Aims: To determine the effect of different levels of esterified glucomannan (EG) on detoxification and carryover of aflatoxin (AF) from feed to milk in lactating Holstein dairy cows. Study Design: The experiment was designed as a randomized block with twelve cows allocated to each treatment group. Place and Duration of Study: Department of Animal Science, Faroogh Life Sciences Research Laboratory, between July 2011 and August 2012. Methodology: Forty-eight lactating Holstein dairy cows were individually fed a similar based ration and randomly allocated to one of four levels of EG as the experimental treatments (0, 18, 27 and 36 g/cow daily of EG, named EG-0, EG-18, EG-27 and EG-36, respectively). Milk samples were collected on d 20 and 21 of experimental period to evaluate changes in milk AF concentration, milk AF secretion (milk AF concentration × milk yield); and AF transfer from feed to milk (AF secretion as a percentage of AF intake). Results: Feed intake and milk production were not affected by dietary treatments (P>0.05) and averaged 22.08 kg and 37.57 kg/d, respectively. Milk composition was also not affected (P>0.05) by addition of EG in the diet. Inclusion of EG to the diet was not effective in reducing milk aflatoxin M1 (AFM1) concentrations (P>0.05) and averaged 35, 40, 51 and 38 ng/kg for the EG-0, EG-18, EG-27 and EG-36, respectively. In addition, there was no significant difference (P>0.05) between the dietary treatments regarding AFM1 excretion and transfer of AF from feed to milk. Transfer of AF from feed to milk averaged 1.3, 1.47, 1.86 and 1.24% for the EG-0, EG-18, EG-27 and EG-36 treatments, respectively. Conclusion: Inclusion of EG up to 36 g/d (3 time more than recommended dosage) was not effective in reducing AFM1 concentrations, AF excretion, or AF transfer from feed to milk.

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