日粮不同NDF/NFC水平对周岁后荷斯坦奶牛生产性能、营养物质消化率、瘤胃发酵特征和甲烷排放的影响

本试验研究了日粮中不同中性洗涤纤维/非纤维性碳水化合物（NDF/NFC）水平对周岁后荷斯坦奶牛生产性能、营养物质消化率、瘤胃发酵特征及甲烷产量的影响，并在此基础上建立了甲烷排放预测模型，旨在获得我国生产模型下的甲烷排放规律和甲烷转化因子，为提高奶牛能量利用效率、建立国家或区域性温室气体排放清单和探索减排策略提供科学依据和支撑。将45头体况良好，平均为15月龄的荷斯坦后备奶牛随机分为3组，每组15头牛：低日粮NDF/NFC组（NDF/NFC=0.60）、中日粮NDF/NFC组（NDF/NFC=0.75）和高日粮NDF/NFC组（NDF/NFC=0.90），试验期为70 d，包括14 d的预饲期和56 d的正试期。结果表明：1）提高日粮NDF/NFC水平显著降低了奶牛的干物质采食量、有机物采食量、平均日增重、干物质和粗蛋白的表观消化率（P<0.05）；2）提高日粮NDF/NFC水平显著增加了瘤胃内总挥发性脂肪酸产量、乙酸的相对含量和乙酸/丙酸比例（P<0.05），显著降低了丙酸的相对含量（P<0.05）；3）随着日粮NDF/NFC水平的提高，瘤胃甲烷和甲烷能产量、甲烷/代谢体重、甲烷/干物质采食量、甲烷/有机物采食量、甲烷/中性洗涤纤维采食量显著提高（P<0.05）。甲烷转化因子也随着日粮NDF/NFC水平的增加而显著提高（P<0.05）；4）基于体重、采食量、营养物质含量和NDF/NFC分别建立了甲烷预测模型，其中基于干物质采食量和中性洗涤纤维采食量建立的预测模型的决定系数最高（R²=0.77）。因此，提高日粮中NDF/NFC水平可显著降低周岁后荷斯坦奶牛的生产性能、营养物质消化率和瘤胃内丙酸的相对含量，可显著提高瘤胃甲烷产量和甲烷转化因子。

Effects of dietary NDF:NFC ratio on growth performance,nutritive digestibility,ruminal fermentation characteristics and methane emissions of Holstein heifers

The present study examined the effect of different dietary neutral detergent fiber/non-fibrous carbohydrate(NDF∶NFC)levels on growth performance,nutrient digestibility,ruminal fermentation and methane(CH4)emissions of Holstein heifers.The objective was to obtain the CH4emission data and CH4conversion factor(CH4-E/gross energy intake)under the current production system,to provide scientific evidence and references to develop mitigation strategies.Forty-five 15-month-old Holstein heifers in healthy condition were selected and randomly assigned to three groups,with 15 animals in each group:low NDF∶NFC group(NDF∶NFC=0.60),medium NDF∶NFC group(NDF∶NFC=0.75),and high NDF∶NFC group(NDF∶NFC=0.90).The experiment lasted 70 d with a14 d adaptation period and 56 d measurement period.It was found that:1)increasing the dietary NDF∶NFC levels significantly decreased dry matter intake(DMI),organic matter intake(OMI),average daily gain(ADG),DM and crude protein(CP)digestibility(P<0.05).2)Increasing the dietary NDF∶NFC levels significantly increased total VFA concentration,acetate content(%)and acetate∶propionate ratio,but significantly decreased propionate content(%)(P<0.05).3)Increasing the dietary NDF∶NFC levels significantly increased enteric CH4,methane energy(CH4-E),CH4∶metabolizable body weight,CH4∶DMI,CH4∶OMI,CH4∶NDF intake(P<0.05).The CH4conversion factor significantly increased when dietary NDF∶NFC levels increased(P<0.05).4)Several prediction equations were developed using body weight,feed intake,nutrient content,or NDF∶NFC.Among these,an equation developed using DMI and NDF intake had highest R2value of 0.77.It is thus concluded that the increasing dietary NDF∶NFC decreased growth performance,nutrient digestibility,and ruminal propionate concentration,but significantly increased enteric CH4emissions and CH4conversion factors of Holstein heifers.