L’entérite nécrotique aviaire causée par Clostridium perfringens est une maladie économiquement dévastatrice et celle-ci est en émergence dans les troupeaux de poulets de chair éliminant l’usage des antibiotiques. À ce jour, aucune alternative en élevage ne permet de prévenir efficacement la maladie et un contrôle par une stratégie vaccinale serait des plus prisé. Une approche par génomique comparative jumelée à la vaccinologie réverse soustractive et comparative identifiant des protéines bactériennes de surface immunogènes figure parmi les approches méthodologiques des plus prometteuses pour le développement rapide d’un vaccin efficace. Une étude génomique comparative réalisée sur 48 souches de C. perfringens provenant de poulets de chair en santé ou affectés par l’entérite nécrotique a permis d’établir que les génomes analysés étaient composés de 155 700 protéines distinctes, où 13% étaient extracellulaires, 65% cytoplasmiques et 22% membranaires. L’évaluation du pouvoir immunogène de ces protéines à l’aide de l’outil de prédiction VaxiJen v.2.0 a permis d’identifier 4 catégories de scores pour les protéines identifiées, allant de 0,5 (seuil minimal recommandé) à 1,5. Les protéines présentant les scores les plus élevés ont été majoritairement associées à des localisations extracellulaires. La combinaison du score d’immunogénicité et de la localisation cellulaire des protéines analysées a mené à la sélection de 12 protéines candidates vaccinales, la plupart d’entre elles étant de fonction hypothétique. Une description plus approfondie de ces protéines permettra de mieux définir leur fonction, d’évaluer leur potentiel antigénique réel en caractérisant leur interaction avec le système immunitaire de la volaille et ultimement, d’évaluer leur rôle probable dans la pathogénie de l’entérite nécrotique. / Avian necrotic enteritis caused by Clostridium perfringens is a disease with a major economical impact, generating losses up to 6 billion dollars for the poultry industry worldwide. This disease appears in broiler chicken flocks that no longer employ the use of antibiotics. To date, no alternative method allows for the efficient prevention of necrotic enteritis (NE) and a control by a vaccinal strategy would be mostly prized. A comparative genomics approach as well as comparative and subtractive reverse vaccinology identifying immunogenic bacterial surface proteins is one of the most promising methodologies for the rapid development of an efficient vaccine. A comparative genomic study was performed on 48 C. perfringens strains isolated from healthy broiler chickens and from broilers affected by necrotic enteritis. From this study, it was established that the genomes analyzed were composed of 155 700 distinct proteins where 13% were predicted to have an extracellular expression, 65% at the cytoplasma level and 22% within the plasma membrane. The evaluation of the immunogenic potential of these proteins was established with the prediction software VaxiJen v2.0 for which a 0.5 threshold score allowed for the identification of four score categories among the identified proteins, from 0.5 to 1.5. For the most part, proteins with the highest scores were associated with an extracellular localisation. The combination of the immunogenicity score and localisation of the analysed proteins led to the selection of 12 vaccinal candidate proteins that were mostly identified as hypothetical. A more in-depth description of these proteins would allow the assessment of their function, the evaluation of their true immunogenic potential by characterizing their interaction with the avian immune system and ultimately, evaluate their probable role in the pathogenesis of necrotic enteritis.

