Aharoni, Y., Beef Cattle Section, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 1021, Ramat Yishay 30095, Israel
Dolev, A., MIGAL - Galilee Technological Center, Qiryat Shemona, PO Box 90000, Rosh Pina 12100, Israel
Henkin, Z., Beef Cattle Section, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 1021, Ramat Yishay 30095, Israel, Department of Natural Resources, Agricultural Research Organization - the Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Yehuda, Y., MIGAL - Galilee Technological Center, Qiryat Shemona, PO Box 90000, Rosh Pina 12100, Israel
Ezra, A., Beef Cattle Section, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 1021, Ramat Yishay 30095, Israel
Ungar, E.D., Department of Natural Resources, Agricultural Research Organization - the Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Shabtay, A., Beef Cattle Section, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 1021, Ramat Yishay 30095, Israel
Brosh, A., Beef Cattle Section, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 1021, Ramat Yishay 30095, Israel

The foraging behavior and energy costs of activity of 19 large-frame Beefmaster × Simford (BS) cross mature cows and 14 small-frame Baladi (BA) mature cows was determined. Cows were allocated to the same paddock of a Mediterranean pasture and were monitored during 5 seasons throughout 2006 and 2007: spring (April 2006), summer (June 2006), autumn (September 2006), winter (February 2007), and early spring (March 2007). Cows were given poultry litter (25% CP, DM basis) as supplemental feed during autumn only. The cows were fi tted for 3 to 4 d in each season with global positioning system (GPS) monitors, activity monitors attached to 1 of their hind legs, and heart rate (HR) monitors harnessed to their chests. Oxygen consumption per heart beat was determined for each cow during each season to enable conversion of the diurnal HR patterns to heat production (HP) units. All GPS data of cattle locations and activity and the HR and HP data were synchronized to produce simultaneous 5-min interval records; step length also was calculated for each record. These records provided summaries of partitioning among activities: lying down, standing, foraging, and walking without foraging as well as horizontal and vertical distances walked per day and number of steps taken per day. These attributes were analyzed using multiple regression models to relate these activities to HP and to estimate specifi c HP costs per unit of each activity. Accordingly, the daily energy costs of activity were calculated for the 2 cattle types in each season as the product of the specifi c activity and the number of units of each activity per day. The HP level of the large-frame BS cows was greater than that of the small-frame BA cows in winter and lower in spring (P < 0.001); however, the respective HP levels were much closer in summer and autumn, with BA cows having values greater by 3% than those of BS cows. The BA cows were more active than the BS cows during all seasons: they foraged for more hours per day (P < 0.001) and walked longer distances (P < 0.001). The mean specifi c costs of activity of BA cows were 20% less than those of BS cows (P < 0.001). The BA cows took longer steps during foraging and walking idle compared with BS cows despite their much smaller frame. The BA cows were more effi cient in conditions of low herbage quality whereas metabolic rate of BS cows was greater in conditions of high herbage quality. © 2013 American Society of Animal Science. All rights reserved.