Abstract

Stable isotopes are an important tool to assess livestock diet in binary mixtures of C3-C4 forages. However, the use of stable isotopes to trace livestock diet using tropical arboreal legumes has been limited. The objective of this study was to evaluate the use of ¹³C stable isotopes to identify the proportions of grass (C4) and legume in sheep diet, when consuming various inclusion levels. We evaluated models correlating faecal δ¹³C to diet δ¹³C and inferred which model can better predict the different proportions of grass or legume consumed by sheep. Thirty male lambs (17 ± 1.3 kg) were used, and the experiment was set up in a randomised complete block design with body weight being the criteria for blocking. Treatments included various inclusion levels of Sabiá (Mimosa caesalpiniifolia Benth) in signalgrass (Urochloa decumbens Stapf) hay (100:0, 75:25, 50:50, 25:75 e 0:100%). Total faecal production and in vivo digestibility were calculated, as well as δ¹³C of diet and faecal samples. Sabia diet (100%) showed the greatest overall intake, and the lowest faecal production was observed when forages were fed alone, both for signalgrass or sabia hays, with 234 and 245 g dry matter animal⁻¹ d⁻¹. The models used within this study estimated with high accuracy the grass-legume proportions within the diets of sheep (R²=0.97). Our results indicate that using additional coefficients (digestibility, discrimination) did not increase the accuracy of the models, since using only isotopes from faeces was sufficient to predict the contribution of C3 or C4 species in the diet.

• Highlights

• Stable isotopes are an efficient tool to trace back dietary sources in binary mixtures of C₃-C₄ forages.

• Faecal samples are accurate to use to trace back dietary changes using stable isotopes.

• Addition of digestibility and isotope discrimination coefficients did not improve prediction models.

摘要

稳定同位素是评估C3-C4饲草二元混合物中牲畜饮食的重要工具。然而，使用稳定的同位素来追踪热带树木类豆科动物的家畜饮食受到了限制。这项研究的目的是评估使用¹³ C稳定同位素来确定食用各种含量的绵羊饲料中草（C4）和豆类的比例。我们评估模型相关粪便δ ¹³ C到饮食δ ¹³C并推断出哪个模型可以更好地预测绵羊消耗的草或豆类的不同比例。使用了三十只雄性羔羊（17±1.3公斤），并以随机完整块体设计进行了实验，体重是封闭的标准。处理方法包括在信号草（Urochloa decumbens Stapf）干草（100：0、75：25、50：50、25 ：75 e 0：100％）中的Sabiá（含羞草含羞草）的不同包涵水平。总粪便生产和体内消化率计算，以及δ ¹³饮食和粪便样本C。撒比亚饮食（100％）显示出最大的总摄入量，而当单独饲喂草料时，无论是信号草还是sa草，分别有234和245 g干物质动物^-1 d ^-1，粪便产量最低。本研究中使用的模型以高准确性估算了绵羊饮食中的草-豆科植物比例（R ² = 0.97）。我们的结果表明，使用其他系数（消化率，判别力）不会提高模型的准确性，因为仅使用粪便中的同位素就足以预测饮食中C3或C4物种的贡献。

• 强调

• 稳定同位素是追踪C ₃ -C ₄饲料的二元混合物中饮食来源的有效工具。

• 粪便样品可以准确地追溯使用稳定同位素的饮食变化。

• 消化率和同位素鉴别系数的增加并没有改善预测模型。