Campylobacter est la principale cause de gastro-entérite bactérienne d’origine alimentaire à travers le monde. Chez les consommateurs, les campylobactérioses d’origine alimentaire sont en grande majorité dues au contact et à la consommation de produits de volaille, le poulet à griller étant particulièrement mis en cause. La contamination de la carcasse se fait souvent lors de l’abattage des oiseaux. Bien que plusieurs données concernant la distribution de Campylobacter à l’abattoir soient disponibles dans certains pays, aucune étude récente visant à décrire la présence et la distribution de ce pathogène, tout au long de la chaîne d’abattage, n'a été réalisée au niveau des établissements d'abattage canadiens. Notre hypothèse était que l’on pouvait identifier des étapes clés d’intervention pour contrôler la contamination par Campylobacter sur les carcasses de volaille à l’abattoir en étudiant la présence de ce pathogène sur les produits de viande et dans l’environnement de production. Il y avait deux objectifs principaux dans cette étude. Premièrement, nous voulions décrire la distribution de Campylobacter lors des différentes étapes de production dans deux établissements de transformation québécois. Deuxièmement, nous voulions déterminer si les moyens de gestion du risque mis en place au moment de l’étude étaient suffisants pour prévenir la contamination du produit de viande destiné au consommateur. Pour répondre à ces objectifs, un oiseau par lot d’élevage a été échantillonné par rinçât de carcasse pour chaque étape suivante de la transformation (n=4) : avant l'abattage, tout juste après la saignée, au transfert entre les chaînes d'abattage et d'éviscération, après l'éviscération et après l’étape du refroidissement dans deux abattoirs québécois. Cette procédure fut répétée pour un total de 379 échantillons de rinçâts de carcasses de poulets de chair qui ont été collectés à l’occasion de multiples visites à l’abattoir et ce, de février à juillet 2017. Un total de 217 échantillons environnementaux pouvant être impliqués dans la contamination croisée des oiseaux ont aussi été récupéré pendant les diverses visites. Les échantillons ont été dilués dans de l'eau peptonée et une identification de Campylobacter par PCR a été faite à l’aide d’amorces spécifiques au gène codant pour l’ARN ribosomal 16S. Les résultats obtenus pour la période étudiée indiquent que la positivité des carcasses de poulets de chair à Campylobacter est significativement plus élevée pour les échantillons effectués l’été comparé au printemps. En revanche, la présence de la bactérie dans l’environnement des abattoirs étudiés apparaît plus élevée durant l’hiver. Puisque la présence de la bactérie sur les carcasses de poulets a diminué tout au long de la chaîne de production, qu’aucune carcasse positive n’a été retrouvée après un refroidissement à l’air et que la positivité des carcasses suite au refroidissement à l’eau était aussi très basse, nos résultats suggèrent, malgré certains enjeux associés à la sensibilité de la méthode d’identification des échantillons positifs, que les mesures actuelles de gestion du risque sont efficaces pour contrôler Campylobacter dans les deux abattoirs québécois suivis. / Campylobacter is responsible of the highest number of bacterial gastroenteritis worldwide. Most diseases in humans attributed to meat can be associated to consumption of or contact with poultry derived products; broiler chicken being involved in the majority of cases. The contamination of carcasses often occurs during the slaughter process. While many studies from various countries reported the distribution of Campylobacter among various critical steps of the slaughter process, none has been published, to our knowledge, in Canada regarding the presence and distribution of this bacterium within the abattoir. Our hypothesis was that it would be possible to identify key steps to control the contamination of carcasses by this bacterium by studying the presence and distribution of Campylobacter on carcasses and within the environment during the slaughter process. This study had two objectives. The first objective was to describe the distribution of Campylobacter within two selected slaughterhouses in Quebec in order to understand which processing step(s) play(s) a critical role in carcasses contamination. In the second objective, we aimed to verify if actual management procedures applied in these abattoirs were efficient in preventing consumer’s exposition. To meet these goals, four birds by production lot, one at each of the following steps (after bleeding, at transfer between killing and evisceration chain, after evisceration and after the cooling process) were sampled for a total of 379 birds from February 2017 to July 2017 in two slaughterhouses located in the province of Quebec. Furthermore, 217 environmental samples were collected during these visits in various sites possibly in contact with birds. Samples were suspended in peptone water and submitted to a PCR assay, using a specific 16S ribosomal probe, for detection of Campylobacter. Overall, for the year of the study, we observed a significantly higher number of positive carcasses in summer compared to spring, while the environmental samples were more often positive in winter compared with summer. Furthermore, our results indicated that the number of positive carcasses decreased over the various processing steps, being either negative (air chilling) or low (water chilling) after the cooling process. Although we experienced some issues associated with the sensitivity of the procedure we used in this study to recover Campylobacter, taken together, these results suggest that the actual management procedures of Campylobacter in studied slaughterhouses are efficient.

