Israeli researchers studied grazing behavior, diet intake, and energy cost of activity in two types of cows. Large crossbred Beefmaster-Simmental-Hereford cows averaged 1278 lb and small Israeli-native Saladi cows averaged 599 lb. The location of the experiment has a moderate Mediterranean climate averaging 22 in/yr precipitation, with almost none typically occurring from May to October. Cows of both types were grazed together, stocked at either 1.4 acres/cow or 2.8 acres/cow. Cows were supplemented with free-choice 25% CP dry poultry litter in autumn. GPS monitors attached to cows allowed measurement of activity, heart rate, and oxygen consumption.

The small cows had higher forage consumption per unit of metabolic weight (Wt 3/4) and they selected higher-quality forage in spring. Also, small cows averaged grazing 1.63 hours/day more and covered 35 percent more ground per day (2.74 miles versus 2.03 miles). Both types of cows grazed less and covered less ground as forage quality declined from spring to summer. When supplement was provided in autumn, grazing time and movement increased; this was attributed to increased forage digestibility due to the nitrogen supplied in the supplement. The authors noted that energy costs of physiological processes are similar in animals of differing size when based on metabolic weight. However, energy cost of movement is related to total weight, not metabolic weight. Therefore, movement requires relatively less energy for smaller animals. In conclusion, the authors determined that the smaller cows had advantages in efficiency of feed utilization and lower relative energy required for movement. (J. Animal Sci. 87:2719)

Source: Dr. Stephen Hammack, Professor & Extension Beef Cattle Specialist Emeritus, Texas A&M University

AgriLife Research and Extension