Zou Songyan, Ji Shoukun, Xu Hongjian, Wang Mingya, Li Beibei, Shen Yizhao, Li Yan, Gao Yanxia, Li Jianguo, Cao Yufeng, Li Qiufeng
College of Animal Science and Technology, Hebei Agricultural University, Baoding 071000, China.
College of Animal Medicine, Hebei Agricultural University, Baoding 071000, China.
Animals (Basel). 2023 Feb 25;13(5):843. doi: 10.3390/ani13050843.
The aim of this study was to investigate the effect of low-protein diets supplemented with rumen-protected lysine (RPLys) and methionine (RPMet) on growth performance, rumen fermentation, blood biochemical parameters, nitrogen metabolism, and gene expression related to N metabolism in the liver of Holstein bulls. Thirty-six healthy and disease-free Holstein bulls with a similar body weight (BW) (424 ± 15 kg, 13 months old) were selected. According to their BW, they were randomly divided into three groups with 12 bulls in each group in a completely randomized design. The control group (D1) was fed with a high-protein basal diet (CP13%), while bulls in two low-protein groups were supplied a diet with 11% crude protein and RPLys 34 g/d·head + RPMet 2 g/d·head (low protein with low RPAA, T2) or RPLys 55 g/d·head + RPMet 9 g/d·head (low protein with high RPAA, T3). At the end of the experiment, the feces and urine of dairy bulls were collected for three consecutive days. Blood and rumen fluid were collected before morning feeding, and liver samples were collected after slaughtering. The results showed that the average daily gain (ADG) of bulls in the T3 group was higher than those in D1 ( < 0.05). Compared with D1, a significantly higher nitrogen utilization rate ( < 0.05) and serum IGF-1 content ( < 0.05) were observed in both T2 and T3 groups; however, blood urea nitrogen (BUN) content was significantly lower in the T2 and T3 groups ( < 0.05). The content of acetic acid in the rumen of the T3 group was significantly higher than that of the D1 group. No significant differences were observed among the different groups ( > 0.05) in relation to the alpha diversity. Compared with D1, the relative abundance of Christensenellaceae_R-7_group in T3 was higher ( < 0.05), while that of Prevotellaceae _YAB2003_group and Succinivibrio were lower ( < 0.05). Compared with D1 and T2 group, the T3 group showed an expression of messenger ribonucleic acid (mRNA) that is associated with (CPS-1, ASS1, OTC, ARG) and (N-AGS, S6K1, eIF4B, mTORC1) in liver; moreover, the T3 group was significantly enhanced ( < 0.05). Overall, our results indicated that low dietary protein (11%) levels added with RPAA (RPLys 55 g/d +RPMet 9 g/d) can benefit the growth performance of Holstein bulls by reducing nitrogen excretion and enhancing nitrogen efficiency in the liver.
本研究旨在探讨补充瘤胃保护赖氨酸（RPLys）和蛋氨酸（RPMet）的低蛋白日粮对荷斯坦公牛生长性能、瘤胃发酵、血液生化参数、氮代谢以及肝脏中与氮代谢相关基因表达的影响。选取36头体重相近（体重424±15 kg，13月龄）、健康无病的荷斯坦公牛。根据体重，将它们完全随机分为三组，每组12头。对照组（D1）饲喂高蛋白基础日粮（粗蛋白含量13%），而两个低蛋白组的公牛分别饲喂粗蛋白含量为11%且添加34 g/d·头RPLys + 2 g/d·头RPMet的日粮（低蛋白低RPAA，T2）或55 g/d·头RPLys + 9 g/d·头RPMet的日粮（低蛋白高RPAA，T3）。实验结束时，连续三天收集奶牛公牛的粪便和尿液。在晨饲前采集血液和瘤胃液，屠宰后采集肝脏样本。结果表明，T3组公牛的平均日增重（ADG）高于D1组（P<0.05）。与D1组相比，T2组和T3组的氮利用率（P<0.05）和血清IGF-1含量（P<0.05）均显著更高；然而，T2组和T3组的血尿素氮（BUN）含量显著更低（P<0.05）。T3组瘤胃中乙酸含量显著高于D1组。不同组间的α多样性无显著差异（P>0.05）。与D1组相比，T3组中Christensenellaceae_R-7_group的相对丰度更高（P<0.05），而Prevotellaceae_YAB2003_group和琥珀酸弧菌属的相对丰度更低（P<0.05）。与D1组和T2组相比，T3组肝脏中与（CPS-1、ASS1、OTC、ARG）和（N-AGS、S6K1、eIF4B、mTORC1）相关的信使核糖核酸（mRNA）表达；此外，T3组显著增强（P<0.05）。总体而言，我们的结果表明，添加RPAA（55 g/d RPLys + 9 g/d RPMet）的低日粮蛋白水平（11%）可通过减少氮排泄和提高肝脏中的氮效率来促进荷斯坦公牛的生长性能。
