The current study aimed to investigate the effects of replacing alfalfa hay with potato vines hay (PVH) and potato vines silage (PVS) on growth performance, digestibility and blood metabolites of fattening lambs. For this, twenty-four fattening lambs were assigned randomly to one of four dietary treatments. Treatments included: 1) basal diet without potato vines (CTRL); 2, 3) replacing 50 and 100% of alfalfa in the basal diet with PVH (PVH50, PVH100, respectively); and 4) replacing 50% of alfalfa with PVS (PVS50). The diets were formulated to be iso-energetic and iso-nitrogenous and were fed ad-libitum to lambs during 70 days of performance period. Blood samples, taken on d 30 and 70, were analyzed for biochemical and hematological parameters. At the end of performance period, lambs were transferred into metabolic crates and the digestibility of the diets were evaluated during 7 d fecal collection, following a 14-d adaptation period. Metabolizable energy (ME) and organic matter digestibility (OMD) of PVH and PVS as well as ruminal digestibility and fermentation of the diets were determined in vitro using gas production technique. Organic matter (%), CP (%), NDF (%), OMD (%) and ME (MJ/kg) contents were 79.2, 14.7, 45.1, 72.3, 8.74; 89.9, 16.1, 43, 58.8, 7.74; and 90.4, 14.5, 48, 67.2, 9.5 for PVH, PVS and alfalfa, respectively. Replacing alfalfa with PVH and PVS had no effect on the growth performance of lambs (P > 0.05). However, total volatile fatty acids (TVFA) concentration was affected by the treatments (P < 0.01), with the lowest value observed with PVH100. There was no significant treatment effect on nutrients digestibility except for CP, which tended to increase with PVH100. In vitro results showed no treatment effect on ruminal digestibility (P > 0.05). Partitioning factor (PF) tended to increase with PVH and PVS containing diets (P = 0.09). However, there was a treatment effect on the gas produced after 24 h incubation (GP24) and TVFA (P < 0.05), with thei
