Productive, Physiological, and Environmental Implications of Reducing Crude Protein Content in Swine Diets: A Review

Abstract

Pig production is one of the most important providers of high-quality proteins and amino acids (AAs) to human nutrition. In this sector, feeding has an important economic and environmental impact. A strategy to reduce production costs and negative sustainability effects is reducing dietary crude protein (CP) contents with or without AA supplementation. This review addresses the different aspects related to this strategy, particularly the effects on growth performance and pork traits in piglets and growing and finishing pigs, as well as the physiological molecular mechanisms' underlying effects. Insight is also provided into the effects of dietary CP reduction on the productive performances of alternative pig production systems and breeding boars and sows. Finally, an overview is conducted on the effects of dietary CP reduction on ammonia, odor, and greenhouse gas emissions arising from pig production systems. Overall, CP reduction may lead to production losses, albeit they can be, to some extent, hindered by adequate AA supplementation. Losses are particularly relevant during the post-weaning phase, whereas in finishing pigs, it may bring additional benefits, such as high intramuscular fat contents in some markets or improved gut barrier function with benefits to the animals' health and welfare, as well as decreased ammonia emissions to the environment.

Keywords: amino acid supplementation; ammonia; ideal protein balance; nitrogen excretion; pig production.

Figure 1

Major effects at the productive level of a reduction from 2 to 5% dietary CP, with or without crystalline amino acid supplementation in piglets and growing and finishing pigs of lean genetic types.

Figure 2

Major effects at the productive level of a dietary CP reduction in heavy Iberian pigs produced under alternative systems in the Iberian Peninsula.

Figure 3

Major effects of a dietary CP reduction with crystalline AA supplementation in boars, and major effects of a dietary CP reduction under thermoneutral and heat stress conditions in sows. It is noteworthy to point out that for these classes of animals, the results found in the literature are very limited and often show the opposite effects.

Figure 4

Major benefits associated with a dietary CP reduction strategy at the environmental level.

Figure 5

Major effects at the productive and physiological levels of a reduction of 2–5% in dietary CP, with a response dependent on crystalline amino acid supplementation.