Under heat-load conditions eating and digestion may cause an increased heat load if they coincide with the hottest part of the day. The studies were designed to assess the effect of time of feeding on the heat production (HP) pattern during the day and on performance and efficiency. The presented data are derived from three summer studies, of about 90 days each year, located at two feedlots. One lot was unshaded; in the other shade was provided by a 3- to 4-m-high roof, covering about onethird of the yard. Holstein and beef-breed fattening calves, and growing beef heifers were used. In each feedlot each year animals were separated by breed, gender and age, and into two treatments, day and night fed. The day-fed animals received most of the feed during the day; the nightfed animals, during the night. Intake and efficiency were measured on group basis. During the years we used 417 animals, separated into 11 groups in each treatment. Heart rate (HR) and skin temperature were recorded throughout the day by data loggers harnessed to the chest behind the forelegs. In one year, HP throughout the day was calculated by multiplying HR by the measured HP per heartbeat. The night-fed cattle manifested the lowest HP during the hottest hours of the day, but the full-day HP was reduced only a little by night feeding. Overall, the 3-year study showed that time of feeding did not affect growth rates: 1.259 and 1.266 kg/day for the day- and night-fed, respectively (SED 0.048, P<0.89). Night feeding significantly reduced DM intake, from 7.325 to 6.693 kg/day (SED 0.246, P<0.021), and tended to increase feed efficiency (gain per unit intake), from 177 to 194 (g gain per kg DM intake; SED 8.9, P<0.083).