Broilers are nearing their genetic potential and nutritional strategies are the primary means to improve their performance. Improving raw material quality, especially soybean meal, could improve broiler performance, health and welfare. Inadequate processing of soybean meal leads to high residual anti-nutritional factors (ANF) which has a negative influence on broiler performance. High trypsin inhibitor content in low- quality soybean meal causes decreased protein digestion and absorption. The main aim of this study was to evaluate the optimal quality of soybean meal for commercial use to promote performance and welfare parameters of broiler chickens. Ten dietary treatments were formulated to the same nutritional specifications, but with different soybean meals that ranged from very high-quality (Treatment 1) to the lowest quality (Treatment 10). The quality of soybean meal was determined using Table 2.1 as target values for each soybean meal quality parameter. Soybean meal quality was evaluated using urease levels (pH change), TIA (trypsin inhibitor activity), Evonik TIA, KOH (potassium hydroxide solubility), Evonik KOH, Evonik PDI (protein dispersibility index) and Evonik PCI (processing conditions indicator). The treatment diets were fed to 4800 broilers that were randomly allocated to 80 pens, each with 60 birds and eight replicates. Over a 35-day growth trial, broiler performance, welfare and physiological traits were measured on a weekly basis. Overall, improved performance was observed with higher-quality soybean meal outperforming the lower-quality soybean meal. High-quality soybean meal showed significantly better feed conversion ratio’s (FCR) and European performance efficiency factor (PEF) throughout the 35-day period, and significantly higher average daily gain (ADG) up until day 21. Bodyweight (BW), feed intake (FI) and mortality showed no significant differences irrespective of soybean meal quality. No significant differences were found in physiological traits namely: pancreas weight as a percentage of bodyweight, pancreas length to bodyweight ratio, gizzard and proventriculus weight as a percentage of bodyweight and gizzard erosion score, (PW%BW, PL:BW, GPV%BW, GE score) irrespective of soybean meal quality. High quality soybean meal showed lower incidence and lower severity of rapid feed passage (RFP) and foot pad dermatitis (FPD). Evonik PCI and urease levels (pH change) showed the strongest correlation to broiler performance, health and welfare. This study suggests using soybean meal with the following quality parameters: urease levels of around 0.05, TIA levels of below 4mg/g, KOH levels of 78-80%, PDI levels of around 15 and PCI levels of around 11. The Evonik PCI and urease (pH change) analyses for soybean meal quality was found to be the easiest and cheapest method and can be recommended as the primary quality assays for commercial feed companies in the future. / Dissertation (BSc (Agric) Animal Science)--University of Pretoria, 2020. / AFGRI / Animal and Wildlife Sciences / BSc (Agric) Animal Science / Restricted

Department of Animal Science / BSCAGR

Thesis (M. Sc. Agriculture (Animal Production)) -- University of Limpopo, 2021 / Two experiments were conducted to determine the effect of replacing soya bean meal with yellow mealworm larvae meal (Tenebrio molitor) in a diet on productivity, gut morphology, carcass characteristics and bone morphometrics of Ross 308 broiler chickens aged one to 42 days. In each experiment, a total of 360 Ross 308 broiler chickens were randomly assigned to the five dietary treatments, each treatment having four replications, and 18 chickens per replicate. Five diets were formulated to contain yellow mealworm replacement levels at 0, 25, 50, 75 and 100% to meet the nutrient requirements of Ross 308 broiler chickens. Data was analysed using the General Linear Model procedures of the Statistical Analysis System, Version 9.3.1 software program. Fisher’s least significant difference (LSD) test was applied for mean separation where there were significant differences (P<0.05). A quadratic regression model was used to determine the levels for optimal responses in the variables measured. The first experiment determined the effect of replacing soya bean meal with yellow mealworm larvae meal on productivity and gut morphology of unsexed Ross 308 broiler chickens aged one to 21 days. Replacement of soya bean