Prediction of the nutritional value of European compound feeds for rabbits by chemical components and in vitro analysis

Chemical composition and in vitro analyses were used to predict the nutritional value of 164 experimental rabbit diets evaluated in six European Laboratories under standardised conditions. The equations were mainly developed by stepwise regression analysis with over two third of the samples (111) used as calibration set. The other third (53) was used as validation set, and a study of the residues was undertaken to calculate the error of validation. Twenty three different equations have been proposed to predict the nutritional value (mainly gross energy digestibility, GEd; and digestible energy, DE) of rabbit diets, as a function of the vailable variables. Acid detergent fibre (ADFom) was the chemical variable most closely related to GEd and DE (R2 = 0.49 and 0.43, respectively, RSD = 0.033 and 0.62, for GEd and DE, respectively), but the in vitro DM digestibility (DMdinv) predicted the energy value with greater accuracy (R2 = 0.7, 0.52, for GEd and DE, respectively) and lower standard error (RSD = 0.025, 0.58 for GEd and DE, respectively). The latter equations were improved (R2 = 0.81, 0.74 for GEd and DE, respectively) when ether extract (EE) and Lignin (sa)were included. The use of additive equations that predict the DE from the main constituents that supply energy (protein, ether extract and carbohydrates) did not increase the precision, nor decrease the validation error respect to the simplest ones. Digestible Energy was predicted with a similar accuracy and validation errors than GEd. Crude protein digestibility (CPd) was better predicted from chemical analysis (Lignin (sa), R2 = 0.49) than for DMdinv. The further inclusion of CP slightly increased its coefficient of determination (0.53). The error of validation was relatively low (0.050 as average) and of the same magnitude than the RSD of the equations

European ring-test on the chemical analyses of total dietary fibre and soluble fibre of compound diets and raw materials for rabbits

Due to the role of soluble fibre (SF) on the digestive physiology and gut health of post-weaning rabbits and to the lack of reference methods for SF determination, in the framework of the harmonization activity on rabbit science methodologies carried out by EGRAN (European Group on Rabbit Nutrition), a collaborative study was achieved on the determination of total dietary fibre (TDF), aNDF corrected for protein and ash (aNDFcorr) and SF calculated as the difference between TDF and aNDFcorr. Five EGRAN laboratories analysed nine samples: four compound diets and five raw materials (alfalfa meal, wheat bran, grape marc, sunflower meal, sugarbeet pulp) with different levels of fibre fractions and SF. Each sample was analysed 3 runs for TDF and aNDFcorr. TDF was analysed according to the AOAC Method 991.43 using the kit and the procedure of Megazyme\uae. TDF averaged 48.2% DM, with one laboratory having higher values (49.3% vs 47.9%; P<0.001). The TDF values varied among samples (P<0.001), from about 40% DM for diets to 60% DM for grape marc and sugarbeet pulp. Repeatability (SR=0.95% DM) and reproducibility of TDF (SL=1.68% DM) were good with a low coefficient of variation among laboratory: CVL= 3.9%. The aNDFcorr (mean 37.1% DM) significantly differed from laboratories that used Ankom system (36.4% DM) to laboratories that used Fibertech equipment (38.3% DM). The differences among laboratories due to the equipment and to the corrections for ash and protein explained the poorer repeatability and reproducibility of aNDFcorr determination, with CVL=6.6%. SF values differed (P<0.001) among laboratories (from 9.6% to 12.0% DM) and samples (from 4.0% DM of wheat bran to 8-11% DM of diets and alfalfa meal to 24.3% DM of sugarbeet pulp). The among-laboratory variability of SF was higher (SL=2.97% DM; CVL=26.8%), due to the variability of both TDF and aNDFcorr analyses. In conclusion, TDF analysis was characterized by good repeatability and reproducibility, but it was less reproducible in case of raw materials with high SF levels. The among laboratory variation increased with aNDFcorr, because of the differences in analytical equipment and the procedure for protein and ash corrections. Finally SF reproducibility appeared rather good for complete diets and raw materials with low or medium concentration (SF 4-10% DM), but it was affected by the analytical errors of both TDF and aNDFcorr and needs a better harmonization