Haemocyte count, phenoloxidase activity, agglutinin levels, total protein content, bacterial clearance efficiency, resistance to the pathogen Aeromonas hydrophila and nitrite stress were measured in the giant freshwater intermoult subadult prawn Macrobrachium rosenbergii (15–20 g) which had been fed diets containing bovine lactoferrin (Lf) at 50, 100, 200 mg kg−1 feed for 7 or 14 days. M. rosenbergii fed a diet containing 100 mg Lf kg−1 diet for 7 days showed significant (P < 0.05) increase in total protein levels, agglutination titres against bacteria A. hydrophila and rabbit RBC, phenoloxidase activity, bacterial clearance (as observed through reduced number of circulating bacteria) as well as survival against A. hydrophila challenge. Increased bacterial clearance was also noticed in prawns fed Lf at 50 or 200 mg kg−1 for 14 days compared to control. Feeding of Lf at 50 mg kg−1 diet for 7 or 14 days was able to enhance only PO activity and reduce percent mortality against A. hydrophila challenge compared to its control. Total haemocyte count was higher in the lowest dose of Lf feeding, i.e. 50 mg kg−1 for 7 days. However, there was no significant alteration in the differential haemocyte population with respect to graded levels of Lf feeding for 7 or 14 days. A notable reduction in mortality percent after 120 h of nitrite stress was observed in prawn fed Lf at 100 mg kg−1 diet for 14 days. On the contrary, feeding of the highest dose of Lf, i.e. 200 mg kg−1 diet for 14 days failed to stimulate most of the innate immune parameters or reduce the percent mortality against A. hydrophila challenge or nitrite stress. It is therefore concluded that administration of Lf in the diet at 100 mg kg−1 for 7 days could enhance the immune ability of M. rosenbergii and increase its resistance to A. hydrophila infection or nitrite stress.