<p>  </p> <p>In commercial settings, piglet weaning and transportation occur concurrently due to the expansive application of multi-site production systems across the United States and the combination of these events can be defined as an early life stressor. Early life stress is known to reduce pig performance, efficiency, and immune resilience contributing to reduced welfare and increased production losses. To combat the deleterious effects of stress on pigs, the essential amino acid tryptophan (Trp) supplemented above current National Research Council (NRC 2012) recommended levels, improves neuroendocrine responses to stress, lowers plasma cortisol and norepinephrine concentrations, and improves hypothalamic-pituitary-adrenal axis recovery time following stress. However, there are discrepancies concerning the Trp requirement for nursery pigs, suggesting the 2012 recommendations for Trp may be inaccurate for optimizing growth performance and health in modern pigs. Three experiments were conducted to determine the effects of supplemented standard ileal digestible Trp above NRC (2012) recommended levels on performance, feed efficiency, immune vigor, and stress tolerance. The objective of experiment 1 was to eliminate or reduce short- and long-term, transport-induced reductions in piglet feed efficiency and growth by supplementing Trp above NRC (2012) recommendations pre-weaning and/or during the nursery phase. An oral gavage of Trp or a control milk carrier was provided to pre-allotted piglets beginning at day 5 of lactation and continuing to weaning. At weaning all pigs were blocked by sex, weaning weight and pre-wean treatment and randomly assigned to transport and post-wean treatments. Pigs were fed in four nursery phases with diets containing 1X or 2X NRC recommended concentrations of SID Trp and a common grower diet fed in 6 phases during the grow-finish period. At market, loin characteristics were measured via ultrasound and carcass data was collected from the packing plant. Pre-weaning Trp supplementation had no effect on pre-weaning growth performance; however, post-wean Trp increased overall body weight and average daily gain in nursery pigs when Trp was supplemented pre-wean. The objective for experiment 2 was to mitigate the adverse effects of early life transport stress on subsequent immune challenges by providing supplemental Trp during the nursery period. At weaning, pigs were transported for 8 hours and assigned to treatments of vaccine-induced immune challenge and dietary treatment. Pigs were fed standard nursery diets, in four phases, over 35 days with pigs receiving 1X or 2X the NRC (2012) recommended Trp concentration. Half the pigs on each dietary treatment were subjected to a 3-wk vaccine challenge consisting of circovirus, mycoplasma, and influenza vaccines administered in wk 2, 3, and 4 post-wean, respectively. At market, loin characteristics were measured via ultrasound and carcass data was collected.  At the culmination of the nursery period, unchallenged pigs supplemented with Trp were heavier compared to control pigs. This resulted from an overall improvement in average daily gain for 2X Trp fed pigs. However, increasing Trp did not affect market weight, loin eye area, or lean percent in market pigs, although 2X Trp increased back fat. The objective of experiment 3 was to determine what ratio of SID tryptophan, relative to lysine, maximizes growth performance and feed efficiency in weaned pigs during the nursery period. Pigs were blocked by sex and weaning weight and randomly allotted to one of five dietary treatments with Trp increasing stepwise by 0.33%-units, respectively. Pigs were fed standard nursery diets, in four phases, over 35 days with pigs receiving 1X, 1.33X, 1.66X, 2X, or 2.33X the NRC (2012) recommended Trp concentration.  Overall, there were no differences in performance or efficiency across dietary treatments during a 35-day nursery period in unstressed healthy pigs.  In conclusion, increasing Trp in swine diets prior to and/or following stress events can mitigate stress-related perturbations in performance and efficiency.      </p>

