Commercial equipment used by the turkey industry at hatch sterilizes the germinal tissue of the claw with microwave energy and the beak tissue with infrared energy. This effectively claw and beak trims the birds. To test this technique on chickens, one-half of two strains of 1,200 Leghorn chicks were each subjected to the claw reduction (RC) technique at hatch, while one-half retained intact claws (IC). The beaks of one-third of these treatments were reduced at hatch using the infrared technique (1-day), one-third were precision trimmed at 7 d of age (7-day), and one-third were not trimmed (IB). Body weight, weight gain, feed intake, feed conversion, mortality, and fearfulness were measured. Rearing followed standard commercial feeding and husbandry procedures. During the preliminary experiment, heterophil to lymphocyte ratios did not consistently differ significantly between treatments. The RC birds had significantly lower body weight, except from 3 to 6 wk and had significantly lower feed consumption from 8 to 18 wk. The 1-day beak trimmed (BT) birds had significantly lower body weight from 3 to 14 wk and ate less total feed by 4 wk. Subjective evaluation showed that the RC birds exhibited less fearfulness during the growing period than the IC birds. Throughout lay, the body weight of RC and BT birds was significantly affected. Feed consumption was not lessened for RC birds, but was for BT birds throughout lay. Egg production, egg quality, and mortality were not affected by either treatment. / Master of Science

none

Die subklinische Klauenrehe oder claw horn disruption (CHD) ist von großer wirtschaftlicher Bedeutung für die Rinderhaltung, da sie zu Lahmheiten, Beeinträchtigungen des Allgemeinbefindens sowie einer eingeschränkten Leistungsfähigkeit der Tiere führt. Trotz zahlreicher Untersuchungen sind die pathophysiologischen Grundlagen der CHD noch immer nicht vollständig geklärt. Die derzeitigen Hypothesen weisen auf eine Ischämie in den noch lebensfähigen Epidermisschichten infolge einer veränderten dermalen Mikrozirkulation. Diese hat pathophysiologische Veränderungen zur Folge, die eine Störung der epidermalen Zellproliferation, eine Schädigung der dermo-epidermalen Verbindung sowie eine veränderte Keratinisierung und Hornproduktion umfassen. Von Bedeutung sind daher In-vitro-Ischämiemodelle, um die epidermale Reaktionsmechanismen auf die pathologischen Veränderungen der Dermis zu untersuchen. Ziel in der vorliegenden Arbeit war die Etablierung eines In-vitro-Ischämiemodells auf der Grundlage boviner Keratinozyten aus der Klauenepidermis. Mithilfe dieses Modells sollten die zellulären Pathomechanismen infolge einer Ischämie, einer Hypoxie sowie eines Glukoseentzugs untersucht werden. Des Weiteren stand die Analyse des Differenzierungsverhaltens der Keratinozyten infolge ischämischer, hypoxischer und hypoglykämischer Konditionen im Mittelpunkt. Für die Etablierung des In-vitro-Ischämiemodells diente als Grundlage das oxygen glucose deprivation (OGD)-Modell, das die Untersuchung eines gleichzeitigen Sauerstoff- und Glukosemangels sowie lediglich einer Hypoxie und eines Glukoseentzugs bei bovinen Keratinozyten ermöglichte. Die Versuche wurden in eine Kurzzeitanalyse über 96 Stunden sowie eine Langzeitanalyse über drei Wochen geteilt. Nach erfolgter Exposition wurde die Zellviabilität mittels LDH(Lactatdehydrogenase)- und MTT(3-(4,5-Dimethylhiazol-2-yl)-2,5-diphenyltetrazoliumbromid)-Assay untersucht. Des Weiteren wurde das veränderte Differenzierungsverhalten der Keratinozyten infolge der veränderten Kultivierungsbedingungen mittels Western Blot-Analyse anhand der Involukrin- und Lorikrin-Expression untersucht. Die Keratinozyten zeigten infolge einer OGD nach kurzer Expositionsdauer die höchsten zytotoxischen Effekte, die von einer zeitabhängigen Abnahme der Zellviabilität sowie massiven morphologischen Veränderungen gefolgt wurde. Hypoxische Bedingungen bewirkten eine zeitabhängige Abnahme der Zellviabilität, die erst nach zweiwöchiger Inkubation die größte Zytotoxizität aufwies, sowie eine geringgradig veränderte Zellmorphologie bei Erhaltung des Zellverbands. Der Glukoseentzug bewirkte eine stark verminderte Zellviabilität sowie starke morphologische Zellveränderungen. In der Western Blot-Analyse konnte eine gesteigerte Involukrin- und Lorikrin-Expression infolge einer OGD, einer Hypoxie und eines Glukoseentzugs nachgewiesen werden. In der vorliegenden Arbeit konnte erstmalig ein auf bovinen Keratinozyten basierendes In-vitro-Ischämiemodell etabliert werden, das die Untersuchung zellulärer Mechanismen der Epidermis ermöglichte. Die OGD zeigte den stärksten Einfluss auf die Zellviabilität sowie eine veränderte