Effects of processing methods on the digestibility and palatability of ... cessing form (chopped, ground or meal forms; Experiment 2) and the effects of increasing.
Animal Feed Science and Technology 162 (2010) 135–143
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Effects of processing methods on the digestibility and palatability of cassava root in growing pigs C. Régnier, B. Bocage, H. Archimède, D. Renaudeau ∗ INRA UR143 Unité de Recherches Zootechniques F-97170 Petit Bourg, Guadeloupe, French West Indies, France
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Article history: Received 14 October 2009 Received in revised form 9 September 2010 Accepted 14 September 2010
Keywords: Cassava root Hydrocyanic acid Digestibility Palatability Creole pig
a b s t r a c t Four experiments were carried out to evaluate the effects of processing methods on the digestibility and palatability of cassava roots (CR) in growing pigs. Fresh CR were ground with a vegetable biomass chopper (ground CR) or manually chopped with a slicing tool into thin chips (chopped CR). An electric grinder with a 3 mm diameter screen was used to make CR meal from dried ground CR obtained after a 6-h drying period (meal-6 h). The ground, chopped and meal forms were chosen because they are the main forms used for feeding pigs in such geographical areas. In Experiment 1, changes in hydrocyanic acid (HCN) and dry matter (DM) contents in chopped and ground CR were measured during a 24-h drying period in a solar dryer. The minimum drying times required to reach the minimum HCN content in ground and chopped CR were 3 and 6 h, respectively. The second and third experiments were designed to determine the effects of the processing form (chopped, ground or meal forms; Experiment 2) and the effects of increasing incorporation rates of ground CR (Experiment 3) on the coefficient of total tract apparent digestibility (CTTAD) of nutrients and energy in the experimental diets. In Experiment 2, a total of six pigs were studied in a 3 × 3 Latin square design. Each pig was fed alternately with one of the three experimental cassava forms, being offered 400 g/kg DM of CR products and 600 g/kg DM of a control corn soya bean meal (CSBM) diet. In Experiment 3, four pigs were studied in a 4 × 4 Latin square design and the dietary treatment included a gradual increase in ground CR from 0 to 600 g/kg of DM offered in the CSBM diet. In Experiment 2, it was found that the energy CTTAD of the experimental diet was not affected by the cassava form (chopped, ground or meal) (P>0.05), and averaged 0.927. In Experiment 3, the CTTAD of organic matter and energy linearly increased (P BpT, HCN = a. Values of a, b and BpT were determined using the NLIN procedure in the statistical package SAS (2008). The CTTAD values of DM, OM, CP, ash, starch and energy were calculated for each pig involved in Experiments 2 and 3. The digestible energy content (DE) was estimated as the difference between the measured gross energy (GE) and the estimated energy loss in faeces (Noblet, personal communication). The metabolizable energy content (ME) of the diet was calculated as the difference between the DE and energy loss in urine estimated from the N loss (g/d) according to the equation in Noblet and Le Goff (2001). The amount of nitrogen retained was taken as the difference between intake and losses in faeces and urine. The results obtained for Experiments 2 and 3 were analysed independently using analysis of variance (SAS, 2008) including the effects of diet, replicate and animal. The means were compared according to the PDIFF option, using the Tukey test for contrasts. In Experiment 2, the digestive utilisation of CR products was calculated according to the difference method (Noblet and Shi, 1994). Assuming that the energy, starch and crude protein digestibility of the control diet remained constant in the experimental diets, the CTTAD of the energy and dietary chemical fractions of the CR products in Experiment 2 were calculated from the incorporation rate in feed and the CTTAD of control and mixed (control + CR products) diets in Experiment 2. For this, we assumed that the CTTAD of the control diet was similar in Experiments 2 and 3. For Experiment 3, linear regressions between CTTAD measured in the experimental diets and the incorporation rate of ground cassava roots were calculated. 3. Results 3.1. Experiment 1: the effects of drying time and water loss on HCN content In fresh material (t0), the DM of CR was 230 g/kg and the HCN content was lower in ground than in chopped CR (0.66 vs. 1.03 g/kg DM, respectively; P BpT, HCN = a + b x BpT For ground CR, a = 0.66 g/kg DM, b = -152 mg/kg DM/h, and Bpt = 2.9 h. For chopped CR, a =1.03 g/kg DM, b = -107 mg/kg DM/h, and Bpt = 5.7 h.
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Drying time (hours) Fig. 1. Effect of drying time on the hydrocyanic acid content (HCN) in ground (䊉) and chopped () cassava root (CR), (Experiment 1). Each point is the average of two values. A broken line relationship was used to predict the reduction of HCN content while increasing drying time. The break point time (BpT) is the minimum time required to reduce HCN content. The HCN initial content of cassava root was 1027 mg/kg DM.
CR (−129 mg of HCN/kg DM/h on average; P>0.05; Fig. 1). A time of 2.9 h was required to obtain ground CR with a minimum value of HCN (0.22 g/kg DM; Figs. 1 and 2). The corresponding values for the chopped CR were 5.7 h and 0.42 g/kg DM, respectively. Before the breakpoint DM content, each percentage increase in DM led to a reduction in HCN content by 51 and 12 mg/kg DM in ground and chopped CR, respectively (Fig. 2). The minimum HCN content was obtained at 420 and 780 g/kg of DM in chopped and ground CR, respectively. According to the results of the first experiment, 6 h of drying was chosen to minimise the risk of toxicity from HCN and to compare the nutrient and energy digestibility of ground and chopped CR. 3.2. Experiments 2 and 3: chemical composition and nutritive value In comparison to the control diet, the CR products were characterised by their low nitrogen and NDF contents and a high starch content (Table 1). The chemical composition within the CR products was very similar except for NDF and HCN concentrations. The NDF content was slightly higher in ground and meal CR forms than in chopped CR. The HCN content was 14-fold higher in chopped than in meal CR (25 vs. 367 mg/kg, respectively), whereas an intermediate value was reported for the ground CR (212 mg/kg). The resulting average body weights (BW) and total DM contents offered were similar for all dietary treatments in Experiment 2 (57.5 kg and 169 g DM/d/kg BW0.60 , respectively; Table 2). In contrast to the other treatments, feed refusals were collected from pigs fed the chopped CR diet. Analysis of the refusals showed that they were essentially composed of chopped CR. As a consequence, the actual rate of incorporation of chopped CR was lower than planned (29 vs. 40%). The CTTAD did not differ (P>0.05) between the dietary treatments except for energy. The energy CTTAD of chopped-6 h and meal-6 h CR diets was higher than that of the ground-6 h CR diet (average of 0.903 vs. 0.896, respectively; P=0.036). In the same way, the DE and ME values of chopped-6 h and meal-6 h CR diets were higher than those of the ground-6 h CR diet (16.1 and 16.0 vs. 15.9, and 15.6 and 15.5 vs.15.4 MJ/kg DM, respectively; P
