The study evaluated the effect of the energy supplementation on the optimal culling age of guinea pigs (Cavia porcellus) in the Peruvian highlands. Two hundred guinea pigs of 4 weeks old were distributed in fours treatments during 13 weeks: forage ad libitum (T0), forage ad libitum plus 10 g barley grain/animal (T1), forage ad libitum plus 7 g sunflower seed/animal (T2), and forage ad libitum plus 5 g barley grain and 3.5 g sunflower seed/animal (T3). A randomized complete block design, with initial live weight defining the block, and 5 experimental units of 10 animals each, was applied. The energy supplementation improved body weight gain and feed conversion index (p<0.05), whereas the combination of sunflower seed and barley grain had an additional effect on body weight gain (T3) and the inclusion of sunflower (T2) on feed conversion index (p<0.05). The energy supplementation had no effect on production cost, benefit/cost ratio or optimal culling age.