The inclusion of ensiled citrus pulp in diets for growing pigs: Effects on voluntary intake, growth performance, gut microbiology and meat quality

Abstract

Citrus pulp was evaluated as an alternative feedstuff in diets for growing-finishing pigs. Three diets were formulated on an iso-nutrient basis to contain 0 (C), 50 (PM) or 100 (PH) g of ensiled citrus pulp per kg on a dry matter basis (DM). At 56.7 ± 7.1 kg of body weight, 72 pigs were allocated into 3 groups according to the citrus pulp level in the diet. Body weight and voluntary feed intake (VFI) were recorded on days 0, 29 and 55. Backfat thickness (BF) and loin depth (LD) were measured at P2 using ultrasounds. Faecal samples were taken directly from the rectum and cultured for Enterobacteriaceae and Lactobacillus counts. At slaughter, carcass weight, BF at gluteus medius and meat colour was recorded. Also fatty acid profile in subcutaneous fat was determined. Pigs fed citrus pulp showed a lower (P < 0.05) VFI on a DM basis and, consequently, a lower (P < 0.05) weight gain (ADG) compared to C pigs during the first 4 weeks of study. Thereafter, no differences were found between groups. At the end of the study, C pigs showed a greater level of BF at P2 than PM and PH. The inclusion of citrus pulp significantly reduced (P < 0.05) Enterobacteriaceae in faeces, not affecting Lactobacillus population. The inclusion of citrus pulp lead to no differences in BF at gluteus medius and meat colour but tended (P < 0.10) to decrease carcass yield and increase oleic acid percentage in subcutaneous fat. It was concluded that growing pigs can adapt their gastrointestinal tract to citrus pulp as a source of high-fermentable carbohydrates without detrimental effects on growth performance and meat quality, and potential benefits on gut microbiology.

Introduction

Alternative feedstuffs are nowadays becoming increasingly important in animal nutrition because of its availability at competitive prices. By-products of citrus processing are a major concern in the Valencia Community (Spain) which is a major citrus producing area. Citrus pulp is the residue generated by pressing fresh citrus fruits, mainly oranges, for juice extraction. During this process, 45 to 60% of their weight remains in the form of peel, rag and seeds. Fresh citrus pulp is characterized by high contents of moisture (greater than 800 g/kg; Martinez Pascual and Fernandez Carmona, 1980), soluble carbohydrates and pectins together with a low level of crude protein. With almost no starch, it is comparable in composition to sugar beet-pulp. Due to its composition and the perishable nature of this by-product, it ferments and sours easily generating environmental problems when stored. Animal nutrition could contribute to solving the environmental problem linked to its elimination. The use of citrus pulp in ruminant nutrition has been extensively documented, but little is known about its acceptability or nutritive value for pigs. According to O'Sullivan et al. (2003), dried citrus pulp may be included up to 50 g/kg in the diet of growing pigs; inclusion of 100 g/kg depressed pig performance.

In the present work, the potential use of this by-product in pig nutrition was studied in terms of growth performance, gut microbiology and meat quality.