Logo Locus

Communities in DSpace

Select a community to browse its collections.

Now showing 1 - 6 of 6

Recent Submissions

  • Thumbnail Image
    Item type:Item,
    Three studies on ruminant nutrition
    (Universidade Federal de Viçosa, 2026-03-05) Sousa, Luiz Carlos Oliveira de; Detmann, Edenio; http://lattes.cnpq.br/3143335212298569
    This thesis comprised three independent experiments on ruminant nutrition. In the first experiment, our objective was to evaluate whether guanidinoacetic acid (GAA) affects the performance, metabolism, and placental vascularization in pregnant beef cows during late gestation as well as its impact on the offspring’s performance. Twenty-eight pregnant Brahman cows (body weight = 532±15.1 kg) carrying male (n=15) and female (n=13) fetuses, were used. On day 170 of gestation, cows were housed in individual pens and fed a corn silage-based diet. Two treatments were evaluated: 1) control (no addition of GAA) or 2) addition of 0.2% GAA to the total diet (on a dry matter basis). Maternal treatments started on day 180 and extended until day 270 of gestation. Our results showed that providing GAA decreased skeletal muscle mobilization and enhanced placental vascularization in beef cows during late gestation. However, we did not observe any impact of GAA on performance of the offspring. Notably, dietary GAA addition induced a deficiency of methyl groups, leading to decreased plasma methionine. In the second experiment, we investigated methodological variations in in vitro gas production techniques. Our objective was to evaluate the influence of substrate dispersion method and particle size on in vitro digestibility, gas production kinetics and composition, and fermentation characteristics of different feed types. Alfalfa hay, tall fescue hay, ground corn, soybean meal, and a total mixed ration (TMR) were used as substrates. Treatments were designed according to a 2 × 2 × 5 factorial arrangement, consisting of two substrate dispersion methods (loose substrate and in filter bags), two particle sizes (1 mm and 2 mm), and five feeds. The experiment was conducted over four incubations, with two bottles per treatment in each incubation. Cumulative gas pressure was recorded at 5-minute intervals throughout a 72-h incubation period. Our findings showed that incubating substrates in filter bags compromised in vitro digestibility, gas production, and fermentation characteristics regardless of particle size. However, the magnitude of responses was greater for forage-based feeds than concentrate feeds. In the third experiment, we aimed to investigate the effects of soybean-based feeds on feeding behavior, arterial hemodynamics, heat stress responses, and metabolic and inflammatory indicators in beef cattle experiencing fescue toxicosis. Ten ruminally-cannulated Angus × Holstein steers were used in a 5 × 10 Latin rectangle design. Five treatments were evaluated: 1) non-toxic endophyte-infected tall fescue seed (NTE), 2) toxic endophyte-infected tall fescue seed (TE), 3) TE + soybean hulls (SBH), 4) TE + whole soybean (WSB), or 5) TE + soybean meal (SBM). Treatment periods lasted 7 d, followed by a 14-d washout. Soybean meal supplementation mitigated ergot alkaloid-induced vasoconstriction, promoted vasodilation, and restored normal feeding behavior in beef cattle experiencing fescue toxicosis. Additionally, soybean meal supplementation increased peripheral serotonin concentration, which may be associated with the beneficial physiological responses observed in beef cattle during fescue toxicosis. Keywords: cattle; metabolism; in vitro.
  • Thumbnail Image
    Item type:Item,
    Effects of nutritional strategies on metabolic and productive responses in Nellore heifers under grazing
    (Universidade Federal de Viçosa, 2026-03-08) Pistillo, Letícia Zamberlan; Sampaio, Claudia Batista; http://lattes.cnpq.br/6262691394515838
    This thesis investigated the effects of different nutritional strategies during the rearing period on growth performance, metabolic responses, and developmental parameters of grazing Nellore heifers. Nutritional management during the post-weaning and prepubertal phases is essential to ensure adequate growth before the reproductive period, particularly in tropical grazing systems, where animal performance is strongly influenced by forage availability and seasonal variation in forage quality. Thus, two studies were conducted to evaluate supplementation strategies aimed at supporting growth efficiency. The first study evaluated a stair-step supplementation strategy (SST), comparing continuous gain (CONG) with compensatory gain (COMPG). Forty nulliparous heifers were assigned to CONG, receiving 5 g/kg of concentrate supplement for 120 days, or COMPG, receiving 2 g/kg for 60 days followed by 8 g/kg for 60 days. A treatment × day interaction was observed for BW and ADG (p < 0.001). CONG showed greater performance during the initial