A exigência em vitaminas do complexo B pode modificar para frangos de corte criados sob condições comerciais (i.e. condições de estresse, presença de doenças, ambiente desfavorável). Esse incremento nos níveis de suplementação vitamínica pode ser necessário para que as aves atinjam elevadas taxas de crescimento, melhorem o aproveitamento dos alimentos e a saúde animal. No presente estudo foram realizados três experimentos com o objetivo de avaliar níveis supranutricionais de suplementação das vitaminas riboflavina, ácido pantotênico, niacina, ácido fólico e vitamina B12 na produção de frangos de corte. Para isto, dois experimentos foram conduzidos em gaiolas para avaliar o efeito dos níveis das vitaminas riboflavina, ácido pantotênico, niacina, ácido fólico e vitamina B12 (controle, três ou seis vezes o controle) e o nível nutricional e energético (regular ou superior) que promoveram as melhores respostas para frangos de corte, sendo no experimento I utilizada dieta vegetal e no experimento II foram incluídas farinhas de origem animal e óleo de soja oxidados na ração. Frangos alimentados com dieta vegetal formulada com densidade nutricional regular apresentaram respostas positivas de ganho de peso (741,1 g vs. 697,3 g) e consumo de ração (920.2 vs. 878.5 g) em relação aos demais tratamentos quando utilizado nível supranutricional seis vezes o controle das vitaminas avaliadas. Por outro lado, os níveis supranutricionais de vitaminas não apresentaram efeitos no desempenho de animais alimentados com ingredientes origem animal e óleo de soja oxidados. Com base nas respostas obtidas nestes experimentos, foram definidos os tratamentos do estudo em aviário experimental, simulando condições comerciais de criação. Utilizou-se dieta vegetal formulada com nível nutricional e energético regular para avaliar o uso de nível de suplementação vitamínica controle e seis vezes o controle em duas condições de estresse, baixa e moderada. Para compor estas condições de estresse foi considerada a combinação de dois fatores: densidade de alojamento (10 aves/m2 ou 11,5 aves/m2) e desafio com vacina contra coccidiose. Aos sete dias de idade, aves sob condição moderada de estresse foram desafiadas com uma dosagem 10 vezes em relação ao recomendado pelo fornecedor de uma vacina contra coccidiose. Após o desafio com a vacina, aves sob moderada condição de estresse apresentaram decréscimo no desempenho em relação as criadas sob baixa condição de estresse. Não houve efeito estatístico do uso de nível supranutricional de vitaminas sobre o desempenho das aves. No entanto, aves alimentadas com superdose de vitaminas seis vezes o controle obtiveram maior rendimento de carcaça em comparação às alimentadas com nível controle (73.16 vs. 72.77%, P = 0.008). Devido ao fato das condições de estresse impostas neste estudo não serem severas como as encontradas no campo, a utilização de nível supranutricional de vitaminas não foi eficiente em recuperar o desempenho das aves. Por outro lado, há um potencial de melhora no rendimento de carcaça com o uso desses níveis. / Vitamin requirements for chickens may increase in adverse conditions, such as stress, diseases, and poor environment. Increased dietary supplementation may be needed for broilers to reach higher growth levels, improve their feed absorption and welfare. Therefore, in the present study, a series of three experiments were designed to evaluate the effect supra-nutritional levels of the vitamins riboflavin, pantothenic acid, niacin, folic acid and vitamin B12 on broiler production. Two experiments were conducted in batteries to assess the supra-nutritional levels of the vitamins mentioned above (control, three- or six-times control), and the dietary nutrient density (low- or high-level) on chickens\' performance. The basal feed differed between experiments: Exp. I - corn and soybean meal-based diet; Exp. II - diet containing oxidized animal by-products and soybean oil. In Exp. I, birds showed greater weight gain (741.1 g vs. 697.3 g) and feed intake (920.2 vs. 878.5 g) when low-density diets with supra-nutritional level six-times control were fed. Nevertheless, there was no effect of supra-nutritional level of the selected B vitamins on performance of chickens in Exp. II. It was therefore decided to study the effects of supra-nutritional levels of the selected B vitamin (control or six- times control) on performance, uniformity, and carcass traits of chickens raised in floor pens under two environmental stress levels (low or moderate). Stocking density (10 birds/m2 or 11.5 birds/m2) and the challenge with coccidiosis vaccine (without or with vaccination) were used as stress agents. At 7d, chicks raised under the moderate condition of stress was challenged with a dosage 10-times higher than the supplier\'s recommendation of a coccidiosis vaccine. The coccidiosis infection impaired the performance of chickens after the challenge. Supra-nutritional level of the B vitamin had no effect on broiler performance. However, the carcass yield was higher when chickens fed super-dose of vitamins six-times control compared to the control treatments (73.16 vs. 72.77%, P = 0.008). Conditions of stress in this study were not severe as in the field and because of this the use of supra-nutritional vitamins had no effect on recovering of chicken performance. Nonetheless, there was a potential improvement in the carcass yield with the use of these levels.

