Impact of diets containing spineless cactus associated with lipid sources or levels of urea on physiological parameters of lambs: preliminary studies

The results obtained in experiment 2 showed that diets containing different levels of urea did not negatively affect the thermoregulation of the lambs, which is associated with the similarity between intake of DM (average of 1153.05g/day) and NDF (average of 348.02 g/day) by animals (Table 6). All values of HR can be considered above the physiological standard for sheep (Kolb, 1981). In all groups, the RR was well above the ideal, reaching approximately 112 mpm with the use of 21.9g/kg DM of urea, which corresponds to three times more than the upper limit established by Ribeiro et al. (2008) (20 to 36 mpm). Sheep use the airways as a primary mechanism for body heat dissipation, which is a good physiological indicator of heat stress (Marai et al., 2007). Similar to what was observed in the sheep from experiment 1, the RT of lambs fed different levels of urea in substitution by soybean meal remained within the normal range for the species (Robertshaw, 2006). Our results demonstrate that diets containing different lipid sources or increasing levels of urea associated with spineless cactus and Tifton85 hay as roughages did not promote changes in the main physiological responses of feedlot lambs. However, the afternoon shift, with weather conditions less favorable to thermal comfort, impairs body homeostasis of lambs fed with lipid sources combined with spineless cactus and Tifton -85 hay.