB1 in the Hans of north China and obtain more comprehensive and accurate data on genetics at DNA level. METHODS: Polymerase chain reaction-sequence specific primers (PCR-SSP) were used to determine HLA-DRB1, DQB1 alleles in 107 unrelated healthy Han individuals of north China. RESULTS: The authors determined 14 DRB1, 9 DQB1 alleles, which included not only the allele frequencies that corresponded to the gene frequencies of DR, DQ loci determined by other 9 cooperating labs but also the allele frequencies of DRB1*15, DRB1*16, DQB1*0301, DQB1*0302, DQB1*0303, DQB1*05, DQB1*0601, DQB1*0602, and DQB1*0604 that other serology labs did not report. CONCLUSION: This study has obtained a more comprehensive and accurate data set of the normal allele frequencies and linkage disequilibrium parameters of HLA-DRB1, DQB1 in the Hans of north China, which may be of significance in the studies on population genetics and disease association.

Alleles↗
PubMed1999

Effects of tylosin on concentrations of Fusobacterium necrophorum and fermentation products in the rumen of cattle fed a high-concentrate diet.

OBJECTIVE: To determine effects of tylosin on ruminal concentrations of Fusobacterium necrophorum and fermentation products in cattle during rapid adaptation to a high-concentrate diet. ANIMALS: 6 steers fitted with ruminal cannulas. PROCEDURE: Steers were assigned randomly to 2 treatment groups and switched from a 0 to an 85% concentrate diet during a 4-day period. Cattle received this diet, with or without tylosin (90 mg/steer/d), for 4 weeks. Samples of ruminal contents were collected daily beginning 2 days before the treatment protocol and in the first week of concentrate feeding. Four subsequent samples were collected at weekly intervals. Concentration of F. necrophorum in samples was determined, using the most-probable-number technique. Ruminal pH and concentrations of volatile fatty acids (VFA), lactate, and ammonia also were determined. All steers received both treatments separated by 4 weeks (cross-over design), during which time they were fed alfalfa hay only. RESULTS: In control steers, concentration of F. necrophorum increased in response to the high-concentrate diet. Tylosin-fed steers had lower concentrations of F. necrophorum than control steers at all times during concentrate feeding. However, ruminal pH and concentrations of lactate, VFA, and ammonia did not differ between treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Tylosin caused a significant reduction in ruminal concentrations of F. necrophorum during rapid adaptation to a high-concentrate diet but had no effect on fermentation products. The reduction in ruminal concentration of F. necrophorum helps explain the reduction in prevalence of hepatic abscesses reported in tylosin-fed feedlot cattle.

Ammonia↗