Effects of Replacing Extruded Maize by Dried Citrus Pulp in a Mixed Diet on Ruminal Fermentation, Methane Production, and Microbial Populations in Rusitec Fermenters

SIMPLE SUMMARY: Citrus pulp is the main by-product obtained from citrus processing. The high-moisture content of this by-product makes it rapidly perishable, its accumulation can cause environmental problems, and it causes high disposal costs for citrus processing factories. Therefore, alternative uses for citrus pulp are necessary, its use in ruminant feeding being one of the most feasible ones. In this study, we assessed the effects of replacing extruded maize in a diet for dairy sheep (20% of diet) by dried citrus pulp using an in vitro technique (Rusitec fermenters). Results showed some positive effects of citrus pulp on diet degradability and in vitro fermentation parameters. The growth of ruminal microbes and bacterial diversity were essentially unaffected. Our results indicate that maize in dairy sheep diets can be totally replaced by dried citrus pulp without negatively affecting ruminal fermentation. The use of citrus pulp would reduce the amount of human-edible ingredients used in the diet of dairy sheep. ABSTRACT: Citrus pulp is a highly abundant by-product of the citrus industry. The aim of this study was to assess the effects of replacing extruded maize (EM; 20% of total diet) by dried citrus pulp (DCP; 20%) in a mixed diet on rumen fermentation and microbial populations in Rusitec fermenters. The two diets contained 50% alfalfa hay and 50% concentrate, and the same protein level. Four Rusitec fermenters were used in a cross-over design with two 13-d incubation runs. After 7-d of diet adaptation, diet disappearance, fermentation parameters, microbial growth, and microbial populations were assessed. Fermenters receiving the DCP showed greater pH values and fiber disappearance (p < 0.001) and lower methane production (p = 0.03) than those fed EM. Replacing EM by DCP caused an increase in the proportions of propionate and butyrate (p < 0.001) and a decrease in acetate (p = 0.04). Microbial growth, bacterial diversity, and the quantity of bacteria and protozoa DNA were not affected by the diet, but the relative abundances of fungi and archaea were greater (p < 0.03) in solid and liquid phases of DCP fermenters, respectively. Results indicate that DCP can substitute EM, promoting a more efficient ruminal fermentation.