meal with yellow mealworm meal in a diet had no effect (p > 0.05) on feed intake, growth rate, FCR, live body weight, ME intake and nitrogen retention of unsexed Ross 308 broiler chickens aged one to 21 days. Replacing soya bean meal with yellow mealworm meal in a diet did not affect (p > 0.05) caecum weight of unsexed Ross 308 broiler chickens. However, replacing soya bean meal with yellow mealworm meal in a diet increased (p < 0.05) gastro intestinal tract, crop, ileum and large intestine weights. Crop and ileum lengths of unsexed Ross 308 broiler chickens aged 21 days were not affected (p > 0.05) by replacement of soya bean meal with yellow mealworm meal in the diet. However, replacing soya bean meal with yellow mealworm meal in a diet increased (p < 0.05) gizzard, caecum and large intestine lengths of unsexed Ross 308 broiler chickens aged 21 days. Yellow mealworm meal in a diet did not affect (p > 0.05) gut organ digesta pH values of unsexed Ross 308 broiler chickens aged 21 days. The second experiment determined the effect of replacing soya bean meal with yellow mealworm meal in a diet on productivity, gut morphology, carcass characteristics and bone morphometrics of Ross 308 broiler chickens aged 22 to 42 days. Replacement of soya bean meal with yellow mealworm meal in a diet did not affect (p > 0.05) growth rate, FCR, ME intake and nitrogen retention of male Ross 308 broiler chickens aged 22 to 42 days. However, replacing soya bean meal with yellow mealworm meal in a diet affected (p < 0.05) feed intake and live body weight of male Ross 308 broiler chickens aged 22 to 42 days. Broiler chickens on diets containing 75 or 100% yellow mealworm meal had higher (p < 0.05) intakes than those on diets containing no yellow mealworm meal. Similarly, male broiler chickens on diets having 50% yellow mealworm meal had higher (p < 0.05) live body weights than those on diets containing no yellow mealworm. Quadratic equations indicated that feed intake and live body weight of male Ross 308 broiler chickens were optimized at yellow mealworm meal replacement levels of 13 and 61%, respectively. The present study showed that replacing soya bean meal with yellow mealworm meal in a diet did not affect (p > 0.05) gut organ digesta pH values, gut organ weights, gut organ lengths, meat colour, meat pH values, bone morphometric values, carcass part weights and meat sensory attributes of male Ross 308 broiler chickens aged 42 days. However, meat from chickens on diets containing yellow mealworm meal was softer (p < 0.05) than meat from chickens on diets having 100% soya bean meal. It is concluded that soya bean meal can be replaced with yellow mealworm larvae meal in a diet at 25, 50, 75 and 100% levels without having adverse effects on production and carcass characteristics of Ross 308 broiler chickens aged one to 42 days

The live production sector of the poultry industry has a growing interest in robotics. Robotics have the possibility to monitor environmental conditions, assess bird welfare, and reduce labor for farm workers and owners. However, interactions of poultry with robotic systems in commercial poultry house environments is largely unknown. Therefore, the goal of this research was to assess the effect of ground and aerial robots on bird stress using avoidance distance (AD) and fleeing speed (FS) as indirect indicators. A low-cost, autonomous robot was also developed to aid in collecting data on environmental conditions in commercial broiler houses. AD and FS were measured for multiple breeds (broilers, brown hens, and white hens) at different bird ages. Poultry-robot AD was greater than poultry-human AD for both broilers and laying hens, indicating that birds tended to avoid the ground robot more than humans. However, birds did become accustomed to the ground robot as reflected by decreasing AD and FS over the trial periods. Aerial drones operated in a commercial broiler house were found to induce a larger AD and higher FS than a moveable sensor package attached to a fixed, overhead rail system. No significant difference was found in the performance of the low-cost, autonomous robot when tested on different substrates (hard tile and litter). However, some differences were found when the robot was operated at different speeds. Results from these studies have provided useful insight into the operation of ground and aerial robots in commercial poultry settings.

