Glucosinolates in animal nutrition: A review

Glucosinolates (Gls) are secondary plant metabolites that occur in all Brassica-originated feeds and fodders. Content and composition of Gls vary due to plant species, agronomic practices and climatic conditions. The Gls content is generally higher in rapeseed meal (RSM) varieties grown under tropical environment than those occur in temperate regions. The RSM from Indian sub-continent contain primarily 3-butenyl, 2-propenyl and 4-pentenyl glucosinolates. But 2-propenyl glucosinolate accounts more than 0.95 of their total glucosinolates present in RSM of European and other temperate countries, and did not contain 4-pentenyl glucosinolates. Depending on the pH, cofactors and Gls content and composition of RSM, major metabolites of glucosinolates are thiocyanates (SCN), isothiocyanates (ITC), nitriles, 5-vinyl-2-oxazolidinethione (VOT) and 5-vinyl-1,3-oxyzolodine-2-thione (5-VOT). Apart from total glucosinolate (TGls) content SCN, nitriles and VOT estimates are the chief attribute of RSM quality as these are produced upon hydrolysis of Gls following the processing of RSM. Major deleterious effects of glucosinolates ingestion in animals are reduced palatability, decreased growth and production. Progoitrin and epi-progoitrin impair palatability at a level between 2.3 and 4.65 μmol g−1 diet, while at higher levels feed intake decreases. Nitriles are known to affect liver and kidney functions. The thiocyanates interfere with iodine availability, whereas VOT is responsible for the morphological and physiological changes of thyroid. Difference in Gls profile among the RSM induces varying levels of glucosinolates metabolites in animal tissues. Rapeseed meal feeding did not impair quality traits of carcass and increased unsaturated fatty acids (C22:2 and trans C18:1) content in carcass and milk fat. Ruminants are less sensitive to dietary glucosinolates. Pigs are more severely affected by dietary glucosinolate compared to rabbit, poultry and fish. The tolerance level (μmol g−1 diet) of TGls in ruminants, pig, rabbits, poultry and fish is 1.5–4.22, 0.78, 7.0, 5.4 and 3.6 μmol, respectively. Water extraction, heat and CuSO4 treatments were found suitable for RSM quality improvement. Iodine supplementation in the diet of pigs (1.0 mg kg−1) and ruminants (500 mg I each kg RSM) seems promising because of economic and easiness compared to other treatments. Therefore, a desired amount of RSM can be used for animal feed formulation adopting a suitable technology to minimize or remove Gls-related deleterious effects on animals.