Mineral imbalance
Citrus by-products have an unbalanced Ca:P ratio that may cause milk fever in dairy cows (Bampidis et al., 2006).
Rumen parakeratosis
High levels of citrus pulp in ruminant diets can result in rumen parakeratosis, a digestive condition that has been widely reported in livestock fed high-concentrate, low-roughage rations (Arthington et al., 2002). Large amounts of volatile fatty acids, particularly butyric acid, cause rumen papillae to become enlarged and keratinized, thus restricting nutrient absorption and impairing animal performance (Brugère-Picoux, 2004).
Mycotoxins
Fresh citrus pulp can become mouldy leading to the formation of mycotoxins. The method of storage has to be correct (Bampidis et al., 2006).
Limonin
Limonin is a triterpenoid present in the seeds and skins that imparts a bitter taste to citrus pulp. If large quantities of seeds are present their limonin content may render the pulp toxic to non-ruminants, even at a level of 2.5% of their diets (Rihani, 1991; Fuller, 2004; Devendra, 1988). It has been suggested that limonin caused intestinal irritation and poor absorption of the nutriments in broilers (El Boushy et al., 2000).
Limonin should not be confounded with limonene, another terpenoid present in large quantities in citrus peels and that is responsible for the characteristic odour of citrus. Limonene is practically non-toxic to birds and mammals (EPA, 1994).
Lectins
There have been reports of a Type IV hypersensitivity reaction that caused the death from haemorragia and heart failure of several cows fed citrus pulp. This inflammatory reaction may be the result of a lectin-like hemagglutinating activity thought to be present in citrus pulp. This toxicosis could not be reproduced in sheep and rabbits (Saunders et al., 2000; Tokarnia et al., 2001).
Other natural compounds
Compounds such as tannins, saponins, phytates, oxalates and flavonoids have been identified in citrus peels but they are below the levels reported to be toxic to livestock species (Oluremi et al., 2007).
Pesticides
Contamination with pesticide residues can occur and depends on the compound, dose used, amount of rain, time between application and harvest and citrus species. In Brazil, pesticide residues in citrus pulp have decreased in the early 2000s due to a more rational application of pesticides (Oliveira et al., 2004).