Ce mémoire examine les perceptions et les pratiques de travail sécuritaires des producteurs agricoles au début de la pandémie de la COVID-19 ainsi que les différents défis rencontrés en matière de santé et de sécurité du travail. La recherche vise à comprendre les facteurs individuels (p.ex. niveau de connaissances) et contextuels (c.-à-d. l’environnement immédiat de travail, l’entreprise agricole, le secteur d’activité agricole) ayant influencé la perception du risque et les pratiques de travail sécuritaires adoptées par des producteurs agricoles en marge de la crise de la COVID-19. Pour ce faire, des entretiens semi-dirigés ont été effectués d’auprès d’éleveurs de porcs (n=20) au début de la pandémie de la COVID-19. Ces entretiens font partie du volet qualitatif de l’étude Éleveurs de porcs en santé (Beauregard et al., 2023). De ce volet, onze entretiens ont été analysés grâce à une combinaison des deux modèles théoriques, soit le modèle des croyances relatives à la santé (HBM) et la théorie du comportement planifié (TPB). Des sources documentaires publiques diffusées par treize acteurs clés issus de différents milieux (p.ex. gouvernemental, mouvement associatif agricole) visant à appuyer les travailleurs et les producteurs agricoles dans la prévention de la transmission de la COVID-19 ont aussi été examinées en complément. L’analyse des sources documentaires a permis de dégager trois thèmes portant sur les incitatifs à l’action : 1) sensibiliser et informer; 2) agir en prévention primaire à la ferme ; et 3) intervenir en prévention tertiaire en cas d’infection et appuie le constat selon lequel des incitatifs à l’action multiples ont été mobilisés pour stimuler une gestion efficace de la COVID-19 à la ferme. On constate que les acteurs clés ont bien adopté une communication de crise axée sur les risques et les soins afin de prévenir le risque d’infection et de propagation du SARS-CoV-2. L’analyse des entretiens semi-dirigés précise que les éleveurs ont utilisé les sources documentaires et les recommandations de la santé publique provinciale ou fédérale pour se renseigner sur la nature de la COVID-19 et les pratiques de travail sécuritaires à adopter sur leur ferme. En plus, chaque composante analytique de la perception individuelle du risque conceptualisée par les deux modèles théoriques se retrouve dans l’analyse globales des entretiens semi-dirigés, permettant d’une part d’éclairer pertinemment des éléments de contexte des pratiques de travail sécuritaires, et d’autre part confirmant l’apport important de chaque élément analytique pour expliquer l’adoption des pratiques de travail sécuritaires adoptées par les éleveurs en marge de la COVID-19. / This thesis aims to understand the individual (e.g., level of knowledge) and contextual (e.g., immediate work environment, farm business, agricultural activity sector) factors that influenced the risk perception and safety practices adopted by swine producers from the province of Quebec on the sidelines of the COVID-19 crisis. To do this, semi-directed interviews were carried out with swine producers at the start of the COVID-19 pandemic. These interviews are part of the qualitative component of the Healthy Swine Producers study (Beauregard et al., 2023). From this component, eleven (11) interviews were analyzed using a combination of two theoretical models, namely the Health Belief Model (HBM) and the Theory of Planned Behavior (TPB). Public documentary sources disseminated by thirteen (13) key actors from different backgrounds (e.g. government, agricultural associative movement) aimed at supporting workers and producers in preventing the transmission of COVID-19 were also examined in addition to our interviews. The main results emanating from the analysis of documentary sources is the identification of three different themes relating to incentives to action, which are as follows: 1) raise awareness and inform; 2) act in primary prevention on the farm; and 3) intervene in tertiary prevention in the event of infection and supports the observation that multiple incentives to action have been mobilized to stimulate effective management of COVID-19 on the farm. We can see that the key actors have indeed adopted crisis communication (on risks and care communication) to help prevent the risk of infection and spread of SARS-CoV-2. The analysis of the semi-structured interviews allows us to learn that breeders have used documentary sources and provincial or federal public health recommendations to learn about the nature of COVID-19 and the safety practices to adopt on their farm. In addition, each analytical component of the individual perception of risk conceptualized by the two theoretical models is found in the global analysis of the semi-structured interviews, making it possible to relevantly shed light on elements of the context of safety practices, thus confirming the important contribution of each analytical element to explain the adoption of safety practices by farmers on the sidelines of COVID-19.