The poultry industry is seeking an advanced chilling system that can improve chilling efficiency, microbial safety, and water consumption without compromising meat quality. The objective of this study was to evaluate the effects of sub-zero saline chilling methods on chilling efficiency, breast fillet tenderness and microbial reduction of broiler carcasses. Following evisceration and rinsing, broiler carcasses were randomly assigned to one of three chilling solutions: 1) 0% salt or ice water control (0% NaCl/0.5oC), 2) 3% salt (3% NaCl/-1.8oC), and 3) 4% salt (4% NaCl/-2.41oC) solutions. Broiler carcasses in sub-zero saline solutions reached the target internal temperature of < 4.4 oC in a faster rate than the 0% salt control, reducing the chilling time by 11% and 39 % for 3% NaCl/-1.8oC and 4% NaCl/-2.41oC solutions, respectively. There was no significant difference in breast fillet pH, regardless of chilling treatment (P < 0.05). However, the breast fillets from sub-zero saline solutions showed higher R-value and longer sarcomere length than those of control fillets (P < 0.05). Breast fillets excised from carcasses in 4% NaCl/2.41oC were significantly tenderized more than the control fillets, with an intermediate tenderness observed for the fillets from 3% NaCl/-1.8oC (P< 0.05). Before chilling, broiler carcasses contained mesophilic aerobic bacteria (MAB), Escherichia coli(E. coli), and total coliforms for 3.81, 0.78, and 1.86 log colony forming unit (CFU)/g, respectively. After chilling, the populations of E. coliand total coliforms were significantly reduced on the carcasses in 3% NaCl/-1.8oC and 4% NaCl/-2.41oCcompared to the control fillets (P< 0.05). There was no significant difference for MAB populations, regardless of treatment. Based on these results, chilling of broiler carcasses in 4% NaCl/-2.4 °C solution seems to be the best choice to improve chilling efficiency, meat tenderness, and microbial reduction compared to the control (0% NaCl/0.5ºC) and 3% NaCl/-1.8oCsolutions.

Thesis (M.Sc. (Animal Production)) -- University of Limpopo, 2023 / Two experiments were conducted to determine the effect of citric acid inclusion level in the diet on growth performance, carcass weight, tibia bone breaking strength and ash content of male Ross 308 broiler chickens aged one to 35 days. The first experiment determined the effect of citric acid inclusion level in the diet on growth performance traits of male Ross 308 broiler chickens aged one to 21 days. The experiment commenced with 200 male day-old Ross 308 broiler chickens with an initial average live weight of 40±1.6g per chick. The chicks were assigned to five treatment groups in a completely randomized design, each replicated five times, and each replicate having ten chicks. The citric acid inclusion levels were at 0, 12.5, 25 or 50g per kg DM of feed. The second experiment determined the effect of citric acid inclusion level in the diet on growth performance, carcass weight, tibia bone breaking strength and ash content traits of male Ross 308 broiler chickens aged 22 to 35 days. The experiment commenced with 180 male Ross 308 broiler chickens aged 22 days. The chickens were assigned to four treatment groups, each having three replicate pens of eight chickens per replicate in a completely randomized design. Data was analysed using the General Linear model (GLM) procedures of the Statistical Analysis of System, version 9.3.1 software program. Where there were significant differences (P<0.05) between the treatment means, Tukey Multiple Comparison Test was used for mean separation. Citric acid inclusion in the starter diets improved (P<0.05) live weight and growth rate of male Ross 308 broiler chickens aged one to 21 days. Citric acid inclusion in the starter diets did not affect (P>0.05) daily feed intake, body weight gain and feed conversion ratio of male Ross 308 broiler chickens aged one to 21 days. The inclusion of citric acid did affect (P<0.05) live weight, body weight