Hydration capacity: A new criterion for feed formulation

Twenty-four raw materials, harvested or produced in 2013 and commonly used in animal feed, were used to measure their hydration capacities through both water-holding capacity (WHC, g H2O/g DM after 24h of water addition) and swelling capacity (SC, mL H2O/g DM during 60 min after water addition, every 5 min during the first 30 min and then every 10 min). The raw materials were provided in the form of whole seeds (F1 class; n=8), flour/mash/hulls (F2 class, n=8) or pellets (F3 class, n=9). Hydration capacities were measured for unprocessed material and also after grinding of whole seeds (1, 3, 5 or 8 mm grid). The raw materials were analysed for fibre content to study the relation with WHC and SC. Moreover, WHC and SC were measured on twenty-eight compound pelleted feeds containing some of the raw materials studied in the present experiment, harvested or produced in the same year (i.e. 2013; Experimental feeds; n=8) or in an earlier year (i.e. <2013; Reference feeds; n=20) to evaluate additivity and predictability of these criteria. WHC and SC at 60 min (T60) varied greatly among the raw materials (2.88 +/- 1.74g H2O/g DM and 2.61 +/- 2.37 mL H2O/g DM, respectively; P<0.001) and are weakly correlated (R-2 = 0.52; P<0.001). They are thus two complementary measurements interesting in feed formulation. The physical form of the raw materials at the moment of delivery had a significant effect on WHC (0.97, 4.92 and 3.65 g H2O/g DM in the F1, F2 and F3 classes, respectively; P<0.001). Grinding the seeds had a significant effect on WHC and SC values (P<0.001). WHC and SC at T60 were moderately correlated with the fibre content: neutral detergent fibre (aNDF), acid detergent fibre (ADF), acid detergent lignin (ADL), hemicellulose and cellulose content (R-2<0.40 and P<0.01 the same for every fibre fraction). In the eight Experimental feeds, the correlation between calculated SC and measured SC at T60 was low (R-2=0.38; P=0.104). Conversely, the correlation between calculated WHC and measured WHC was high (R-2=0.89 and R-2=0.81; in the Experimental and the Reference feeds, respectively; P<0.001) and the mean difference between the predicted WHC and the measured WHC was moderate (9.7% and 10.6%, respectively for Experimental and Reference feeds), but could reach high values (>15%), especially when measured WHC was high. In conclusion, hydration capacity could be considered as additive, however, the theoretical values of pelleted compound feeds should be supported by real measurements. (C) 2015 Elsevier B.V. All rights reserved.