Zelldifferenzierung der Keratinozyten, was die pathophysiologischen Veränderungen im Rahmen der CHD reflektiert. Die ebenfalls starken Zellveränderungen infolge eines Glukoseentzugs verdeutlichen die Rolle der Glukose im Zellmetabolismus der Keratinozyten. Solch ein epidermaler Glukosemangel ist in Verbindung mit der negativen Energiebilanz der Rinder im peripartalen Zeitraum denkbar. Die Ergebnisse infolge einer Hypoxie verweisen auf vielfältige Adaptationsmechanismen der Keratinozyten an hypoxische Bedingungen, denen sie in der Epidermis in vivo während der Zelldifferenzierung ausgesetzt werden. Damit besitzt das In-vitro-Ischämiemodell ein großes Potenzial für den Einsatz in der Klauenreheforschung, um einerseits die mit einer Ischämie einhergehenden pathologischen Veränderungen der CHD untersuchen zu können. Andererseits liefert das Modell wertvolle Informationen zu den physiologischen Grundlagenmechanismen der Epidermis, die mit der Zelldifferenzierung einhergehen. / The subclinical laminitis or claw horn disruption (CHD) is of great economic importance in the dairy industry as it causes lameness, poor general condition and reduced performance. Despite extensive research efforts, the pathomechanism of CHD remains widely unclear. The current hypotheses on CHD pathogenesis include ischemic alterations of the epidermal keratinocytes resulting from an impaired blood supply. This causes an alteration of cell proliferation, a dermo-epidermal separation and an impaired keratinization and horn production. Therefore, in vitro ischemia models are of critical importance in clarification of the epidermal responses to an altered microcirculation. The aim of this study was the establishment of an in vitro ischemia model based on bovine claw keratinocytes. This in vitro model should enable the investigation of cellular pathomechanisms following exposure to ischemia, hypoxia and glucose deprivation. An additional aim was the analysis of the differentiation pattern of keratinocytes under ischemic, hypoxic and hypoglycaemic conditions. To establish the in vitro ischemia model, the keratinocytes were exposed to oxygen-glucose deprivation (OGD). In addition, this model allowed the parallel examination of hypoxic and hypoglycaemic conditions on bovine claw keratinocytes. The experiments were divided into a short-term analysis over 96h and a long-term analysis over three weeks. Measurement of cell viability was performed by LDH(lactatedehydrogenase) and MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra- zolium bromide) assays. Furthermore, the differentiation pattern of the keratinocytes after exposure to ischemia, hypoxia and glucose deprivation was detected by western blot analysis of the focus on expression of involucrin and loricrin. The highest cytotoxic effect was measured after short exposure to OGD followed by a time-dependent decrease of cell viability and extensive morphological changes of the keratinocytes. Hypoxic conditions lead to a time-dependent decrease of cell viability with the highest cytotoxicity after two weeks. The keratinocytes showed slight changes in cell morphology while maintaining a confluent cell layer. Exposure of keratinocytes to glucose deprivation showed a high decrease of cell viability and strong morphological changes. Furthermore, western blot analysis showed an altered expression pattern with increased involucrin and loricrin levels after exposure to OGD, hypoxia and glucose deprivation. The present study established for the first time an in vitro ischemia model based on bovine claw keratinocytes to study the cellular mechanisms of the epidermis. After exposure to OGD, keratinocytes showed the highest loss in cell viability and an altered cell differentiation. This reflects the pathophysiological changes following epidermal ischemia occurring during the pathogenesis of CHD. The massive cellular alterations after glucose deprivation provide good evidence for the importance of glucose in the cellular metabolism of keratinocytes. An epidermal glucose deficiency may occur in combination with a negative energy balance during peripartal period in cattle. The results of hypoxia show the different adaptive mechanisms of keratinocytes to hypoxic conditions which are present in the epidermis during cell differentiation. Thus, the in vitro ischemia model has a great potential for use in research into CHD pathogenesis and pathomechanisms associated with ischemia. On one side, it is possible to investigate the pathological changes following ischemia during CHD. On the other side, the model offers useful information on physiological response mechanisms of the epidermis that correlate with cell differentiation.

