First-week mortality is an important performance index as well as an important welfare indicator. The aim of the present study was to identify internal (individual-dependent) and external (management or environmental) factors that could influence the cumulative first-week mortality of broilers. To carry out this study, field data obtained from a hatchery company were used, in which 2267 flocks of broiler chicks (from 2015 to 2018), were analyzed. A generalized linear mixed model was used to analyze the data. Farm ID and house by farm were incorporated as random effects. The Odds Ratio was estimated for each factor, determining the effect of each explanatory variable. First-week mortality was significantly related to breeder age (p < 0.0001), chick gender (p < 0.0001) and breed (p < 0.0001) as internal factors, and type of broiler house (p = 0.0129), presence or absence of drip cup (p < 0.0001), egg storage (p < 0.0001), study year (p < 0.0001) and season (p < 0.0001) as external factors. Therefore, these factors should be considered in the decision making of poultry breeding companies, in order to reduce possible welfare problems and increase productive performance.

The present study had 2 objectives: the first was to analyze the possible impact of transport on weight loss and mortality during transport, and first-week mortality. The second was to monitor the environmental condition (i.e., temperature, humidity, and so on) variability during transport with an effect on day-old chicks. Probe equipment was installed in a truck of a poultry company from Spain, including a total of 66 journeys made in commercial conditions between May and November 2017. Animal-based measures collected included BW (before and after transport), mortality during transport, mortality during the first week of life, which were contrasted against a series of environmental variables including air temperature, RH, and carbon dioxide (CO 2 ) atmospheric concentration for every journey, number of day-old chicks (%) per journey, transport duration (h), zones inside the loading area (zone 1, near to the cabin; zone 2, in the central point; and zone 3, close to the back doors), height (1, top; 2, medium; and 3, bottom), mo (May to November), number of stops, type of stop during journey (farm stops and driver stops), time to start the journey, as well as other intrinsic factors of chicks (gender, breed [Ross and Cobb], breeder flock age [wk] and egg storage day). Because the database included random factors, longitudinal data, and repeated measures, a multivariate model was used to analyze the data. The results showed that chick weight loss was positively associated with journey duration and RH. No effect of environmental variables was found on mortality during transport. However, chick mortality during the first week of life was related with the percentage of day-old chicks loaded per journey and chick gender. In conclusion, owing to the environmental heterogeneity during transport and the effect of the environment on chick weight during transport and mortality at first week of life, there is an urgent need to refine the air-conditioning and ventilation systems of day-old chick transport toward a greater environmental homogeneity.