Consequences of Increases in Ambient Temperature and Effect of Climate Type on Digestibility of Forages by Ruminants: A Meta-Analysis in Relation to Global Warming

SIMPLE SUMMARY: This work assessed how the digestion of feeds by cud-chewing animals (ruminants) is affected by animal and feed factors, ambient temperature (AT), and climatic region. The motive for this study was to simulate how forage quality and digestibility would respond under future climate change scenarios. This work allows for predictions to be made on the possible impacts of AT on the digestibility of feeds (viz. roughages, grains, leaves, stems, fruits, and concentrate formulations) consumed by ruminants. This would help farmers to plan and implement strategies for improving feed quality and to align feeding management to ensure improved growth response of ruminant livestock. Increasing AT reduced digestibility parameters consequent upon higher lignification of plant material. The amount of feed that can be potentially digested in a ruminants’ stomach (potential degradability (PD) were highest for concentrates and mixed diets compared to roughages. Potential degradability was lowest for studies carried out in tropical and arid climates compared to cold and temperate climates. Animals fed on diets classified as browse had similar PD compared to those fed on non-browses. Ensilaged feeds had similar PD compared to non-silages. A 1 °C increase in ambient temperature decreased PD by 0.55%, while the fibre content of feeds was projected to increase by approximately 0.4%. ABSTRACT: This meta-analysis evaluated the effects of ruminant feeding type, ambient temperature (AT), and climatic region on the rumen digestibility of feeds. A dataset on nylon bag degradability parameters bearing the chemical composition of roughages, grains, leaves, stems, fruits, concentrates and diets given to animals, climate type, and AT were compiled. Data were analysed using mixed model regression and simple linear regression methodologies. Negative correlations between AT and degradability parameters were observed. Potential degradability (PD) and slowly degradable fraction (‘b’) were higher for concentrates and mixed diets compared to roughages. Intermediate feeders had slower rates of degradation (‘c’) compared to grazers. Potential degradability was highest for studies carried out in cold and temperate climates compared to tropical and arid climates. A 1 °C increase in AT decreased PD by 0.39% (roughages), 0.76% (concentrates), and 2.41% (mixed diets), with an overall decrease of 0.55% for all feed types. The “b” fraction decreased by 0.1% (roughages), 1.1% (concentrates), 2.27% (mixed diets), and 0.35% (all feed types) for every 1 °C increase in AT. Increasing AT by 1 °C increased the neutral detergent fibre content of feeds by 0.4%. In conclusion, increases in AT increased the neutral detergent fibre content of feeds, lowering PD, “b”, and “c” of dry matter in the rumen.