Toe trimming within the turkey industry has been used for over four decades as a method for controlling carcass scratching, and by doing so, achieving better grades and lower condemnation rates. The industry has changed greatly since the 1970’s, when the majority of the research on the procedure was completed. The technology used for toe trimming has switched from a hot-blade to the use of microwave energy, which will effect healing and toe length trimmed. The birds are larger now, which will impact mobility both before and after trimming, and in a consumer-driven trend, the industry is re-examining its codes of practice to ensure the highest level of welfare possible. As there is little pertinent research regarding these changes, the toe trimming procedure was re-examined under modern conditions and with focus on both production and welfare effects to determine if the practice can still be recommended. Hybrid Converter toms were raised to 140 d of age, with half (153) being toe trimmed at the hatchery using a Microwave Claw Processor (MCP) and the other half (153) left with their toes intact. The birds had feed consumption, body weight, mortality, toe length, stance, behaviour, and gait scores monitored throughout the trial with carcass damage assessed at processing. Means were considered significantly different when P≤0.05. Toe trimming caused a reduction in both feed consumption and body weight in the later stages of the experiment. Final weights for non-toe trimmed and toe trimmed toms were 21.70 kgs and 21.15 kgs, respectively. Feed efficiency with and without being corrected for mortality was unaffected by the procedure. Overall mortality and mortality by age group were also unaffected; however it was found that toe trimmed toms experienced higher levels of rotated tibia at 3.27% versus 0.65% for untrimmed birds. Toe length measurements found that trimmed toes were, on average, 91.9% the length of an intact toe, and that variability in length increased with trimming. The procedure was not found to impact stance or gait score, although behaviour at all ages measured demonstrated reduced mobility with trimming. In particular, reduced activity in poults for 5 d post-treatment indicates that the MCP treatment caused pain or discomfort. The percentage of carcasses which exhibited scratching was 15.6% for the non-trimmed treatment and 13.3% for the trimmed, which were not significantly different. Also, no significant effect of trimming was found for any other carcass damage category. Based on the negative impacts of toe trimming on both bird production and welfare found in this research, MCP treatment should not be recommended to turkey producers when raising heavy toms.

The objective of this study was to evaluate the claw characteristics contributing to the shape and balance of the foot in growing steers. The evaluated parameters included dorsal wall growth, abrasion, length and sole surface area. After animal harvest, the sole horn thickness was measured. Seventy-two yearling Angus-crossbred steers (mean body weight 378±6.2 kg) were allotted for the finishing period (133 days) to two systems (feedlot, pasture). The feedlot steers were fed a corn-grain/corn silage diet and were housed in pens with concrete floors. Steers assigned to the pasture were rotationally stocked on mixed grass-legume pastures. The claw measurements were obtained from medial and lateral claws of the left rear foot on days 0, 56 and 133. Sole thickness measurements were performed on both front feet. Data were analyzed with repeated measures analysis of variance using a mixed effects model. The horn growth of the dorsal wall was greater (P<0.01) in the feedlot steers (29.5±0.7 mm/finishing period) compared to the steers on pasture (21.28±0.8 mm/ finishing period). Claw horn abrasion was also greater (P<0.001) in feed lot steers (24.50±0.92 mm/ finishing period) than in steers on pasture (9.3±0.9 mm/ finishing period). Lateral and medial claws grew (P<0.001) and wore (P<0.001) at different rates in feedlot steers. In the pasture steers the lateral and medial claws did not differ in growth or abrasion. The change in length of the dorsal wall was different (P<0.05) between feedlot and pasture steers. The difference between lateral and medial claw was significant only in the feedlot steers (P<0.001). The final dorsal wall length, as a result of horn growth and abrasion, was different (P<0.05) between finishing systems. Lateral and medial claw (P<0.001) was different in the feedlot steers only. The change in the sole surface area was different (P<0.05) between feedlot and pasture steers and between lateral and medial claw in both finishing systems. In both finishing systems, medial claws exhibited a smaller surface area than lateral claws. The feedlot steers had significantly thicker soles in all locations than steers on pasture. The steers in confinement on concrete floors, fed a corn-grain/corn silage diet exhibited faster horn growth and abrasion rates, yet smaller sole surface area, shorter dorsal walls and thicker sole horn compared to the steers grazing pasture. The difference between lateral and medial claws for all measured parameters, except sole thickness, was significant in the feedlot steers. / Master of Science