phase, but COMPG reached similar final BW by the end of the experiment. BCS, body measurements, and fat thicknesses were mainly affected by day (p < 0.001), whereas ribeye area showed a treatment × day interaction (p < 0.005). Metabolic responses showed treatment × day interactions for total protein, IGF-1, and SUN (p < 0.036, p < 0.001, and p < 0.001, respectively). These results indicate that SST promoted compensatory growth without impairing final development. The second study evaluated yeast supplementation during the prepubertal phase. Thirty-six nulliparous heifers were assigned to concentrate supplements containing yeast cell wall product (YCW), or live yeast, either Saccharomyces cerevisiae (SC) or Saccharomyces boulardii (SB). A treatment × day interaction was observed for BW (p = 0.018), with SB tending to show greater final BW than SC, whereas YCW was intermediate. ADG increased over time (p = 0.016), but no consistent treatment effect was observed. No treatment effects were detected for ribeye area (p > 0.05), whereas subcutaneous fat increased over time (p < 0.001). Glucose and SUN increased (P = 0.024 and p = 0.043), while IGF-1 decreased (p = 0.046) over time. Reproductive variables were not affected by treatments (p > 0.05). Overall, yeast-based additives had limited effects on performance, metabolic responses, and reproductive parameters under grazing conditions. Collectively, these findings show that nutritional strategies can be used during the rearing phase of Nellore heifers without compromising growth and development. Keywords: Bos indicus; compensatory gain; prepubertal development; tropical grazing systems; yeast supplementation.
  • Thumbnail Image
    Item type:Item,
    Integrated approaches to dairy cow performance: nutrition, reproduction, and production systems
    (Universidade Federal de Viçosa, 2026-02-27) Oliveira, Kellen Ribeiro de; Rotta, Polyana Pizzi; http://lattes.cnpq.br/8192716170118709
    Dairy cow performance in tropical production systems results from complex interactions among nutritional efficiency, postpartum health, reproductive management, and housing environment. Advancing sustainable dairy production therefore requires an integrated understanding of how these biological and management components influence productivity, resilience, and environmental outcomes. This thesis investigated key determinants of dairy system performance through four complementary studies combining controlled experimentation, large- scale retrospective analyses, and on-farm environmental assessment. The first study evaluated supplementation with the live yeast Saccharomyces cerevisiae CNCM I- 1077 and demonstrated improvements in rumen degradability of fibrous feeds, enhanced nutrient utilization, and greater feed efficiency. These findings indicate that optimizing rumen kinetics can improve metabolic efficiency and help mitigate environmental stress without necessarily altering microbial diversity. The second study analyzed retained placenta in commercial dairy herds under tropical conditions using a large retrospective dataset. Retained placenta was associated with cows’ breed, parity, and calving characteristics, and consistently resulted in reduced pregnancy per insemination, increased pregnancy loss, and greater risk of culling. These results confirm that postpartum disorders exert persistent effects on reproductive outcomes and herd longevity, highlighting the importance of preventive health strategies. The third study examined herd-level reproductive performance and showed that management intensity and housing system are major determinants of reproductive efficiency. More frequent reproductive monitoring was primarily associated with improved service rate and shorter intervals between inseminations, whereas compost barn and free stall systems had superior reproductive outcomes compared with dry lot systems. These findings emphasize that reproductive success in commercial herds is strongly related to management rather than fertility itself. The fourth study evaluated manure excretion dynamics in compost barn systems and demonstrated that the concentration of feces and urine within the bedding promotes composting and substantially reduces nitrogen requiring external treatment. This redistribution of nutrient flows enhances recycling efficiency and illustrates how housing design can simultaneously support environmental sustainability and animal welfare. Together, these studies demonstrate that improving dairy production in tropical environments requires a system-level approach integrating digestive efficiency, postpartum health, reproductive management, and production system design. Collectively, these findings highlight how nutrition, reproduction, management, and production system design shape productivity and sustainability in modern dairy systems. Keywords: dairy systems; herd management; reproductive efficiency; rumen function; sustainability; tropical production.
