14 Challenges and opportunities for formulating low-protein diets for maintaining growth and N-retention of weanling and growing-finishing pigs

Abstract

Abstract For more than two decades, numerous studies have been conducted evaluating the effects of lowering CP level in pig diets. It is now accepted that lowering dietary CP level and adding crystalline amino acids (CAA) improves N utilization and consequently reduces N excretion. Increased availability of CAA such as Lys, Thr, Met, Trp, Val (Ile, Arg and His) allows nutritionists to further reduce dietary CP level while meeting pigs’ AA requirements more closely. However, pig performance was sometimes compromised when the dietary CP level was reduced more than 4 percentage units and adding high inclusion levels of CAA. An increase in backfat thickness was also sometimes reported when feeding finishing pigs with low CP diets. The potential reasons for such inconsistent results are due to the deficiency of the next limiting AA (typically Val and Ile), inaccurate feed mixing and insufficient amount of non-essential AA (NEAA) in the low CP diets. Formulating low CP diets on similar energy content as for the high CP diets on ME basis sometimes led to a greater backfat thickness in finishing pigs which was mainly due to increased energy utilization of pigs fed low CP diets coupled with the excess energy being stored as carcass fat. Based on the results of these experiments, optimal growth performance, carcass quality and N retention of pigs can be maintained when low CP diets are balanced for adequate levels of both essential AA and NEAA on the standardized ileal digestible basis combined with formulating on NE basis. Research suggests that keeping a maximum total Lys:CP ratio of 7.4% could overcome deficiency of NEAA in the low CP diets. Based on published N-balance studies, 1 percent unit dietary CP reduction results on average 9% reduction in N excretion in pigs which is an effective approach to become more sustainable pork production.