The effects of induced subacute ruminal acidosis (SARA) using grain pellet-based (GPI) and alfalfa pellet-based diet models on systemic immunological parameters were evaluated in nonlactating Holstein cows. The systemic immunological parameters analysed in this study included rectal temperature, blood cell leukogram, expression of lipopolysaccharide (LPS) recognition receptors on leukocytic cells, and plasma and serum proteins. Also, blood biochemistry was analysed. There were no significant differences in rectal temperature, blood cell leukogram, expression of LPS recognition receptors and fibrinogen or haptoglobin concentrations between control and SARA induction treatments. Concentrations of serum amyloid A and lipopolysaccharide-binding protein increased while total protein concentrations decreased in response to GPI SARA compared to control. Blood glucose and urea concentrations increased and decreased, respectively, with GPI SARA treatment. Grain pellet-induced SARA resulted in changes to serum proteins and acute phase proteins but did not affect other systemic immunological parameters suggesting a localized inflammatory response was initiated.

The effects of induced subacute ruminal acidosis (SARA) using grain pellet-based (GPI) and alfalfa pellet-based diet models on systemic immunological parameters were evaluated in nonlactating Holstein cows. The systemic immunological parameters analysed in this study included rectal temperature, blood cell leukogram, expression of lipopolysaccharide (LPS) recognition receptors on leukocytic cells, and plasma and serum proteins. Also, blood biochemistry was analysed. There were no significant differences in rectal temperature, blood cell leukogram, expression of LPS recognition receptors and fibrinogen or haptoglobin concentrations between control and SARA induction treatments. Concentrations of serum amyloid A and lipopolysaccharide-binding protein increased while total protein concentrations decreased in response to GPI SARA compared to control. Blood glucose and urea concentrations increased and decreased, respectively, with GPI SARA treatment. Grain pellet-induced SARA resulted in changes to serum proteins and acute phase proteins but did not affect other systemic immunological parameters suggesting a localized inflammatory response was initiated.

L'acidose ruminale latente (ou acidose sub-clinique) est une préoccupation majeure pour la nutrition des ruminants à haut potentiel de production. Cet état se caractérise par une instabilité du microbiote et des fermentations ruminales qui s’orientent variablement vers le propionate et/ou le butyrate. L’une des stratégies de prévention de l’acidose latente consiste à distribuer dans l’alimentation des ruminants des probiotiques capables de rééquilibrer le microbiote et les fermentations ruminales (dans un sens favorable pour l’animal). L’analyse de la bibliographie montre toutefois que l’effet des probiotiques, et plus particulièrement des bactéries probiotiques (BP), est variable et parfois contradictoire ce qui serait probablement lié à l’instabilité du microbiote. Afin d’étudier la possibilité de prévenir l’acidose latente par les bactéries propioniques et/ou lactiques, nous avons émis l’hypothèse que leur efficacité dépend des orientations fermentaires dans le rumen. Des acidoses latentes butyrique et propionique caractérisées par des profils fermentaires et microbiens distincts ont été développées chez le mouton non productif et la vache laitière pour étudier l’effet et le mode d’action de la bactérie propionique P63 seule ou associée aux lactobacilles Lb. plantarum ou Lb. rhamnosus (P63, Lp + P63 et Lr + P63) sur le fonctionnement de l’écosystème ruminal et les performances animales. Chez le mouton en situation d’acidose propionique, les BP utilisées ont amélioré le pH ruminal via une réduction de la proportion en lactobacilles. Chez la vache laitière, la stabilisation du pH a été associée à une moindre disponibilité en hydrogène susceptible d’être transformé en protons, suite à une augmentation de la propionogenèse et/ou de la densité bactérienne, deux voies consommatrices d’hydrogène. Au cours de l’acidose latente butyrique, l’amélioration du pH n’a été observée que chez les moutons supplémentés avec Lp + P63. Cet effet semblait être dû à une diminution des acides gras volatils et de la proportion en S. bovis mais aussi à un pH initial faible (pH < 5,5) probablement optimal pour l’action des BP ; ce qui n’était pas le cas chez les vaches pour lesquelles le pH initial était compris entre 5,9 et 6,1. En revanche, l’efficacité digestive a été augmentée par l’association de P63 aux lactobacilles chez la vache laitière. L’association Lp + P63 a augmenté les activités fibrolytiques (cellulase, xylanase) et la digestibilité de la matière organique, tandis que Lr + P63 a amélioré la digestion des fibres et a diminué la production de méthane de 25%. Nous n’avons pas observé d’effet sur les performances zootechniques, ce qui serait probablement dû au dispositif expérimental en carré Latin qui n’est peut-être pas optimal pour mettre en évidence l’effet des BP. Nos résultats sont les premiers à démontrer l’efficacité des bactéries probiotiques pour sécuriser et/ou améliorer la digestion des rations et réduire la production de méthane chez le ruminant en acidose, et l’association de P63 avec les souches de Lactobacillus sont les plus efficaces. Enfin, nous avons validé notre hypothèse selon laquelle l’effet et le mode d’action des bactéries probiotiques pour prévenir l’acidose dépendent des orientations fermentaires dans le rumen. / Subacute ruminal acidosis (SARA) is a major concern for the nutrition of high-producing ruminants. This digestive disorder is characterized by the instability of the microbial ecosystem and fermentations which are oriented towards propionate and/or butyrate at the expense of acetate (propionic or butyric SARA). Among the strategies used to prevent SARA, supplementation with direct-fed microbials (DFMs) is thought to be able to balance the ruminal microbiota and fermentation. The analysis of the literature shows that the effect of DFMs, especially bacterial ones, is variable and sometimes contradictory which is probably related to the instability of the microbiota. To investigate the possibility of preventing SARA by propionibacteria and/or lactobacilli based DFMs, we hypothesized that their effectiveness depends on the ruminal fermentation patterns. Butyric and propionic SARA, characterized by distinct microbial and fermentation profiles, have been developed in non-productive sheep and lactating dairy cows to investigate the effects and mode of action of the Propionibacterium P63 alone or in conjunction with the lactobacilli strains Lb. plantarum or Lb. rhamnosus (P63, P63 and Lp + Lr + P63) on the ruminal ecosystem and animal performances. During the propionic SARA induced in sheep, the DFMs used increased the ruminal pH with a concomitant reduction in the lactobacilli population. In dairy cows, the pH stabilization was associated with a lower availability of hydrogen capable of being transformed into protons, following a stimulation of propionogenesis and/or bacterial growth that consume hydrogen. During butyric SARA, improvement in pH was observed only in sheep supplemented with Lp + P63. This effect appeared to be due to a decrease in VFA production and S. bovis proportion. Moreover, the lower initial pH (pH <5.5) was probably optimal for DFMs action, which was not the case for the dairy cows for which the initial pH was between 5.9 and 6.1. For the dairy cows, diet digestion was improved when P63 and lactobacilli association were fed. Indeed, Lp + P63 increased the fibrolytic activities (cellulase, xylanase) and digestibility of organic matter, while Lr + P63 improved fiber digestion and decreased methane production by 25%. We did not observe any effect on animal performances, which was probably due to the Latin square design that is not the best to evaluate the DFMs effects on animal performances. Our results are the first to demonstrate the effectiveness of bacterial DFMs to secure and/or improve diet digestion and reduce methane production in ruminants. Moreover, it seems that the association of P63 with the lactobacilli strains is more effective. Finally, we validated our hypothesis that the effect and mode of action of bacterial DFMs to prevent SARA is conditioned by ruminal fermentation patterns.