  • Thumbnail Image
    Item type:Item,
    Previsão da dinâmica sazonal de Frankliniella schultzei (Thysanoptera: Thripidae) em cultivos de tabaco usando redes neurais artificiais
    (Universidade Federal de Viçosa, 2026-06-25) Donato, Conceição Aparecida da Silva; Picanço, Marcelo Coutinho
    Os cultivos de tabaco (Nicotiana tabacum) têm grande importância econômica e social devido a renda e aos empregos gerados. O tripes Frankliniella schultzei (Thysanoptera, Thripidae) é uma das principais pragas nesses cultivos. A compreensão da dinâmica populacional das pragas é importante para os programas de Manejo Integrado de Pragas, pois isso possibilita se identificar os fatores reguladores e prever períodos de maior ocorrência desses organismos. As Redes Neurais Artificiais (RNAs) destacam-se como ferramentas de inteligência artificial com elevado potencial para modelar e prever fenômenos complexos, como a dinâmica sazonal de populações de pragas. Assim, esse trabalho teve como objetivo determinar um modelo de previsão da dinâmica sazonal de F. schultzei em cultivos de tabaco usando RNAs. Para tanto, durante três anos em 87 cultivos conduzidos em pivôs centrais de cerca de 150 ha foram monitoradas a cada cinco dias as densidades de F. schultzei, a idade das plantas de tabaco e os elementos climáticos. Foram determinadas 1320 RNAs e foi selecionada aquela com maior poder preditivo. Essa RNA foi validada e posteriormente, o seu desempenho foi comparado com modelos de Floresta aleatória, regressão linear múltipla e ARIMA. A RNA selecionada utilizou como preditores a idade das plantas de tabaco, a temperatura média do ar, a velocidade média dos ventos e a precipitação pluviométrica. Nesse modelo foi usada uma defasagem de 30 dias para os elementos climáticos e ele possui dez neurônios na camada oculta, função de ativação tangente hiperbólica e algoritmo de aprendizado resiliente backpropagation. Essa RNA apresentou o melhor desempenho preditivo entre as RNAs avaliadas e do que os modelos de Floresta Aleatória, Regressão Linear Múltipla e ARIMA. Verificou-se que o aumento da densidade populacional desse tripes nos cultivos de tabaco esteve associado ao aumento da idade das plantas e com períodos de temperaturas mais amenas, precipitação pluviométrica intermediária e menores velocidades dos ventos. Portanto, o modelo de RNA estabelecido neste trabalho é apropriado para determinar a dinâmica sazonal de F. schultzei nos cultivos de tabaco. Palavras-chave: Nicotiana tabacum; Tripes; Inteligência artificial; Elementos climáticos; Idade das plantas
  • Thumbnail Image
    Item type:Item,
    Avaliação da compatibilidade entre produto comercial biológico à base de Bacillus velezensis e defensivos químicos in vitro
    (Universidade Federal de Viçosa, 2025-09-25) Gomes, Karolline de Paula Silva; Machado, Franklin Jackson; http://lattes.cnpq.br/1277255558797637
    O uso de agentes biológicos, como Bacillus velezensis, tem se destacado no manejo integrado de doenças, sendo uma alternativa sustentável aos defensivos químicos. No entanto, a compatibilidade físico-química e biológica entre biofungicidas e agroquímicos é essencial para garantir a eficácia da aplicação em tanque. Este estudo avaliou, in vitro, (i) a compatibilidade de um produto comercial biológico à base de B. velezensis com diferentes grupos de defensivos químicos, determinando o impacto dessas misturas no crescimento e na viabilidade do microrganismo após duas horas de exposição, (ii) as propriedades físico-químicas das caldas, visando identificar possíveis alterações que pudessem comprometer sua estabilidade e eficácia em condições de laboratório. Três experimentos foram conduzidos: (i) determinação da diluição ideal do biofungicida para contagem de unidades formadoras de colônia (UFC), (ii) avaliação da viabilidade microbiana após duas horas de exposição às misturas e (iii) análise quantitativa (pH, condutividade elétrica e temperatura) e qualitativa (flotação, sedimentação, formação de grumos e separação de fases) das caldas. Os resultados indicaram que a maioria das misturas manteve condições adequadas para a sobrevivência do agente de controle biológico, porém, algumas combinações, especialmente aquelas contendo glifosato, mancozebe, clorotalonil e acefato, apresentaram alterações significativas no crescimento de Bacillus velezensis, pH, condutividade elétrica e características visuais, como formação de grumos, sedimentação e separação de fases, sugerindo incompatibilidade. Estes achados evidenciam que a interação entre princípios ativos pode influenciar a compatibilidade biológica e físico-química, reforçando a importância de avaliações prévias de misturas para otimizar a eficácia do biofungicida e promover a sustentabilidade do manejo fitossanitário. Palavras-chave: misturas de agroquímicos; compatibilidade físico-química; eficiência biológica; manejo integrado de doenças