日粮蛋白水平和叶酸补充方式对奶公牛营养物质消化率、氮平衡以及血液代谢产物的影响

Effects of different protein level and folic acid (FA) supplementary mode on nutrient digestibility,nitrogen balance and blood metabolites in dairy bulls

为了揭示日粮蛋白水平和叶酸补充方式对奶公牛营养物质消化率、氮平衡以及血液代谢产物的影响。试验选用8头9月龄、体重为(286.8±2.3) kg的中国荷斯坦奶公牛,随机分为4组,采用2[正常日粮(NPD)与高蛋白日粮(HPD)]×2[日粮补充3.6 mg/kg的叶酸(FA)或过瘤胃叶酸(RPFA)]因子的4×4拉丁方设计。结果显示,HPD显著提高了干物质、有机物、粗蛋白、粗脂肪、粗纤维、中性洗涤纤维和酸性洗涤纤维的消化率(P<0.05),RPFA较FA仅提高了粗脂肪的消化率(P<0.05)。采食氮、消化氮、沉积氮和沉积氮/消化氮随着日粮蛋白水平的提高而显著增加(P<0.05)。RPFA显著提高了采食氮、粪氮和沉积氮(P<0.05),降低了尿氮和尿氮/总排泄氮(P<0.05)。HPD和RPFA均提高了血清中葡萄糖、白蛋白、总蛋白和叶酸(P<0.05),降低了游离脂肪酸、乙酰乙酸和同型半胱氨酸(P<0.05)。HPD显著提高了血清中尿素氮和甘油三酯(P<0.05),而RPFA有相反的结果(P<0.05)。HPD对血清β-羟丁酸浓度无影响(P>0.05),但RPFA显著降低了其浓度(P<0.05)。结果提示,在添加叶酸的前提下日粮蛋白水平为15.02%时可提高营养物质消化率和利用率,过瘤胃叶酸较叶酸提高了蛋白质利用率。

The objective of this study was to de-termine the effects of different protein level and folic acid (FA) supplementary mode on nutrient digestibility, nitrogen balance and blood metabo-lites in dairy bulls. Eight Chinese Holstein dairy bulls with 9 mouths-of-age and (286.8± 2.3) kg of body weight were used in a replicat-ed 4×4 Latin square experiment with a 2×2 fac-torial arrangement of treatments. Normal protein [130.1 g/kg of CP (NPD)] or high protein [150.2 g/kg of CP (HPD)] diets were fed with 3.6 mg FA per kg diet DM or with 3.6 mg FA as rumen-protected fo-lic acid (RPFA) per kg diet DM. The results showed that the digestibility of dry matter, organic mat-ter, crude protein, crude fiber, neutral detergent fiber and acid detergent fiber was higher in calves fed HPD than NPD (P<0.05), but no significant difference between RPFA and FA (P<0.05). The nitro-gen intake, digestible nitrogen (DN), nitrogen retained (RN) and RN/DN increased with increasing di-etary protein levels (P<0.05). The nitrogen intake, fecal nitrogen and nitrogen retained were higher for RPFA than for FA supplementation, while urinary nitrogen (UN) and the ratio of UN to total N excret-ed (TN) was lower for RPFA than for FA supplementation (P<0.05). Serum glucose, albumin, total pro-tein and folic acid were improved by both HPD and RPFA supplementation (P<0.05), but non-esteri-fied fatty acid, acetoacetate and homocysteine decreased by both HPD and RPFA supplementation (P< 0.05). Serum urea nitrogen and triglyceride were higher for HPD than NPD (P<0.05), but lower for RP-FA than FA (P<0.05). Serum β-hydroxybutyrate was lower for RPFA than FA (P<0.05). The results indicated that nutrient digestibility and utilization were improved when dietary protein level changed from 13.01% to 15.02% in dairy calves with FA supplementation. Compared with FA supplementa-tion, nitrogen utilization was improved by RPFA supplementation.