Forage crop farming is shown as the most important way of continuous and safe forage production. Clover and vetch are the most used forage plants. In this research clover (Medicago sativa) and vetch (Vicia sativa) plants were planted in large pots (48x18x18cm) containing peat: perlite mixture (3:1). The seeds were kept in distilled water for 3 hours before planting and swelling was ensured. After the peat perlite mixture prepared in pots was watered sufficiently with distilled water and then seeds were planted. 1000 ppm heavy metal stock solutions have been prepared for lead nitrate Pb(NO3)2, copper nitrate Cu(NO3)2.3H2O, and cadmium nitrate (CdNO3)2.4H2O. Prepared heavy metal solutions were given to the plants at once, with irrigation water, in 300 mL for each pot. Total protein amount and peroxidase activity were examined by spectrophotometrically 72 hours after the heavy metal application. Three different heavy metals applications to the forage plants, have been showed different physiological reactions in these plants. These reactions have been measured by comparing control group of plants. According to research results, it was determined that the maximum increase in the total protein amount in M. sativa compared with the control group was 100 ppm applied lead. The maximum increase in the total protein amount in V. sativa compared with the control group was 30 ppm applied cadmium, respectively. The increase in peroxidase activity has been determined in M. sativa and V. sativa plants compared with the control groups were 30 ppm applied cadmium. As a result of our research, it was determined that cadmium has been found to be more effective than lead and copper for stimulation of plant defense system.