EUROPEAN GROUP ON RABBIT NUTRITION

ABSTRACT: A collaborative study was carried out by the EGRAN group in which two different Laboratories performed two assays designed to compare three methods of evaluation (direct, substitution of a basal diet or of a reference feedstuff) of the nutritional value of a fibrous ingredient (grape pulp, GP). A basal diet high in energy and protein and including 30% of alfalfa meal (AM) was progressively substituted (10, 20, and 30%) by GP in Lab 1. The AM of the basal diet was also substituted by GP (ratio AM:GP about 30:0, 20:10, 10:20, 0:30) in Lab 2. Another two diets with GP or AM as a sole ingredient were also evaluated in Lab 1 and 2, respectively, using growing rabbits for all diets. Digestibility of diets decreased linearly (P<0.001) with GP inclusion. Nutritional value of GP estimated by difference, substituting the basal diet and AM, were not different (P>0.05) and they were not significantly affected by the substitution rate, although values estimated for the lowest substitution rates had very high variation (CV>100%).  Likewise, the nutritional value obtained by regression of basal diet and AM was similar (P>0.05). Its digestible energy (DE) was 5.553 ± 0.53 and 5.27 ± 0.53  MJ/kg DM,  respectively, whereas CPd was not different from zero. The DE value of GP determined directly (7.41 MJ/kg DM) was significantly (P<0.05) higher than those obtained by the substitution method. As conclusions i) no additive nutritional values are obtained with the direct method for such imbalance ingredients, ii) substitution of AM instead of basal diet seems to have no advantage, iii) the substitution method could be applicable only with one and high substitution rate if this falls within its normal range of incorporation, but iv) using more substitution rates to estimate the nutritional value by regression is a much more reliable method.