gain, feed conversion ratio and growth rate of chickens aged 22 to 35 days. Citric acid inclusion levels used in the present study influenced (P<0.05) DM and CP digestibility, ME intake and N-retention of male broiler chickens aged 22 to 35 days. The results of the current study showed that citric acid inclusion in a diet improved (P<0.05) chicken bone morphology. Thus, positive relationships were observed between citric acid inclusion level and right tibia bone weight, diameter, calcium, phosphorous and Magnesium contents of chicken bones aged 35 days. There were positive relationships between citric acid inclusion level and breast weight of male Ross 308 broiler chickens aged 35 days. Further studies are recommended to ascertain these findings. / National Research Foundation (NRF)

Two metabolism trials were conducted with 15 wethers surgically equipped with duodenal and ileal cannulas to study the absorption of P and certain other minerals from swine waste and broiler litter. The effect of source and level of P on rumen cellulytic bacterial populations was also determined. Animals were fed a low P basal diet until serum inorganic P averaged 5.5 mg/dl, then randomly assigned to the following diets: low P basal alone, or supplemented with swine waste, broiler litter, dicalcium phosphate, or soybean meal. Trials consisted of a 7-d preliminary period, a 7-d collection of urine and feces and a 6-d sampling of duodenal and ileal digesta, and feces. Animals fed the waste diets tended to absorb more P than those fed the conventional supplements. Calculated by difference, sheep absorbed more P from swine waste and broiler litter than from dicalcium phosphate and soybean meal (P< .1). Less Ca was absorbed from the waste diets than from the conventionally supplemented diets (P< .05). Expressed as g/d, there was no difference in Mg absorption between waste and conventional diets. Sheep fed waste tended to digest more dry matter and a higher percentage of ADF in the large intestine. Lignin was primarily digested in the large intestine of all sheep. More cellulytic bacteria were isolated from the rumen of sheep fed the supplemented diets (P< .05). Both P intake and P recycling appear to be important influences on cellulytic bacteria in the rumen. Both broiler litter and swine waste appear to be good sources of P and Mg for ruminants. / Ph. D.

L’utilisation d’antimicrobiens (UAM) dans les élevages de volailles est essentielle pour contrôler les maladies et les agents pathogènes. Cependant, l’UAM en production animale a été associée à l’émergence de la résistance aux antimicrobiens (RAM). La surveillance et l’utilisation judicieuse des antimicrobiens dans les fermes constituent des priorités impliquant la mise en place de systèmes de surveillance incluant des indicateurs permettant de quantifier de manière précise l’UAM dans les élevages. Notre étude vise à calculer 3 indicateurs différents de l’utilisation des antimicrobiens administrés par l’aliment dans les élevages de poulets de chair au Québec de 2017 à 2022, soit le milligrammes/Population correction unité (mg/PCU), le nombre de doses journalières définies canadiennes pour les animaux sur 1 000 poulets-jours à risque (nDDDvetCA/1 000 poulets-jours à risque) et le nDDDvetCA/1 000 poulets-jours à risque basé sur un poids estimé réel au moment du traitement, et à comparer les résultats obtenus par ces différentes méthodes de calculs. Les données sur l’UAM dans les aliments et la quantité de moulée consommée ont été obtenues des audits réalisés par les Éleveurs de volailles du Québec sur des fermes sélectionnées aléatoirement. La grille de poulets Ross a été utilisée pour estimer les poids des oiseaux au moment du traitement ainsi que les quantités d’aliments consommées quotidiennement, permettant de calculer le nDDDvetCA/1 000 poulets-jours à risque basé sur le poids estimé réel au moment du traitement dans chaque lot. Les résultats obtenus ont été comparés à ceux calculés en mg/PCU