Baigiamasis darbas išdėstytas 42 puslapiuose. Literatūros sąrašą sudaro 43 literatūros šaltiniai.Tyrimas atliktas 2011–2013 metais trijų rajonų – Kauno, Marijampolės ir Telšių skirtingo ūkininkavimo tipo, įvairaus dydžio, pienininkyste besiverčiančiuose ūkiuose.Ištyrėme 37 karves, kurių 30 sirgo nagų ligomis, o 7 karvių nagos buvo patikrintos profilaktiškai. Nustatėme, jog tiriamuoju laikotarpiu karvės dažniausiai sirgo neužkrečiamos kilmės nagų ligomis: aseptiniu pododermatitu, pado opa, laminitu. Dažniausia šių ligų lokalizacija – galinių kojų nagos. / Work size is 42 pages.The list of references includes 43 sources.The study was conducted in 2011–2013 in the three districts - Kaunas, Marijampolė and Telšiai, different sized dairy farms using a different type of farming system.: We have examined 37 cows, 30 of which had claw diseases and 7 cows was tested prophylactically against claw diseases. We found that during the entire period the cows mostly had claw disorders of non-infectious origin: aseptic pododermatitis, sole ulcers, laminitis. The most common location of the diseases were hindlimb claws.

Jackson and Wormald show that every 3-connected K_1,d-free graph, on n vertices, contains a cycle of length at least 1/2 n^g(d) where g(d) = (log_2 6 + 2 log_2 (2d+1))^-1. For d = 3, g(d) ~ 0.122. Improving this bound, we prove that if G is a 3-connected claw-free graph on at least 6 vertices, then there exists a cycle C in G such that |E(C)| is at least c n^g+5, where g = log_3 2 and c > 1/7 is a constant. To do this, we instead prove a stronger theorem that requires the cycle to contain two specified edges. We then use Tutte decomposition to partition the graph and then use the inductive hypothesis of our theorem to find paths or cycles in the different parts of the decomposition.

Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-09-09T12:52:18Z No. of bitstreams: 1 Nei Freitas Nunes Neto.pdf: 1548297 bytes, checksum: d2a73a187d3959051872d9f5a0509926 (MD5) / Approved for entry into archive by Fatima Cleômenis Botelho Maria (botelho@ufba.br) on 2014-09-09T13:08:16Z (GMT) No. of bitstreams: 1 Nei Freitas Nunes Neto.pdf: 1548297 bytes, checksum: d2a73a187d3959051872d9f5a0509926 (MD5) / Made available in DSpace on 2014-09-09T13:08:16Z (GMT). No. of bitstreams: 1 Nei Freitas Nunes Neto.pdf: 1548297 bytes, checksum: d2a73a187d3959051872d9f5a0509926 (MD5) / Gaia é um programa de pesquisa científico, que foi proposto pelo químico inglês James Lovelock, no final da década de 1960, a partir de estudos desenvolvidos por ele para a NASA, com o objetivo de formular métodos para a detecção de vida em outros planetas. O programa de pesquisa foi fortemente rejeitado pela comunidade científica nos primeiros anos de sua história, ao passo que foi recebido com entusiasmo por grupos espiritualistas e ambientalistas. Entretanto, a rejeição da comunidade científica tem sido significativamente reduzida, sobretudo a partir de meados dos anos 1980 e anos 1990. Neste trabalho, temos como objetivo oferecer uma abordagem consistente para as atribuições e explicações funcionais no pograma de pesquisa. Assim, para alcançar o objetivo, realizamos nosso trabalho em duas vertentes. Na primeira, apresentamos uma discussão sobre o surgimento e o desenvolvimento de Gaia enquanto um programa de pesquisa, as questões epistemológicas suscitadas por ele e suas implicações para a compreensão do sistema Terra. Na segunda vertente, discutimos as atribuições e explicações funcionais na filosofia da biologia, com ênfase para duas teorias: a abordagem etiológica selecionista de Larry Wright e a análise funcional de Robert Cummins. Defendemos que as duas teorias são empreitadas distintas e que não devem ser unificadas numa única abordagem sobre as funções. Isto levanos a apoiar a tese do consenso dualista de Godfrey-Smith. Apresentamos também a crítica de Cummins às abordagens etiológicas selecionistas, as quais ele rotulou de neo-teleologia. Apesar de algumas das críticas de Cummins localizarem corretamente falhas naquela abordagem, outras críticas perdem de vista pontos importantes das abordagens etiológicas de função, que não