Increased understandings of ruminal acidosis in dairy cattle

ABSTRACT Ruminal acidosis remains an important and prevalent disorder of economic and welfare concern to the dairy industry worldwide. There are inconsistencies in the diagnostic techniques and definitions of ruminal acidosis and a requirement for further information on the pathogenesis of ruminal acidosis, in particular in regard to the role of feed substrates, such as starch, sugar, and protein (Chapter 1). A greater understanding of changes to the microbiome during ruminal acidosis, feed management, and the possible synergistic effects of feed additive control agents is also required (Chapter 1). Consequently, the overall hypothesis of this thesis, which was supported, is that starch-, sugar-, and protein- or amino acid-based feed substrates would produce different ruminal and blood measures and distinct rumen bacterial community composition associated with different risks of ruminal acidosis. Secondly, that partial mixed ration feeding strategies and feed additive control agents would promote favorable ruminal conditions and reduce the risk of ruminal acidosis, which was also supported; however, whether feed additive control agents reduced the risk of ruminal acidosis was equivocal. Heifers exposed to a single feeding of grain and fructose had an increased risk of ruminal acidosis and accumulated ruminal lactate, compared to those fed grain only (Chapter 2). This highlights that diets with high sugar content should be fed with caution and increase the risk of ruminal acidosis when physically effective fiber is inadequate. Different oxidative stress responses were not observed among treatment groups of heifers fed single exposures of different substrates (Chapter 3) or different feed additives over a 20 d period (Chapter 7), but were evident in a heifer with acute clinical ruminal acidosis (Chapter 8). This suggests oxidative stress responses may only occur during acute clinical ruminal acidosis. Distinct ruminal bacterial community composition occurred among heifers fed a single exposure to different substrates (Chapter 4) and also among lactating cows fed different feeding strategies at different supplementary feeding amounts (Chapter 5) and these communities were associated with rumen fermentation characteristics. Cattle appeared to have host specific rumen bacteria and a core microbiome (Chapters 4 and 5). This suggests that host specificity in rumen ecosystems may be associated with the individual susceptibilities of cattle to ruminal acidosis and a need to tailor feed management and control for ruminal acidosis for individual cattle. Supplementary feeding amount and ruminal concentrations of propionate and valerate appeared to have the largest association with ruminal bacterial communities in Chapter 5 and may be good predictors of ruminal acidosis. A partial mixed ration feeding system, compared with component feeding, decreased ruminal acidosis (Chapter 5), suggesting benefits of this feeding system; however, milk production and milk component benefits were not observed for this feeding system. Feed additive control agents perturbed the rumen by different mechanisms but had minimal synergistic effects when combinations of feed additives were fed and ruminal acidosis control was equivocal (Chapters 6 and 7). Feed additives may not be capable of controlling ruminal acidosis in all cattle when large amounts of readily fermentable carbohydrates are fed (Chapter 7). Concentrations of the volatile fatty acids (VFA): butyrate, propionate, valerate, isobutyrate, isovalerate, and caproate were below detectable limits in a heifer with acute clinical ruminal acidosis 24 h after she consumed a ration with 19.1% sugar and 54.1% starch on a DM basis and her acetate concentration was <20 mM. However, concentrations of these VFA were higher 55 h after she consumed the ration. These findings demonstrate that the rumen is extremely dynamic and can rapidly recover from severe perturbation. Throughout this thesis it has been evident that classic models of ruminal acidosis may not be sufficient to describe the pathogenesis of ruminal acidosis when diets with a high sugar content are fed and uncharacterized rumen bacteria may be involved in the pathogenesis of ruminal acidosis. Definitions of ruminal acidosis to describe acidosis when cattle are fed different substrates, in particular diets with a high sugar content are required. The rumen appears to be better adapted to respond to changes in starch intakes, compared with sugar intakes and cattle have individual rumen responses and susceptibilities to ruminal acidosis during shifts in feed substrates. In summary, this thesis has increased our understandings of the pathogenesis of ruminal acidosis and control strategies for ruminal acidosis in cattle

The Middle Jurassic dinoflagellate cyst biostratigraphy of the Lusitanian Basin, Portugal [Resumo]

ABSTRACT: A mainly Middle Jurassic composite succession with 129 samples was examined palynologically. This spans the Toarcian–Aalenian transition to the lowermost Bathonian, exposed at Cabo Mondego (includes the GSSP and the ASSP for the Bajocian and Bathonian stages respectively) and São Gião in the northern Lusitanian Basin, western Portugal. The main goal was to establish a biostratigraphical scheme based on dinoflagellate cysts bioevents.N/

