Stable isotope analysis of ¹³C and ¹⁵N has been widely used to provide information regarding short- or long-term animal dietary composition as affected by changes in land or ecological system use. In complex mixed-crop−livestock systems, rangeland biomass, crop residues, and feedstuff contribute to livestock diets with high seasonal variations. Particularly in the Limpopo province, South Africa, livestock feed supply varies considerably throughout the year leading to regular feed gaps. Hence, to estimate livestock diet composition in relation to these variations, we analyzed the stable isotopes of C and N of tail hair and feces samples across free-ranging beef cattle in distinct agroecological zones (AEZs) and farm types. Here, farm types were structured according to mixed-crop−livestock farms and livestock-only farms. We found that farm types did not influence the $\delta$¹³C of feces and hair (P > 0.05), but AEZ had a strong effect on $\delta$¹³C patterns (P < 0.01). The contribution of C₃-C₄ plants in the diet varied considerably across farm types and AEZ (P < 0.01). The $\delta$¹⁵N values indicated nutritional stress, probably due to low protein concentrations in feed (e.g., rangeland biomass, crop residues) irrespective of AEZ and farm types. In general, cattle exposed to arid conditions (drier AEZ) had significantly decreased $\delta$¹³C values and increased $\delta$¹⁵N values that could potentially be linked to feed gaps. Moreover, the results from the present study indicate that $\delta$¹³C of feces and hair samples are more meaningful predictors of cattle diet than $\delta$¹⁵N as affected by different farm practices. Therefore, stable isotope analyses potentially have an important role in helping improve the understanding of seasonal shifts in livestock diet intake in diverse production systems.

¹³ C 和¹⁵ N稳定同位素分析已广泛用于提供有关受土地或生态系统利用变化影响的短期或长期动物膳食成分的信息。在复杂的农作物-牲畜混合系统中，牧场生物量、农作物残留物和饲料导致牲畜饮食具有很大的季节性变化。特别是在南非林波波省，牲畜饲料供应全年变化很大，导致经常出现饲料缺口。因此，为了估计与这些变化相关的牲畜饮食成分，我们分析了不同农业生态区 (AEZ) 和农场类型的自由放养肉牛的尾毛和粪便样本的 C 和 N 稳定同位素。在这里，农场类型是根据混合作物-畜牧农场和纯畜牧农场来构建的。我们发现农场类型并不影响$\delta$¹³ C 粪便和毛发 ( P > 0.05)，但 AEZ 对$\delta$^{13 个}C 模式（P < 0.01）。_{C 3} -C ₄植物在日粮中的贡献因农场类型和 AEZ 的不同而有很大差异（ P < 0.01）。这$\delta$¹⁵ N 值表明营养压力，可能是由于饲料中蛋白质浓度低（例如牧场生物量、农作物残留物），与 AEZ 和农场类型无关。一般来说，暴露在干旱条件下（较干燥的 AEZ）的牛的数量显着减少$\delta$¹³ C 值增加$\delta$¹⁵ N 值可能与饲料缺口相关。此外，本研究的结果表明$\delta$^{粪便和毛发样本的13} C 比牛的饮食更有意义的预测因子$\delta$¹⁵ N 受不同农场做法的影响。因此，稳定同位素分析可能在帮助提高对不同生产系统中牲畜饮食摄入季节性变化的理解方面发挥重要作用。