Effects of free air carbon dioxide enrichment and drought stress on the feed value of maize silage fed to sheep at different thermal regimes

Abstract

Information about the effects of rising atmospheric CO₂ concentration and drought on the feed value of maize silage and interactions with the thermal environment during feeding is limited. A free air carbon dioxide enrichment facility was operated in a maize field to generate an elevated CO₂ concentration of 550 ppm. Drought was induced by the exclusion of precipitation in one half of all experimental plots. Plants were harvested, chopped and ensiled. In a balance experiment on sheep, the nutrient digestibility was determined for three climatic treatments (temperate, temperature humidity index (THI) 57–63; mild heat, THI 68–71; severe heat, THI 75–80). The CO₂ concentration and drought did not alter the crude nutrient content of silage dry matter (DM) or nutrient and organic matter (OM) digestibility. Drought increased the concentration of deoxynivalenol (DON, p < 0.001). The drought-associated increase of DON was reduced by CO₂ enrichment (p = 0.003). The lowest digestibility of acid detergent fibre (p = 0.024) and neutral detergent fibre (p = 0.005) was observed during the coldest climate. OM digestibility increased during mild heat (p = 0.023). This study did not indicate considerable alterations of the feed value of maize silage due to increased atmospheric CO₂ and drought. Enriched CO₂ may decrease DON contaminations during drought. The thermal environment during the balance experiment did not interact with feeding maize silage grown under elevated CO₂, but may affect cell wall and OM digestibility.

Keywords:

• carbon dioxide enrichment
• digestibility
• drought
• environmental temperature
• maize silage
• mycotoxins
• sheep

Acknowledgements

The study was supported by the Ministry for Science and Culture of Lower Saxony within the network KLIFF – climate impact and adaptation research in Lower Saxony. Furthermore, the assistance of the co-workers of the Institute of Animal Nutrition and the Experimental Station of the Friedrich-Loeffler-Institute in Braunschweig, Germany in performing experiment and analysis and the provision of FACE maize samples by the staff of the Institute of Biodiversity, Johann Heinrich von Thuenen-Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries in Braunschweig, Germany is gratefully acknowledged.