Grazing Ecology Research Group, Federal University of Rio Grande Do Sul, Porto Alegre, RS, Brazil.
State Foundation of Agricultural Research, Rua Gonçalves Dias, 570, Bairro Menino Deus, Porto Alegre, RS, Brazil.
Sci Total Environ. 2023 Apr 15;869:161695. doi: 10.1016/j.scitotenv.2023.161695. Epub 2023 Jan 21.
Forage nutrient contents are an important factor explaining the dry matter intake (DMI), average daily gain (ADG), and methane emissions (CH) of ruminants fed indoors. However, for grazing animals, the forage nutrient contents might be limited in explaining such response variables. We aimed to verify the explanatory power of forage nutrient contents and sward structure on daily intake, performance, and CH emissions by sheep and beef cattle grazing different grassland types in southern Brazil. We analyzed data from five grazing trials using sheep and beef cattle grazing on Italian ryegrass (Lolium multiflorum), mixed Italian ryegrass and black oat (Lolium multiflorum + Avena strigosa), pearl millet (Pennisetum americanum), and multispecies native grassland. We used mixed models, including the forage nutrient contents [crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF)], sward structure (sward height and herbage mass) and their interactions, as fixed effects and trial, season, methodologies, animal species, grassland type, and paddock, as random effects. The model for DMI (kg DM/LW) had an adjusted coefficient of determination (R) of 71.6 %, where 11.3, 23.1, and 37.2 % of the R were explained by the forage nutrient contents, sward structure, and their interaction, respectively. The ADG (kg/LW) model presented an R of 74.2 %, with 12.5 % explained by forage nutrient contents, 29.3 % by sward structure, and 32.4 % by their interaction. The daily CH emission (g/LW) model had a lower adjusted coefficient of determination (R = 47.6 %), with 16.8 % explained by forage nutrient contents and 30.8 % explained by sward structure, but no effect of the interaction. Our results show that in grazing ecosystems, the forage nutrient contents explain a small fraction, and the greater explanatory power for DMI, ADG, and CH emissions models is related to sward structure descriptors, such as sward height and herbage mass. Moreover, the interaction between these variables explains most of the variation. In conclusion, forage nutrient contents and sward structure have different influences on DMI, ADG, and CH emissions by grazing ruminants. Because of its relevance to daily CH emissions, offering an optimal sward structure to grazing animals is a major climate-smart strategy to improve animal production and mitigate CH emissions in pastoral ecosystems.
对于室内饲养的反刍动物，饲料养分含量是解释其干物质采食量（DMI）、平均日增重（ADG）和甲烷排放（CH）的重要因素。然而，对于放牧动物，饲料养分含量可能在解释这些反应变量方面具有局限性。我们旨在验证饲料养分含量和草丛结构对巴西南部不同草地类型放牧绵羊和肉牛的日采食量、性能和 CH 排放的解释能力。我们使用绵羊和肉牛放牧意大利黑麦草（Lolium multiflorum）、混合意大利黑麦草和黑燕麦（Lolium multiflorum + Avena strigosa）、珍珠粟（Pennisetum americanum）和多物种本地草地的 5 个放牧试验的数据进行分析。我们使用混合模型，包括饲料养分含量[粗蛋白（CP）、中性洗涤纤维（NDF）和酸性洗涤纤维（ADF）]、草丛结构（草丛高度和牧草量）及其相互作用，作为固定效应，试验、季节、方法、动物种类、草地类型和围场作为随机效应。DMI（kg DM/LW）模型的调整决定系数（R）为 71.6%，其中饲料养分含量、草丛结构及其相互作用分别解释了 11.3%、23.1%和 37.2%的 R。ADG（kg/LW）模型的 R 为 74.2%，其中饲料养分含量解释了 12.5%，草丛结构解释了 29.3%，相互作用解释了 32.4%。每日 CH 排放（g/LW）模型的调整决定系数（R）较低，为 47.6%，其中饲料养分含量解释了 16.8%，草丛结构解释了 30.8%，但相互作用没有影响。我们的结果表明，在放牧生态系统中，饲料养分含量仅能解释一小部分，而 DMI、ADG 和 CH 排放模型的更大解释能力与草丛结构描述符（如草丛高度和牧草量）有关。此外，这些变量之间的相互作用解释了大部分变化。总之，饲料养分含量和草丛结构对放牧反刍动物的 DMI、ADG 和 CH 排放有不同的影响。由于其与每日 CH 排放的相关性，为放牧动物提供最佳的草丛结构是改善动物生产和减轻放牧生态系统 CH 排放的主要气候智能策略。
