Prickly pear pulp in the feeding of livestock ruminants: preliminary investigation

In Sicily, the current increasing cultivation of Opuntia ficus-indica (L.) Mill. corresponds to a availability of prickly pears pulp (PPP) that residues from fruits processing for juice extraction, comprised of peel, pulp and seeds. This investigation aim to evaluate the nutritional traits of PPP for ruminants feeding, and the effect of potassium metabisulfite (PMB) as a natural stabilizer to limit initial rapid PPP fermentation. The by-product, collected in August, included 28% of peel and pulp (PP) and 72% of seeds on dry matter (DM), with seeds higher in ether extract (EE) and NDF and comparable for DM and crude protein (CP) (DM 35.5, 35.9 and 35.6%; EE 6.5, 3.6 and 8.5% DM; CP 6.5, 6.0 and 6.7% DM; NDF 62.0, 41.5 and 73.3% DM, for PPP, PP and seeds). For PPP, the net energy for lactation was 1.1 Mcal/kg DM, total polyphenols were 2.71 mg GAE/g DM, the DPPH (IC50) resulted 65.6 mg DM/ml, and the reducing power (EC50) 109.4 mg DM/ml. The PPP showed a total microbial load of 1.7 x 105 CFU/g, mainly due to mesophilic cocci lactic acid bacteria (1.4 x 106 CFU/g), responsible of sugar fermentation, and hosted a certain presence of coliforms (1.2 x 105 CFU/g) derived from the environment, while Escherichia coli, Listeria monocytogenes and Salmonella spp. were not detected. Four heaps of fresh PPP, each of 20 kg, were placed on the ground, treated with different PMB doses (0, 50, 100 and 150 g/100 kg of PPP for T0, T1, T2 and T3), and covered by a breathable plastic sheet, simulating the storage technique in farms. The PMB doses were established to have a very low risk to reach the maximum amount recommended by WHO for human consumers (0.7 mg/kg of body weight). The initial pH of PPP (5.0) decreased more slowly in the treated heaps, reaching after 9 days values of 3.80, 4.05, 4.21 and 4.23 with T0, T1, T2 and T3. Similarly, in the treated heaps, the sugar content decreased more slowly from day 1 (133.4 g/kg) to day 7 (8.8, 9.1, 9.5 and 9.7 g/kg with T0, T1, T2 and T3), suggesting a certain efficiency of higher PMB doses to slower the initial fermentation. Based on these first results, the PPP appears an interesting by-product to be used as feeding source able to increase the environmental and economic sustainability of ruminants livestock. Appropriate researches are necessary to set up methods to preserve the PPP safety during storage, and evaluate its potential antioxidant properties that can be beneficial to livestock animals and consumers of their products.