Advances, Implications, and Limitations of Low-Crude-Protein Diets in Pig Production

SIMPLE SUMMARY: Currently, five crystalline essential amino acids (lysine, methionine, threonine, tryptophan, and valine) are generally used, allowing animal nutritionists to formulate diets with low crude protein levels. Moreover, isoleucine may also be used depending on its economic value and the specific feeding program. Experimentally, it has been shown that further reduced crude protein levels can be achieved by supplemental histidine, leucine, and phenylalanine to the diets. However, decreasing the dietary crude protein level while maintaining optimal ratios of amino acids has shown contradictory effects on pigs’ growth performance. Due to the divergence in the literature and the importance for practical formulation strategies in the swine industry, a literature review and a meta-analysis were performed to estimate the minimum crude protein level that would not compromise pig performance. Based on the present review, there is a minimum crude protein level after which the growth performance of pigs can be compromised, even though diets are balanced for all essential amino acids. Considering average daily gain and the gain-to-feed ratio, respectively, these levels were estimated to be 18.4% and 18.3% crude protein for nursery, 16.1% and 16.3% crude protein for growing, and 11.6% and 11.4% crude protein for finishing pigs. ABSTRACT: Currently, five crystalline essential amino acids (Lys, Met, Thr, Trp, and Val) are generally used, allowing formulation of low-crude-protein (CP) diets. Moreover, Ile may also be used depending on its economic value and the specific feeding program. Experimentally, it has been shown that further reduced CP levels can be achieved by supplemental His, Leu, and Phe to the diets. However, decreasing the dietary CP level while maintaining optimal ratios of amino acids has shown contradictory effects on pigs’ growth performance. Due to the divergence in the literature and the importance for practical formulation strategies in the swine industry, a literature review and a meta-analysis were performed to estimate the minimum CP level that would not compromise pig performance. Based on the present review, there is a minimum CP level after which the growth performance of pigs can be compromised, even though diets are balanced for essential amino acids. Considering average daily gain and gain to feed, respectively, these levels were estimated to be 18.4% CP (95% confidence interval [CI]: 16.3 to 18.4) and 18.3% CP (95% CI: 17.4 to 19.2) for nursery, 16.1% CP (95% CI: 16.0 to 16.2) and 16.3% CP (95% CI: 14.5 to 18.0) for growing, and 11.6% CP (95% CI: 10.8 to 12.3) and 11.4% CP (95% CI: 10.3 to 12.5) for finishing pigs.