2000. A study on the variation of feed efficiency in station tested bulls. Can. J. Anim. Sci. 80: [435][436][437][438][439][440][441]. The records of 282 young beef bulls from eight breeds tested from November 1981 to April 1987 at the Ellerslie Bull Test Station, Alberta, Canada, were used to study the variation in feed efficiency among young performance-tested bulls. Considerable variation existed among the animals in both residual metabolizable energy consumption and residual dry matter consumption. The heritability estimates for residual metabolizable energy consumption and residual dry matter consumption were 0.33 and 0.29, respectively. In addition, residual metabolizable energy consumption and residual dry matter consumption were moderately correlated (r = 0.43) with conventional feed-to-gain ratio, indicating that conventional feed-to-gain ratio only accounted for 18% of the variation in residual metabolizable energy consumption or residual dry matter consumption. It was, therefore, worthwhile to use residual metabolizable energy consumption or residual dry matter consumption as separate measures of feed efficiency. For rapid improvement in feed efficiency in beef cattle, selection pressure should be applied to both growth traits and residual energy consumption or residual dry matter consumption. Multi-trait optimum restricted selection indices and similar selection procedures may serve as useful means in balanced selection programs to improve the productivity of beef cattle.Key words: Feed efficiency, residual ME consumption, beef bulls Liu, M. F., Goonewardene, L. A., Bailey, D. R. C., Basarab, J. A., Kemp, R. A., Arthur, P. F., Okine, E. K. et Makarechian, M. 2000. Étude de la variabilité de l'efficacité alimentaire chez les taureaux à viande testés en station. Can. J. Anim. Sci. 80: 435-441. Les fiches de 282 taurillons de 8 races de type à viande testés de novembre 1981 à avril 1987 à la station d'Ellerslie (Alberta) ont servi à un examen de la variation de l'efficacité alimentaire manifestée parmi les taurillons. Nous avons ainsi pu observer un degré élevé de variation de la consommation résiduelle, à la fois d'énergie métabolisable et de matière sèche parmi les animaux. Les valeurs d'héritabilité pour les deux caractères étaient respectivement, de 0,33 et 0,29. En outre, les deux caractères affichaient une corrélation modérée (r = 0,43) avec l'indice de consommation classique, démontrant que ces derniers indices ne prenaient en compte que 18 % seulement de la variation affectant les deux facteurs de consommation résiduelle. Il vaut donc la peine d'utiliser l'un ou l'autre de ces facteurs séparément comme mesure de l'efficacité alimentaire. Si l'on veut améliorer rapidement l'efficacité alimentaire chez les bovins à viande, la sélection devrait porter à la fois sur les caractères de croissance et sur la consommation résiduelle d'énergie ou celle de matière sèche. Les indices composites de sélection restreinte optimale ou de techniques de sélection du même genre seraient des outils utiles dans les p...

No abstract

Records of 547, 2-yr-old heifers of three breed groups were used to evaluate the relative influence of dam's body and pelvic measurements, calf birth weight, sire birth weight and some relative measures (ratios) of calf birth weight and dam weight at calving on calving difficulty. The data were analyzed by regression and least squares procedures. The full model explained 32.5% of the variation in calving difficulty score. The linear effect of calf birth weight was the most important variable, accounting for 17.8% reduction in the coefficient of determination, and together with dam weight at calving and the quadratic effect of calf birth weight it accounted for 92% for all the variation explained by the full model. Dam weight at calving was negatively related to calving difficulty. Breed, year and sex of calf did not influence calving difficulty score, except when the calf birth weight or dam weight or both were excluded from the model. When calf birth weight was expressed as a ratio of the dam's weight at calving, hip height and pelvic measurements, the total model explained 34.8% of the variation in calving difficulty score. The ratio of calf birth weight to dam weight was the most important variable (R2 = 26.8%). Ratios of calf to dam weight at calving and calf weight to the vertical pelvic diameter (R2 = 29.3%) were the only significant factors when the effects of calf birth weight and dam weight were removed from the model. Pelvic measurements, on their own, did not influence calving difficulty score in this study (P greater than .1), but small pelvic dimensions tended to be associated with higher calving difficulty scores.

. 1999. Stucture of a dynamic simulation model for beef cattle production systems. Can. J. Anim. Sci. 79: [409][410][411][412][413][414][415][416][417]. A dynamic deterministic model for simulating beef cattle production systems is developed to evaluate the effects of production traits and management strategies on the bioeconomic efficiency of beef production systems. The model, named Alberta Beef Production Simulation System (ABPSS), is composed of four major submodels: herd inventory, nutrient requirement, forage production, and economic submodels. The herd inventory submodel is used to simulate population dynamics and feed requirements in the herd. The nutrient requirements submodel is mainly based on the 1996 version of the National Research Council (NRC). It is used to evaluate nutrients and feed requirements for calves and cows depending on their physiological status (maintenance, growth, lactation and gestation) and the climatic condition. The forage production submodel is used to predict forage growth rate, cattle grazing rate, available forage biomass and total hectares required for grazing. The economic submodel measures bioeconomic efficiency, as net return per cow, by subtracting total cost from total return. The nutrient requirements predicted by ABPSS were compared with those recommended by the NRC for testing. The results that were predicted by the NRC model and ABPSS model were similar, as expected. Sensitivity analyses showed that cow mature weight, milk production, calf weaning weight and feed prices were the most critical input parameters in the model. It must be noted that the model was developed based on available experimental results and data from the literature and, due to the unavailability of a suitable data set, the model could not be validated. We suggest that the ABPSS has the potential for providing a useful method for simultaneous consideration of many factors in an integrated system, which could be helpful to beef cattle extension specialists and cow-calf production managers for assessing the potential effects of different management and selection strategies on bioeconomic efficiency. Key words:Beef cattle, simulation and modelling, production system, optimization Pang, H., Makarechian, M., Basarab, J. A. et Berg, R. T. 1999. Structure d'un modèle en simulation dynamique applicable aux systèmes de production de bovins à viande. Can. J. Anim. Sci. 79: 409-417. Nous avons mis au point un modèle déter-ministe dynamique de simulation des systèmes de production de bovins à viande, pour évaluer les effets des caractères de production et les protocoles de gestion sur l'efficience bioéconomique de ces systèmes. Désigné par le nom de «Alberta Beef Production Simulation System» (ABPSS), il comprend quatre grandes composantes : inventaire du troupeau, besoins en nutriments, production fourragère et économie. La première composante est utilisée pour simuler l'évolution des effectifs et les besoins en aliments du troupeau. La composante «besoins nutritionnels», essentiellement basée sur la vers...

No abstract