et nDDDvetCA/1 000 poulets-jour à risque (calculé avec un poids moyen standard de 1 kg). Vingt IAA administrés dans l’aliment des lots ont été identifiés. Les trois les plus utilisés étaient la bacitracine (51,6 %, n = 772 troupeaux), le monensin (43,9 %), et la nicarbazine (39,5 %). Les quantités moyennes d’antimicrobiens utilisés étaient de 122 mg/PCU, 512 nDDDvetCA/1 000 poulets-jours à risque et 507 nDDDvetCA/1 000 poulets-jours à risque basé sur un poids estimé réel au moment du traitement. Une corrélation élevée a été observée entre le nDDDvetCA/1 000 poulets-jours à risque et celui basé sur un poids estimé réel au moment du traitement. Les lots avec une forte UAM selon le nDDDvetCA/1 000 poulets-jours à risque basé sur un poids estimé réel au moment du traitement étaient également forts utilisateurs selon le mg/PCU et en nDDDvetCA/1 000 poulets-jours à risque. Le nDDDvetCA basé sur le poids réel au moment du traitement pourrait être utilisé pour identifier les troupeaux les plus gros UAM, car il prend en compte la croissance rapide des poulets de chair. Cela permet d’éviter la surestimation ou la sous-estimation des AAI administrés respectivement tôt ou tard pendant le cycle de production ce qui peut se produire en utilisant le nDDDvetCA/1000 poulets-jours à risque calculé avec un poids moyen standard de 1 kg pour les poulets de chair. / The use of antimicrobials (AMU) in poultry farms is essential for controlling diseases and pathogens. However, AMU in animal production has been associated with the emergence of antimicrobial resistance (AMR). Surveillance and judicious use of antimicrobials on farms are priorities involving the implementation of surveillance systems including indicators to accurately quantify AMU in farms. Our study aims to calculate three different indicators of antimicrobial use administered through feed in broiler chicken farms in Quebec from 2017 to 2022: milligrams per Population Correction Unit (mg/PCU), the number of Canadian Defined Daily Doses for animals per 1 000 chicken-days at risk (nDDDvetCA/1 000 chicken-days at risk), and the nDDDvetCA/1 000 chicken-days at risk based on an estimated actual bird weight at treatment, and to compare the results obtained by these different calculation methods, and to compare the results obtained by these different calculation methods. Data on AMU in feed and the quantity of feed consumed were obtained from audits conducted by the Éleveurs de volailles du Québec on randomly selected farms. The Ross Broilers Management Handbook was used to estimate bird weights at treatment as well as daily feed consumption, allowing calculation of nDDDvetCA/1 000 chicken-days at risk based on the estimated actual weight at treatment in each flock. The results obtained were compared to those calculated in mg/PCU and nDDDvetCA/1 000 chicken-days at risk. Twenty antimicrobial active ingredients (AAI) administered in feed were identified. The three most used were bacitracin (51.6%, n = 772 flocks), monensin (43.9%), and nicarbazine (39.5%). The average quantities of antimicrobials used were 122 mg/PCU, 512 nDDDvetCA/1 000 chicken-days at risk, and 507 nDDDvetCA/1 000 chicken-days at risk based on estimated actual weight at treatment. A high correlation was observed between nDDDvetCA/1 000 chicken-days at risk and that based on estimated actual weight at treatment. Flocks with high AMU according to nDDDvetCA/1 000 chicken-days at risk based on estimated actual weight at treatment were also high users according to mg/PCU and nDDDvetCA/1 000 chicken-days at risk. The nDDDvetCA based on actual weight could be used to identify the highest user flocks since it takes into account the rapid growth of broiler chickens. This approach allows for avoiding the overestimation or underestimation of AAI administered early or late in the grow-out cycle, respectively, which can occur when using the nDDDvetCA/1000 chicken-days at risk calculated with a standard weight of 1 kg for broiler chicken.