The Impact of Drought, Heat and Elevated Carbon Dioxide Levels on Feed Grain Quality for Poultry Production

Climate change has wide-reaching consequences for agriculture by altering both the yield and nutritional composition of grains. This poses a significant challenge for the poultry industry which relies on large quantities of high-quality feed grains to support meat and egg production. The existing literature shows that elevated atmospheric carbon dioxide concentrations (eCO₂), heat and drought overall reduce grain yield and quality. However, these results are inconsistent, with some studies reporting small or large decreases and others even indicating potential improvements. These variations may occur because many studies only investigate one climate factor at a time, without considering interactions between factors. Additionally, most studies investigate just one grain type, rather than comparing grains and their morphophysiological differences. The present review offers a novel approach by investigating how eCO₂, heat and drought interactively affect both the yield and nutritional composition of four key animal feed grains: wheat (<i>Triticum aestivum</i> L.), barley (<i>Hordeum vulgare</i> L.), maize (<i>Zea mays</i> L.) and sorghum (<i>Sorghum bicolour</i> L. Moench). The photosynthetic pathway is a key determinant of a plant’s response to climate factors, so this review compares grains with both C₃ photosynthesis (wheat and barley) and C₄ photosynthesis (maize and sorghum). The present review found that eCO₂ may promote starch synthesis in C₃ grains of wheat and barley, thereby improving grain yield but diluting protein, lipid, vitamin and mineral concentrations. This potential yield improvement is further counteracted by heat and drought which limit the photosynthetic rate. Unlike wheat and barley, C₄ photosynthesis is not CO₂-limited, so neither the yield nor the nutritional quality of maize and sorghum are significantly affected by eCO₂. On the other hand, heat stress and drought reduce photosynthesis in maize and sorghum and may offer minimal increases in nutrient concentrations. This review highlights that while eCO₂ may increase the yield of wheat and barley grains, this effect (i) dilutes nutrient concentration, (ii) is counteracted by heat and drought, and (iii) does not benefit C₄ grains maize and sorghum. An additional novel insight is offered by discussing how the impacts of climate change on animal feed production may be mitigated using alternative crop management practices, plant breeding, feed processing and enzyme supplementation.