Raw and extruded field beans (Vicia faba var. minor) as alternative protein sources in heavy lamb diets

Abstract

The possible risk connected to GMO use in animal breeding leads to reconsider animal production processes with special reference to the use of alternative protein sources able to replace soy bean, whose production accounts for about 60% GMO. The aim of the trial was to evaluate the possibility to replace soy bean with field bean for the heavy lamb diet and to study the effect of the processing treatment (extrusion) on the productive performances, the energy and protein metabolism parameters and on the quanti-qualitative characteristics of the carcass and the meat.Twenty-four male Gentile di Puglia lambs were divided, when 42 days old, into three homogeneous groups according to live weight (12,0 ± 0,5 kg) and assigned to the following feeding treatments: a) soy bean (control); b) raw field bean; c) extruded field bean. Food consumptions and live weights were recorded weekly in order to calculate the daily weight gain and the feed conversion index; blood samples were collected every 21 days and plasma concentration of glucose, triglycerides, cholesterol (energy metabolism), and BUN, total proteins, protein electrophoresis (protein metabolism) were measured. At 90 days of age, after 12 hours of fasting, lambs were slaughtered and the dressing percentage was calculated. After refrigeration at 4 °C for 24 hours, the carcasses were sectioned into cuts, and the pelvic limb and lumbar region were dissected into tissue components (lean, fat and bone) (ASPA, 1991). The pH values were measured at slaughtering and 24 h later on the Longissimus dorsi (Ld) and Semimembranosus (Sm) muscles. Meat colour features (L, a, b) were assessed by using a spectrophotometer (Hunter Lab, D65/10° illuminant). Data were analyzed by ANOVA using the GLM procedure of SAS and means were compared using the Student’s t test.The use of raw field bean showed better daily weight gain (250 g) when compared to c) group (220 g) and, especially, a) group (200 g, P<0.05). The blood indexes characterizing the energetic and protein metabolism were affected by lambs’ age but not by their feeding treatment. The pH of both the muscles, Ld and Sm, were not influenced by the feeding treatment at the slaughtering time, while 24 hours later the pH value of the Ld was significantly higher in the control group (6,10 ± 0,18) when compared to c) group (5.71 ± 0.02; P<0.01) and b) group (5.78±0,05; P<0.05). No statistical differences with regards to the incidence of the different cuts of the half carcass were detected among treatments. As for the tissue components of the pelvic limb cut, the percentage of lean in the control group (62.44±1.39) was lightly lower compared to the field bean groups, either extruded (63,28±2,15) or raw (64.44±0.67 %). The percentage of fat was lower for the extruded field bean treatment (9.03±0.78) with respect to that recorded with the use of soy bean (11.23 ± 0.60; P<0.05) or of raw field bean (12.83±0.78; P<0.01). With concern to the colorimetric characteristics of the Ld muscle, the index of redness was greater in the group fed with raw field bean when compared to control (10.39±0,42 vs 9.33±0.29; P<0.05). On the other hand, the brightness (37.90±1.44) and the yellowness (7.81±0.47) of the Sm muscle were significantly lower (P<0.05) in b) group when compared to a) and c) groups.It is concluded that field bean may represent a valid alternative to soy bean as a protein feed for growing lambs in so-called “organic” animal production systems where transgenic soy is banned.