This work helps to determine the extent of immune system involvement in the adaptive response to subacute ruminal acidosis (SARA) in three parts. The first (Chapter 2) uses non-lactating cows to study specific changes in inflammatory protein expression in which SARA is created. The second (Chapter 3), uses the same model as Chapter 2. However, in this case, lactating cows are used to help establish the time course for adaptation to acidosis. The third part (Chapter 4) delineates the genomic changes that occur in the rumen epithelium when a therapeutic intervention is introduced using exogenous supplemental butyrate. In the first experiment, the expression of the extracellular matrix (ECM) proteins type IV collagen and laminin β1 decreased, and the monocarboxylate transporter MCT1, increased during the acidotic challenge. Nuclear factor of activated T-cells, NFATc2, and tumour necrosis factor alpha (TNF-α) decreased while interleukin-1 beta (IL-1β) increased during the experimental treatment period. Chapter 3 measured lipopolysaccharide (LPS) and its carrier, LPS binding protein, LBP, which were found to be elevated due to SARA. Moreover, NFATc2 was reduced during this period. Exogenous butyrate resulted in increased plasma LBP, plasma beta hydroxyl butyrate (BHBA), and ruminal butyrate. Milk parameters (total protein and fat) were unaffected by treatment, as were rumen LPS, acetate, valerate, isovalerate, and isobutyrate. Moreover, exogenous butyrate increased gene transcription of genes involved in non-specific host defences (NHSD) such as mucin, and remodelling (RM), such as matrix metallopeptidase 16 (MMP16), and decreased the transcription of genes of the immune response (IR), such as nuclear factor kappa B2 (NFκB2). Together, these three experiments have demonstrated that although wound healing is mediated by the immune system in more severe models of epithelial damage, our model of SARA did not involve full-thickness, penetrating lesions and hence did not involve the systemic immune system to such a degree than was previously thought. In addition, we were able to demonstrate that the addition of butyrate to this model of grain-induced acidosis was beneficial, as it decreased the local inflammatory response and helped the epithelium adapt to its harsher environment. / Agriculture and Agri-Food Canada, the National Sciences and Engineering Council of Canada (NSERC), the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), the Canadian Dairy Commission (CDC), and the Dairy Farmers of Ontario (DFO).

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