Organic diets and physical activity: Research experience using a rat model

Total energy expenditure or heat production is comprised of basal metabolic rate, thermic effect of food, and physical activity. Physical activity is the most variable and easily altered component of total heat production. Physical activity is influenced by a number of biological parameters i.e. diet, genetics, age, and gender. The diet components of the macro as well as micronutrients and other components (secondary metabolites) associated with a diet could contribute to the well being of the animal and cause variation in physical activity. In order to investigate physical activity as a parameter to differentiate diets based on conventional or organic grown carrots the total heat production and physical activity was measured in a rat model. The experimental diets were formulated to meet the NRC requirements for rats by mixing 40% of freeze dried carrots with an Altromin chow diet. The carrots were from a 2-year field study. The carrots were grown by three different cultivation strategies: one conventional (C) and two organic systems (OA, organic using animal manure; and OB, organic using cover crops). The diets were given to weaned female GKMol rats, in groups of five rats per diet and given their assigned diet, for approx. 2.5 months. Throughout the experimental period the rats were monitored and weighed each week. The rat’s heat production and physical activity was measured with two open-air circuit respiration chambers, and measurement was done on a group of 5 rats. In the chamber the rats were placed in individual cages. The activity was measured using both passive infrared detectors and with video recording. There was not surprisingly lower physical activity level of rats during the day. Being night-active animals, rats are usually resting during the day-time