Rabbit Feces as Feed for Ruminants and as an Energy Source

SIMPLE SUMMARY: This paper investigates the potential use of rabbit feces as a source of nutrition for ruminants and as an energy source. Feeding rabbit feces to ruminants or biogas production with rabbit manure may reduce the competition between human food and animal feed, provide a partial solution to some environment problems, and reduce treatment and disposal cost of manure. The in vitro rumen digestibility of rabbit feces was experimentally measured to assess its value as a feed for ruminants. In parallel, in order to extract the information about its potential nutritive and energetic value, the whole and partial relationships between the nutrient constituents of the rabbit feces and/or crop forages were investigated by chemometric analysis and also validated by near-infrared spectroscopy (NIRS). The results of this work indicated that rabbit feces has potential value as a ruminant feed and for biogas production. ABSTRACT: There are prospects for using novel feeds from various sources to provide ruminants with alternative sources of protein and energy such as by-products, and animal wastes. Rabbit feces are a concentrated source of fiber and could have commercial potential both as input biomass in anaerobic processes for biogas production, as well as a fibrous source for ruminal degradation. The aims of this work were to assess the potential as ruminant feeding and as biogas production of rabbit feces, in comparison with 12 crops. The chemical composition and the potential and experimental in vitro true digestibility (IVTD) and neutral detergent fiber digestibility (NDFD) of 148 feces samples were determined by using chemical methods, Daisy system digestibility and/or NIRS predictions. The average biomethane potential (BMP) was 286 ± 10 l(CH4)/kg SV with −4% vs. the crops average. Milk forage unit (milk FU), IVTD and NDFD of feces were 0.54 ± 0.06 milk FU/kg DM, 74% ± 3% and 50% ± 5%, respectively, with comparisons of −19%, −11% and −24% vs. the crops average. Reconstruction of the potential values based on the chemical constituents but using the crop partial least square model well agreed with the NIRS calibrations and cross-validation. In a global NIRS calibration of the feces and crops the relative predicted deviation for IVTD, NDFD and milk FU were 3.1, 2.9 and 2.6, respectively, and only 1.5 for BMP. Running the Daisy system for rabbit feces in rumen fluid gave some inconsistencies, weakened the functional relationships, and appeared not to be correlated with the potential values of IVTD and NDFD. Nevertheless, the energetic potential of feces appears to be similar to some conventional crops at different degrees of maturity. Thus we conclude that rabbit feces has potential value as a ruminant feed and for biogas production.