与荷斯坦(HO)奶牛相比,棕色瑞士(BS)奶牛的牛奶和血液中的尿素浓度更高。我们检验了BS和HO奶牛在肾功能和氮排泄方面不同的假设。血,唾液,尿液,在相同的喂养和管理条件下饲养的31头多胎BS和46头HO母牛中采样了粪便。在每月DHIA对照测试日之后的不同泌乳阶段收集样品。为了测试肾小球滤过率(GFR)和尿素排泄,测定血清中肌酐和尿素的浓度,尿液,还有唾液.作为估计GFR的额外标记,我们测定了血清中的对称二甲基精氨酸(SDMA)。分析粪便的干物质含量和氮浓度。关于牛奶尿素和蛋白质浓度的数据,从每月DHIA测试日记录中获得每日产奶量。品种的影响,时间,和血液上的奇偶校验数字,唾液,尿液,粪便,和牛奶参数用GLM程序与品种进行评估,时间,和奇偶校验数作为固定效果。BS和HO之间的差异通过Tukey校正的t检验以P<0.05评估。尿素的浓度,肌酐,和血清中的SDMA,BS高于HO奶牛(P<0.01):5.46±0.19vs4.72±0.13mmol/L(尿素),105.96±2.23vs93.07±1.50mmol/l(肌酐),和16.78±0.69对13.39±0.44µg/dL(SDMA)。我们观察到BS奶牛的尿素浓度(25.8±0.7vs21.8±0.7mg/dL)和牛奶中的蛋白质含量(3.70±0.08vs3.45±0.07%)高于HO奶牛(P<0.01)。尿液和唾液中的尿素和肌酐浓度在品种之间没有差异。没有观察到BS和HO之间的差异,粪便DM,和粪便氮含量。BS和HO奶牛的干物质摄入量和体重相似(P>0.05)。尽管尿素含量较高,肌酐,与HO相比,血液中的SDMA浓度以及BS中更高的牛奶尿素含量,不同品种的尿液中各自的浓度没有差异.总之,我们的结果表明,与HO奶牛相比,BS的肾脏GFR较低,从而有助于BS奶牛中更高的血浆尿素浓度。然而,估算通过牛奶排泄的氮,尿液,粪便不能完全反映动物体内的氮代谢。
Brown Swiss (BS) cows have greater urea concentrations in milk and blood compared with Holstein (HO) cows. We tested the hypothesis that BS and HO cows differ in kidney function and nitrogen excretion. Blood, saliva, urine, and feces were sampled in 31 multiparous BS and 46 HO cows kept under identical feeding and management conditions. Samples were collected at different lactational stages after the monthly DHIA control test-day. To test the glomerular filtration rate (GFR) and urea excretion, concentrations of creatinine and urea were measured in serum, urine, and saliva. As an additional marker to estimate GFR, we determined symmetric dimethylarginine (SDMA) in serum. Feces were analyzed for dry matter content and nitrogen concentration. Data on milk urea and protein concentrations, and daily milk yield were obtained from the monthly DHIA test-day records. The effects of breed, time, and parity number on blood, saliva, urine, feces, and milk parameters were evaluated with the GLM procedure with breed, time, and parity number as fixed effects. Differences between BS and HO were assessed by the Tukey-corrected t-test at P < 0.05. Concentrations of urea, creatinine, and SDMA in serum, were greater in BS than in HO cows (P < 0.01): 5.46 ± 0.19 vs 4.72 ± 0.13 mmol/L (urea), 105.96 ± 2.23 vs 93.07 ± 1.50 mmol/l (creatinine), and 16.78 ± 0.69 vs 13.39 ± 0.44 µg/dL (SDMA). We observed a greater urea concentration in BS cows (25.8 ± 0.7 vs 21.8 ± 0.7 mg/dL) and protein content in milk (3.70 ± 0.08 vs 3.45 ± 0.07%) than in HO cows (P < 0.01). Urea and creatinine concentrations in urine and saliva did not differ among breeds. No differences between BS and HO were observed for milk yield, fecal DM, and fecal nitrogen content. Dry matter intake and body weight were similar in BS and HO cows (P > 0.05). Despite greater urea, creatinine, and SDMA concentrations in blood as well as a higher milk urea content in BS compared with HO, respective concentrations in urine did not differ between breeds. In conclusion, our results demonstrate a lower renal GFR in BS compared with HO cows, thereby contributing to the greater plasma urea concentration in BS cows. However, estimation of nitrogen excretion via milk, urine, and feces does not entirely reflect nitrogen turnover within the animal.