The impact of free air carbon dioxide enrichment (FACE) on nutrient digestibility of maize grains in pigs and broiler chickens and on ruminal in sacco degradability

• No major effects on the nutrient composition of maize grains, except for sugar content.
• Digestibility of the ether extract (EE) and the metabolisable energy (ME) were significantly increased for pigs under FACE conditions.
• Enhanced the digestibility of crude protein (CP) of the diet containing FACE maize grain in broiler chickens.
• Effective degradability of crude protein (CP) and neutral detergent fiber (aNDFom) declined significantly under FACE conditions.

A rising atmospheric CO2 concentration might affect the nutritional value of feedstuffs. Only little information about the effects of elevated CO2 on C4 plants, such as maize, is known. Therefore, the present study investigated the effects of atmospheric CO2 enrichment on the nutritional value of maize grains (cv. “Romario”), which were grown at two different atmospheric CO2 concentrations (ambient CO2: 380 ppm (AMBI) and enriched CO2: 550 ppm (FACE)) in 2008. The nutrient composition of the maize grains was analyzed and two digestibility studies with pigs (trial 1) and broilers (trial 2), and an in sacco degradability study with cows (trial 3) were performed. Regarding the chemical composition of nutrients, a significant CO2 effect on sugar concentration was observed. The grain sugar concentration increased significantly under CO2 enrichment from 19.9 to 24.8 g kg−1 DM. There were no major effects of the CO2 concentration on the other analyzed nutrients and amino acids. Different results were calculated in both digestibility studies and in the in sacco experiment. The digestibility of the ether extract (EE), organic matter (OM) and the metabolisable energy (ME) for pigs were significantly increased for diet maize grown under FACE conditions. In broiler chickens, the digestibility of crude protein (CP) of the diet containing maize grain cultivated under enriched atmospheric CO2 concentration was significantly increased from 912 to 927 g kg−1 as well as EE, which rose from 914 to 924 g kg−1. The degradability CP and neutral detergent fiber (aNDFom) in the in sacco degradability study were significantly influenced by the CO2 treatment. In both cases, the effective degradability declined significantly from about 730 to 619 g kg−1 (CP) and from 865 to 617 g kg−1 (aNDFom) under FACE conditions at a passage rate of 0.05 h−1. It is concluded that the content of crude nutrients of maize grain cultivated under elevated CO2 did not change, but the digestibility of some nutrients was significantly increased in trials with pigs and broiler chickens and the CP and aNDFom in sacco degradability was significantly decreased.