Lysine requirement for maintenance in growing pigs

Probably due to methodological problems the knowledge about the AA requirement for maintenance in pigs is rather scarce. In the present study an alternative experimental approach was applied and its underlying hypothesis was tested, whether protein retention decreases with body weight (BW), when daily lysine intake remains constant and acts as the limiting factor for protein retention, and whether this decrease reflects the increasing requirement of lysine for maintenance. If this hypothesis can be confirmed, lysine requirement for maintenance can be calculated when assuming a certain value for lysine concentration in body protein, since marginal efficiency of dietary lysine utilisation for protein retention is not affected by its level of intake (when being below the level necessary for maximum response), BW, protein retention capacity of the animal nor by energy intake. A series of N balances experiments using twelve castrated male pigs were performed at approximately 35, 55, 80, 110, and 140 kg of BW and body composition was determined by the D2O dilution technique. Two lysine intake levels were tested to prove that the animals on the lower level respond to additional lysine and, therefore, have received a lysine-limiting diet, the prerequisite for the alternative. Based on the extent of the decrease in protein retention with BW the following estimates for the maintenance lysine requirement were derived: 18 mg/kg BW, 71 mg/kg BW, 29 mg/kg fat free substance, and 121 mg/kg body protein. These estimates are higher than values reported in the literature, which might be caused by methodological differences or by the higher feed intake of the animals in the present study. © 2008 Elsevier B.V. All rights reserved.