Streptococcus agalactiae is a pathogen of multiple hosts. The bacterium, an aetiological agent of septicaemia and meningo-encephalitis in freshwater and saltwater fish species, is considered a major threat to the aquaculture industry, particularly for tilapia. Cattle and humans are however the main known reservoirs for S. agalactiae. In humans, the bacterium (commonly referred to as Group B Streptococcus or GBS) is a member of the commensal microflora of the intestinal and genito-urinary tracts, but it is also a major cause of neonatal invasive disease and an emerging pathogen in adults. In cattle, S. agalactiae is a well-recognized causative agent of mastitis. Numerous studies focusing on S. agalactiae from human and bovine origins have provided insight into the population structure of the bacterium, as well as the genome content and pathogenic mechanisms through identification of virulence determinants. Concerning S. agalactiae from aquatic origins, scientific information mainly focused on case reporting and/or experimental challenges, with a limited or absence of information in terms of pathogenesis, virulence determinants and genotypes of the strains involved. The objective of this study was to enhance our understanding of the molecular epidemiology, host-adaptation and pathogenicity of S. agalactiae in aquatic species, with particular emphasis on tilapia. Firstly, a collection of 33 piscine, amphibian and sea mammal isolates originating from several countries and continents was assembled, with the aim of exploring the population structure and potential host specificity of aquatic S. agalactiae. Isolates were characterised using pulsed-field gel electrophoresis (PFGE), multi-locus sequence typing (MLST), and a standardised 3-set genotyping system comprising molecular serotypes, surface protein gene profiles and mobile genetic element profiles. Two major subpopulations were identified in fish. The first subpopulation consisted of non-haemolytic isolates that belonged to sequence type (ST) 260 or 261, which are STs that have been reported only from teleosts. These isolates exhibited a low level of genetic diversity by PFGE and clustered with other STs that have been reported only in fish. Another common feature was the absence of all surface protein genes or mobile genetic elements targeted as part of the 3-set genotyping and that are usually found in human or bovine isolates. The second subpopulation consisted of β-haemolytic isolates recovered from fish, frogs and sea mammals, and that exhibited medium to high genetic diversity by PFGE. STs identified among these isolates have previously been identified from strains associated with asymptomatic carriage and invasive disease in humans. The human pathogenic strain ST7 serotype Ia was detected in fish from Asia. Moreover, ST283 serotype III-4 and its novel single locus variant ST491 detected in fish from Southeast Asia shared a 3-set genotype identical to that of an emerging ST283 clone associated with invasive disease of adult humans in Asia. These observations suggested that some strains of aquatic S. agalactiae may present a zoonotic or anthroponotic hazard. STs found among the seal isolates (ST23) have also been reported from humans and numerous other host species, but never from teleosts. This work provided an excellent basis for exploration of the virulence of selected strains in experimental challenges. The virulence of two strains of S. agalactiae was experimentally investigated by intra-peritoneal infection of Nile tilapia (Oreochromis niloticus), using an isolate originally recovered from fish and belonging to ST260, and an isolate originating from a grey seal and belonging to ST23. The clinical signs, the in vivo distribution of viable bacteria and bacterial antigens, and the gross and histopathological lesions that developed during the time course of the infection were investigated. The ST260 strain was highly virulent, whereas no major clinical sign or mortalities occurred in the fish challenged with the ST23 strain. After injection, both strains however gained access to the bloodstream and viable bacteria were recovered from all organs under investigation. During the early stages of infection, bacteria were mostly found within the reticulo-endothelial system of the spleen and kidney. Thereafter, the ST260 demonstrated a particular tropism for the brain and the heart, but granulomatous inflammation and associated necrotic lesions were observed in all organs. ST23 was responsible for a mixed inflammatory response associated with the presence of bacteria in the choroid rete and in the pancreatic tissue only. After 7 days post-challenge and for both strain, the formation or containment of bacteria within granulomata or other encapsulated structures appeared to be a major component of the fish response. However, the load of viable bacteria remained high within organs of fish infected with ST260, suggesting that, unlike ST23, this strain is able to survive within macrophages and/or to evade the immune system of the fish. This work demonstrates that the lack of report of ST23 strains in fish is possibly not due to a lack of exposure but to a lack of virulence in this host. The two strains, which differ in prevalence and virulence in fish, provide an excellent basis to investigate genomic differences underlying the host-association of distinct S. agalactiae subpopulations. The genome of the ST260 strain used in challenge studies was sequenced. We therefore provided the first description for the genome sequence of a non-haemolytic S. agalactiae isolated from tilapia (strain STIR-CD-17) and that belongs by multi-locus sequence typing (MLST) to clonal complex (CC) 552, which corresponds to a presumptive fish-adapted subgroup of S. agalactiae. The genome was compared to 13 S. agalactiae genomes of human (n=7), bovine (n=2), fish (n=3) and unknown (n=1) origins. Phylogenetic analysis based on the core genome identified isolates of CC552 as the most diverged of all S. agalactiae studied. Conversely, genomes from β-haemolytic isolates of CC7 recovered from fish were found to cluster with human isolates of CC7, further supporting the possibility that some strains may represent a zoonotic or anthroponotic hazard. Comparative analysis of the accessory genome enabled the identification of a cluster of genes uniquely shared between CC7 and CC552, which encode proteins that may provide enhanced fitness in specific niches. Other genes identified were specific to STIR-CD-17 or to CC552 based on genomic comparisons; however the extension of this analysis through the PCR screening of a larger population of S. agalactiae suggested that some of these genes may occasionally be present in isolates belonging to CC7. Some of these genes, occurring in clusters, exhibited typical signatures of mobile genetic elements, suggesting their acquisition through horizontal gene transfer. It is not possible to date to determine whether these genes were acquired through intraspecies transfer or through interspecies transfer from the aquatic environment. Finally, general features of STIR-CD-17 highlighted a distinctive genome characterised by an absence of well conserved insertion sequences, an abundance of pseudogenes, a smaller genomic size than normally observed among human or bovine S. agalactiae, and an apparent loss of metabolic functions considered conserved within the bacterial species, indicating that the fish-adapted subgroup of isolates (CC552) has undergone niche restriction. Finally, genes encoding recognised virulence factors in human S. agalactiae were selected and their presence and structural conservation was evaluated within the genome of STIR-CD-17.