Full restoration of viral fitness by multiple compensatory co-mutations in the nucleoprotein of influenza A virus cytotoxic T-lymphocyte escape mutants

Amino acid substitutions have been identified in the influenza A virus nucleoprotein that are associated with escape from recognition by virus-specific cytotoxic T lymphocytes (CTLs). One of these is the arginine-to-glycine substitution at position 384 (R384G). This substitution alone, however, is detrimental to viral fitness, which is overcome in part by the functionally compensating co-mutation E375G. Here, the effect on viral fitness of four other co-mutations associated with R384G was investigated by using plasmid-driven rescue of mutant viruses. Whilst none of these alternative co-mutations alone compensated functionally for the detrimental effect of the R384G substitution, the M239V substitution improved viral fitness of viruses containing 375G and 384R. The nucleoprotein displays unexpected flexibility to overcome functional constraints imposed by CTL epitope sequences, allowing influenza viruses to escape from specific CTLs

Scheme for the implementation of a universal quantum cloning machine via cavity-assisted atomic collisions in cavity QED

We propose a scheme to implement the $1\to2$ universal quantum cloning machine of Buzek et.al [Phys. Rev.A 54, 1844(1996)] in the context of cavity QED. The scheme requires cavity-assisted collision processes between atoms, which cross through nonresonant cavity fields in the vacuum states. The cavity fields are only virtually excited to face the decoherence problem. That's why the requirements on the cavity quality factor can be loosened.Comment: to appear in PR

Fast linear algebra is stable

In an earlier paper, we showed that a large class of fast recursive matrix multiplication algorithms is stable in a normwise sense, and that in fact if multiplication of $n$-by-$n$ matrices can be done by any algorithm in $O(n^{\omega + \eta})$ operations for any $\eta > 0$, then it can be done stably in $O(n^{\omega + \eta})$ operations for any $\eta > 0$. Here we extend this result to show that essentially all standard linear algebra operations, including LU decomposition, QR decomposition, linear equation solving, matrix inversion, solving least squares problems, (generalized) eigenvalue problems and the singular value decomposition can also be done stably (in a normwise sense) in $O(n^{\omega + \eta})$ operations.Comment: 26 pages; final version; to appear in Numerische Mathemati

Passive transfer and rate of decay of maternal antibody against African horse sickness virus in South African throughbred foals

REASONS FOR PERFORMING STUDY : African horse sickness is an insect transmitted, non-contagious disease of equids caused by African horse sickness virus (AHSV). Mortality can exceed 90% in fully susceptible horse populations. A live-attenuated (modified-live) cell culture-adapted (MLV) polyvalent AHSV vaccine is widely used to control AHS in endemic areas in southern Africa. Field studies detailing antibody responses of vaccinated horses are lacking. OBJECTIVES : To determine antibody titres to the 9 known serotypes of AHSV in a cohort of brood mares that were regularly vaccinated with the MLV AHSV vaccine, and to measure the passive transfer and rate of decay of maternal antibody to the individual virus serotypes in foals. METHODS : Serum was collected from 15 mares before foaling and from their foals after foaling and monthly thereafter for 6 months. Antibody titres to each of the 9 AHSV serotypes were determined by serum-virus neutralisation assay. RESULTS : There was marked variation in the antibody response of the mares to individual AHSV serotypes even after repeated vaccination, with consistently higher titre responses to some virus serotypes. Similarly, duration of maternally-derived antibodies in foals differed among serotypes. CONCLUSIONS : Data from this study confirm variation of the neutralising antibody response of individual mares to repeated vaccination with polyvalent AHSV vaccine. Virus strains of individual AHSV serotypes included in the vaccine may vary in their inherent immunogenicity. Passivelyacquired maternal antibodies to AHSV vary markedly among foals born to vaccinated mares, with further variation in the duration of passive immunity to individual AHSV serotypes. POTENTIAL RELEVANCE : These data are relevant to the effective utilization of live-attenuated AHSV vaccines in endemic regions, and potentially to the use of vaccines in response to future incursions of AHSV into previously free regions. Further studies involving a larger population will be required to determine the optimal time for vaccinating foals.Racing South Africa and the Equine Research Centre, University of Pretoria.http://www.evj.co.uk/journals/hb2013ab201