podem ser deixadas de lado. A partir das críticas de ambos os lados do debate filosófico, a compreensão sobre função na biologia, é sobremaneira enriquecida. Em seguida, a partir das discussões anteriores, nos voltamos especificamente para as atribuições e explicações funcionais em Gaia, construindo uma síntese dos argumentos apresentados nas duas vertentes do trabalho. Buscamos uma solução para a questão teórica investigada a partir da perspectiva sobre as funções de Cummins. Para este filósofo, função é uma capacidade de um ítem à qual recorremos para compreender a realização de uma capacidade do sistema que o contém. Após discutir questões como decomposição e localização em sistemas complexos e em Gaia, aplicamos a teoria de Cummins sobre as funções a um subsistema de Gaia, o sistema proposto pela hipótese CLAW, que interliga algas oceânicas, compostos voláteis de enxofre, nuvens sobre os oceanos e o clima global. O resultado de tal aplicação é um modelo funcional do sistema, onde as capacidades dos componentes são tratadas como as funções destes e explicam, juntamente com a organização do sistema, a realização da capacidade sistêmica em questão, a saber, a produção de nuvens sobre os oceanos. O modelo proposto permite concluir que a análise funcional de Cummins fornece um quadro teórico consistente para a construção de explicações funcionais consistentes em Gaia e pode contribuir também para a superação do problema das explicações teleológicas no programa de pesquisa. Por fim, consideramos as implicações de Gaia para o ensino de ciências, especialmente o de biologia, na medida em que ela já está presente nos livros didáticos de biologia do ensino médio. Além disso, Gaia pode ser uma interessante via de inserção de história e filosofia da ciência no ensino de ciências, assim como pode contribuir para a abordagem de temas ambientais.

Submitted by (edna.saturno@ufrpe.br) on 2016-08-12T11:44:04Z No. of bitstreams: 1 Carlos Geraldo Tenorio Alves.pdf: 1048856 bytes, checksum: 684d39357c3efefb3d89265c5161f5be (MD5) / Made available in DSpace on 2016-08-12T11:44:04Z (GMT). No. of bitstreams: 1 Carlos Geraldo Tenorio Alves.pdf: 1048856 bytes, checksum: 684d39357c3efefb3d89265c5161f5be (MD5) Previous issue date: 2007-02-14 / In the present work the objective was to made a comparative analyses of the lameness in the principal milk breed in the Pernambuco State. To this a attendance was performed of 870 cows of 18 bovine herd of milky aptness, in intensive and semi-intensive regime, with 290 belonging dem six race Holland, 290 dem six race Brow Alpine and 290 of six race Girolanda, in the rural northerly pernambucano. This herd was cataloged im owns cards with clinics data of alls the cases of claw affections, handling (installations, feeding, waterings places, hygiene) and between itself confronted in the total the Holland cows presented 489 lesions (14,05 %), the Brown Alpine cows presented 128 lesions (3,68 %) and the Girolando cows presented 108 (3,10 %). Was observeted that exist a tendency of occurrence increase of claw lesions in the bovines plus specializated to the milk production, in the herd plus bordered, in the whiches itself search a increment of the production, by means the genetic advancement, nutrition, handling, greater concentration of animals in firm ground, rough, hard, factores this that have increase the appearing of the claw afections in the bovines, principaly the milk producer. / No presente trabalho objetivou-se fazer uma análise comparativa da laminite nas principais raças bovinas leiteiras no Estado de Pernambuco. Para tal foi feito o acompanhamento de 870 vacas de 18 rebanhos bovinos de aptidão leiteira, em regime intensivo e semi-intensivo, sendo 290 de seis rebanhos da raça Holandesa, 290 de seis rebanhos da raça Parda Alpina e 290 de seis rebanhos da raça Girolanda, nos municípios do Agreste Setentrional de Pernambuco, rebanhos esses catalogados em fichas próprias com dados clínicos de todos os casos de afecções das unhas, dados de manejo (instalações, alimentação, aguadas, higiene) e comparados entre si. No total as vacas Holandesas apresentaram 489 lesões (14,05 %), as vacas Parda Alpina apresentaram 128 lesões (3,68 %) e as vacas Girolanda apresentaram 108 lesões (3,10 %). Observou-se que existe uma tendência de aumento da ocorrência de lesões das unhas nos bovinos mais especializados para a produção de leite, nos plantéis mais confinados, nos quais se busca um incremento da produção mediante o avanço genético, nutricional e de manejo, maior concentração de animais em pisos firmes, ásperos e duros, fatores estes que elevam o aparecimento das afecções das unhas nos bovinos, principalmente os produtores de leite.

