Semi-solid fermentation of nopal (Opuntia spp) for use as an animal protein supplement

In order to mitigate the severe shortage of forage and the high cost of protein sources during the winter drought in northern Mexico, new technology aimed at enriching the protein content of “nopal” (Opuntia spp) was developed. This perennial crop is highly appreciated as a forage supplement in drought conditions due to its high water content (80-90 %), although its low protein content (4-6 %) limits its nutritional value. The technology is based on semi-solid fermentation of 1-year-old spineless cladodes as substrate by using Saccharomyces cerevisiae (1 %) as yeast and adding urea (1 %) and ammonium sulfate (0.1 %) as protein sources. Fermentation occurs under aerobic conditions at a temperature of 25 ± 3 °C and acid pH of 4.35 ± 0.04 during a 10-hour process with 8 motion intervals, namely 45-minute motions and 20-minute rests. Treatments were statistically analyzed using the SAS program (9.1)/GLM procedure and Tukey’s multiple comparison test in a completely randomized design with three replicates. Results showed a significant increase in the crude protein content of fermented nopal (33.52 %) as compared to the control (7.08 %), as well as in the metabolizable energy (2.64 and 2.31 Mcal∙kg-1, respectively). As a result of fermentation, non-fibrous carbohydrates were reduced significantly (55.03 vs 25.77 % for the control and fermented nopal, respectively). Dry matter showed no significant effect (8.0 % average). Crude protein obtained in fermented nopal (30 %) is higher than that reported for alfalfa (25.8 %), but it is lower when compared on a dry matter basis (8 vs 30 % for nopal and alfalfa, respectively). However, in terms of water consumption and yield, nopal is superior to alfalfa. Later tests indicated that when used as a forage supplement in feeding bovines (both for milk and meat purposes) as well as sheep and goats, fermented nopal improved the body condition and increased their weight as compared to conventional diets.