The study aimed to evaluate the excretion of purine derivatives (PDs) and nitrogen compounds (NCs) and their ratios with creatinine in supplemented Zebu heifers kept on pastures by comparing total urine collection and spot sampling. Five Nelore heifers (400 ± 15 kg) were used in a 5 × 5 Latin square design. The treatments were the amount of concentrate (220 g of crude protein/kg dry matter) offered (0, 3, 6, 9 and 12 g/kg BW). In each period, the total urine collection was performed continuously for 3 days (subsampled at intervals of 4 h, 00:00–04:00 h, 04:00–08:00 h, 08:00–12:00 h, 12:00–16:00 h, 16:00–20:00 h and 20:00–24:00 h). The spot urine samplings were performed (in each period) for 24 h (0, 4, 8, 12, 16 and 20 h). Creatinine, total urinary nitrogen (UN), urea nitrogen (UreaN), allantoin and uric acid were analysed. Creatinine excretion was 23.01 ± 0.19 mg/kg BW and was not affected by collection day, treatment or their interactions (p > 0.05). Treatments affected (p < 0.05) PD excretions, however did not affect the ratio PD:creatinine (p > 0.05). Treatments and collection time affected (p < 0.05) NC excretion, whereas the UN:creatinine and UreaN:creatinine ratios were not affected (p > 0.05). Creatinine excretion and the PD:creatinine ratios in the urine samples estimated by the total or spot sampling were not different (p > 0.05). However, sampling method affected (p < 0.05) the UN:creatinine and UreaN:creatinine (p < 0.05) ratios. Creatinine can adequately estimate urinary excretion in grazing heifers, and a single spot urine sample at any time of the day can be used to estimate PD excretion in grazing heifers. But two spot urine samples are needed for proper NC excretion estimations in grazing heifers’ urine.

中文翻译：

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使用总尿液收集或放牧小母牛的现场尿液样本估计嘌呤衍生物和氮化合物的排泄量

该研究旨在通过比较总尿液收集和现场采样来评估在牧场饲养的补充瘤牛小母牛中嘌呤衍生物 (PD) 和氮化合物 (NC) 的排泄量及其与肌酐的比率。五头 Nelore 小母牛 (400 ± 15 kg) 用于 5 × 5 拉丁方格设计。处理是提供的浓缩物量（220 克粗蛋白/千克干物质）（0、3、6、9 和 12 克/千克体重）。每个时间段连续采集3天的尿液（间隔4小时、00：00-04：00、04：00-08：00、08：00-12：00、12 :00–16:00 小时、16:00–20:00 小时和 20:00–24:00 小时）。现场尿液采样（在每个时期）进行了 24 小时（0、4、8、12、16 和 20 小时）。分析了肌酐、总尿氮 (UN)、尿素氮 (UreaN)、尿囊素和尿酸。p  > 0.05）。治疗会影响 ( p  < 0.05) PD 排泄，但不影响 PD:肌酐比率 ( p  > 0.05)。处理和收集时间影响 ( p  < 0.05) NC 排泄，而 UN:肌酐和尿素:肌酐比率不受影响 ( p  > 0.05)。通过总采样或点采样估计的尿样中肌酐排泄量和 PD:肌酐比值没有差异 ( p  > 0.05)。然而，采样方法影响（p  < 0.05）UN：肌酐和尿素N：肌酐（p < 0.05) 比率。肌酐可以充分估计放牧小母牛的尿排泄量，一天中任何时间的单点尿样均可用于估计放牧小母牛的 PD 排泄量。但是在放牧小母牛的尿液中，需要两个现场尿液样本来正确估计 NC 排泄量。