Die subklinische Klauenrehe oder claw horn disruption (CHD) ist von großer wirtschaftlicher Bedeutung für die Rinderhaltung, da sie zu Lahmheiten, Beeinträchtigungen des Allgemeinbefindens sowie einer eingeschränkten Leistungsfähigkeit der Tiere führt. Trotz zahlreicher Untersuchungen sind die pathophysiologischen Grundlagen der CHD noch immer nicht vollständig geklärt. Die derzeitigen Hypothesen weisen auf eine Ischämie in den noch lebensfähigen Epidermisschichten infolge einer veränderten dermalen Mikrozirkulation. Diese hat pathophysiologische Veränderungen zur Folge, die eine Störung der epidermalen Zellproliferation, eine Schädigung der dermo-epidermalen Verbindung sowie eine veränderte Keratinisierung und Hornproduktion umfassen. Von Bedeutung sind daher In-vitro-Ischämiemodelle, um die epidermale Reaktionsmechanismen auf die pathologischen Veränderungen der Dermis zu untersuchen. Ziel in der vorliegenden Arbeit war die Etablierung eines In-vitro-Ischämiemodells auf der Grundlage boviner Keratinozyten aus der Klauenepidermis. Mithilfe dieses Modells sollten die zellulären Pathomechanismen infolge einer Ischämie, einer Hypoxie sowie eines Glukoseentzugs untersucht werden. Des Weiteren stand die Analyse des Differenzierungsverhaltens der Keratinozyten infolge ischämischer, hypoxischer und hypoglykämischer Konditionen im Mittelpunkt. Für die Etablierung des In-vitro-Ischämiemodells diente als Grundlage das oxygen glucose deprivation (OGD)-Modell, das die Untersuchung eines gleichzeitigen Sauerstoff- und Glukosemangels sowie lediglich einer Hypoxie und eines Glukoseentzugs bei bovinen Keratinozyten ermöglichte. Die Versuche wurden in eine Kurzzeitanalyse über 96 Stunden sowie eine Langzeitanalyse über drei Wochen geteilt. Nach erfolgter Exposition wurde die Zellviabilität mittels LDH(Lactatdehydrogenase)- und MTT(3-(4,5-Dimethylhiazol-2-yl)-2,5-diphenyltetrazoliumbromid)-Assay untersucht. Des Weiteren wurde das veränderte Differenzierungsverhalten der Keratinozyten infolge der veränderten Kultivierungsbedingungen mittels Western Blot-Analyse anhand der Involukrin- und Lorikrin-Expression untersucht. Die Keratinozyten zeigten infolge einer OGD nach kurzer Expositionsdauer die höchsten zytotoxischen Effekte, die von einer zeitabhängigen Abnahme der Zellviabilität sowie massiven morphologischen Veränderungen gefolgt wurde. Hypoxische Bedingungen bewirkten eine zeitabhängige Abnahme der Zellviabilität, die erst nach zweiwöchiger Inkubation die größte Zytotoxizität aufwies, sowie eine geringgradig veränderte Zellmorphologie bei Erhaltung des Zellverbands. Der Glukoseentzug bewirkte eine stark verminderte Zellviabilität sowie starke morphologische Zellveränderungen. In der Western Blot-Analyse konnte eine gesteigerte Involukrin- und Lorikrin-Expression infolge einer OGD, einer Hypoxie und eines Glukoseentzugs nachgewiesen werden. In der vorliegenden Arbeit konnte erstmalig ein auf bovinen Keratinozyten basierendes In-vitro-Ischämiemodell etabliert werden, das die Untersuchung zellulärer Mechanismen der Epidermis ermöglichte. Die OGD zeigte den stärksten Einfluss auf die Zellviabilität sowie eine veränderte Zelldifferenzierung der Keratinozyten, was die pathophysiologischen Veränderungen im Rahmen der CHD reflektiert. Die ebenfalls starken Zellveränderungen infolge eines Glukoseentzugs verdeutlichen die Rolle der Glukose im Zellmetabolismus der Keratinozyten. Solch ein epidermaler Glukosemangel ist in Verbindung mit der negativen Energiebilanz der Rinder im peripartalen Zeitraum denkbar. Die Ergebnisse infolge einer Hypoxie verweisen auf vielfältige Adaptationsmechanismen der Keratinozyten an hypoxische Bedingungen, denen sie in der Epidermis in vivo während der Zelldifferenzierung ausgesetzt werden. Damit besitzt das In-vitro-Ischämiemodell ein großes Potenzial für den Einsatz in der Klauenreheforschung, um einerseits die mit einer Ischämie einhergehenden pathologischen