All vertebrates possess a daily rhythm, encompassing a comprehensive set of physiological, cognitive, and behavioral patterns that manifest throughout a 24-hour period. The aim of this study was to compare the effect of crude protein (CP) levels in the diet on the daily rhythm of urea in serum (US) and saliva in alpacas and sheep. Ten alpacas and ten sheep, adult, clinically healthy males, were used; they were maintained in natural light conditions and fed ad libitum with two levels of CP (16 and 7%). Blood and saliva samples were taken every 4 h for 48 h. A two-way ANOVA was conducted to analyze the parameters, including adjusted mean rhythm (MESOR), amplitude, and acrophase. It was found that both US and saliva urea exhibited circadian rhythms with a peak during the midday (10:59 − 12:16 h). The MESOR with low CP diets was higher (P < 0.05) in alpacas. The MESOR of urea levels in saliva was greater (P < 0.05) at the highest level of CP in the diet, with no differences between alpacas and sheep (P > 0.05). The amplitude was greater (P < 0.05) in alpacas and at the high level of CP compared to the low level of CP in the diet. Our findings reveal that both serum and saliva urea levels in alpacas and sheep follow a daily rhythm and the MESOR of US was higher in alpacas when they consume food with low CP content, and this difference disappears when CP levels are increased in the diet.

所有脊椎动物都具有每日节律，包括 24 小时内表现的一整套生理、认知和行为模式。本研究的目的是比较饮食中粗蛋白 (CP) 水平对羊驼和绵羊血清 (US) 和唾液中尿素日节律的影响。使用十只羊驼和十只绵羊，均为临床健康的成年雄性；它们被维持在自然光条件下，并随意饲喂两种水平的CP（16%和7%）。 48 小时内每 4 小时采集一次血液和唾液样本。进行双向方差分析来分析参数，包括调整平均节律（MESOR）、振幅和末期。研究发现，美国尿素和唾液尿素均表现出昼夜节律，在中午（10:59 – 12:16）达到峰值。低 CP 日粮的 羊驼MESOR 较高 ( P < 0.05)。 日粮中 CP 最高水平时，唾液中尿素水平的 MESOR 较高（P < 0.05），而羊驼和绵羊之间没有差异（ P  > 0.05）。 与日粮中低水平 CP 相比，高 CP 水平下羊驼的振幅更大（P < 0.05）。我们的研究结果表明，羊驼和绵羊的血清和唾液尿素水平均遵循每日节律，当羊驼食用低 CP 含量的食物时，US MESOR 较高，而当饮食中 CP 水平增加时，这种差异消失。