Veränderungen der CHD untersuchen zu können. Andererseits liefert das Modell wertvolle Informationen zu den physiologischen Grundlagenmechanismen der Epidermis, die mit der Zelldifferenzierung einhergehen. / The subclinical laminitis or claw horn disruption (CHD) is of great economic importance in the dairy industry as it causes lameness, poor general condition and reduced performance. Despite extensive research efforts, the pathomechanism of CHD remains widely unclear. The current hypotheses on CHD pathogenesis include ischemic alterations of the epidermal keratinocytes resulting from an impaired blood supply. This causes an alteration of cell proliferation, a dermo-epidermal separation and an impaired keratinization and horn production. Therefore, in vitro ischemia models are of critical importance in clarification of the epidermal responses to an altered microcirculation. The aim of this study was the establishment of an in vitro ischemia model based on bovine claw keratinocytes. This in vitro model should enable the investigation of cellular pathomechanisms following exposure to ischemia, hypoxia and glucose deprivation. An additional aim was the analysis of the differentiation pattern of keratinocytes under ischemic, hypoxic and hypoglycaemic conditions. To establish the in vitro ischemia model, the keratinocytes were exposed to oxygen-glucose deprivation (OGD). In addition, this model allowed the parallel examination of hypoxic and hypoglycaemic conditions on bovine claw keratinocytes. The experiments were divided into a short-term analysis over 96h and a long-term analysis over three weeks. Measurement of cell viability was performed by LDH(lactatedehydrogenase) and MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra- zolium bromide) assays. Furthermore, the differentiation pattern of the keratinocytes after exposure to ischemia, hypoxia and glucose deprivation was detected by western blot analysis of the focus on expression of involucrin and loricrin. The highest cytotoxic effect was measured after short exposure to OGD followed by a time-dependent decrease of cell viability and extensive morphological changes of the keratinocytes. Hypoxic conditions lead to a time-dependent decrease of cell viability with the highest cytotoxicity after two weeks. The keratinocytes showed slight changes in cell morphology while maintaining a confluent cell layer. Exposure of keratinocytes to glucose deprivation showed a high decrease of cell viability and strong morphological changes. Furthermore, western blot analysis showed an altered expression pattern with increased involucrin and loricrin levels after exposure to OGD, hypoxia and glucose deprivation. The present study established for the first time an in vitro ischemia model based on bovine claw keratinocytes to study the cellular mechanisms of the epidermis. After exposure to OGD, keratinocytes showed the highest loss in cell viability and an altered cell differentiation. This reflects the pathophysiological changes following epidermal ischemia occurring during the pathogenesis of CHD. The massive cellular alterations after glucose deprivation provide good evidence for the importance of glucose in the cellular metabolism of keratinocytes. An epidermal glucose deficiency may occur in combination with a negative energy balance during peripartal period in cattle. The results of hypoxia show the different adaptive mechanisms of keratinocytes to hypoxic conditions which are present in the epidermis during cell differentiation. Thus, the in vitro ischemia model has a great potential for use in research into CHD pathogenesis and pathomechanisms associated with ischemia. On one side, it is possible to investigate the pathological changes following ischemia during CHD. On the other side, the model offers useful information on physiological response mechanisms of the epidermis that correlate with cell differentiation.