Stypinski J D, Kononoff P J, Weiss W P
Department of Animal Science, University of Nebraska-Lincoln, NE 68503.
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691.
JDS Commun. 2023 Apr 28;4(4):251-254. doi: 10.3168/jdsc.2022-0345. eCollection 2023 Jul.
Starch and NDF are usually assumed to contain the same concentration of gross energy (GE), but NDF is more variable in chemical composition and varies more in the extent of digestion. The variable chemical composition of NDF may have direct implications on dairy nutrition models that predict dietary GE and use this estimate for also predicting digestible energy. For example, when NDF is enriched in lignin and protein, the concentration of GE would increase, whereas NDF enriched in ash would have the opposite effect. Current nutritional models, such as the NASEM (2021) and CNCPS (6.55), assume a GE coefficient of 4.20 Mcal/kg for NDF. This study aimed to determine the heat of combustion of NDF and to consider if it is a contributing factor to the variance in digestible energy. To do so, NDF residues were isolated from 9 feed and 8 fecal samples and then combusted. Approximately 0.20 g of NDF residues from 16 feeds (corn silage, n = 2; grass hay, n = 2; alfalfa hay, n = 2; wheat straw, n = 1; cottonseed hulls, n = 1; soyhulls, n = 1; distillers dried grains with solubles, n = 1; and total mixed ration, n = 6) and 34 fecal samples were collected. A bomb calorimeter (Parr 6400 Calorimeter, Parr Instrument Company) was used to determine concentration of GE in each NDF residue sample. The GE concentration of feed NDF was observed to be 4.03 ± 0.245 Mcal/kg, which was similar to that of fecal NDF (3.94 ± 0.245 Mcal/kg). The lack of difference between feed and fecal NDF GE implies that digested NDF is of a similar GE concentration as total feed NDF and that current nutritional models are validated in their current approach in predicting digestible energy from NDF. However, our observed estimate of GE in NDF is lower than what is assumed and across feed types varied from 3.85 to 4.19 Mcal/kg.
淀粉和中性洗涤纤维（NDF）通常被认为含有相同浓度的总能（GE），但NDF的化学成分更具变异性，消化程度的变化也更大。NDF化学成分的变异性可能会对预测日粮GE并将该估计值用于预测消化能的奶牛营养模型产生直接影响。例如，当NDF富含木质素和蛋白质时，GE浓度会增加，而富含灰分的NDF则会产生相反的效果。当前的营养模型，如美国国家科学院、工程院和医学院（NASEM，2021）以及康奈尔净碳水化合物和蛋白质体系（CNCPS，6.55），假定NDF的GE系数为4.20兆卡/千克。本研究旨在测定NDF的燃烧热，并探讨其是否是消化能变异的一个影响因素。为此，从9份饲料和8份粪便样本中分离出NDF残渣，然后进行燃烧。收集了来自16种饲料（玉米青贮，n = 2；禾本科干草，n = 2；苜蓿干草，n = 2；小麦秸秆，n = 1；棉籽壳，n = 1；大豆壳，n = 1；带可溶物的干酒糟，n = 1；以及全混合日粮，n = 6）和34份粪便样本中约0.20克的NDF残渣。使用弹式量热仪（帕尔6400量热仪，帕尔仪器公司）测定每个NDF残渣样本中的GE浓度。观察到饲料NDF的GE浓度为4.03±0.245兆卡/千克，与粪便NDF的GE浓度（3.94±0.245兆卡/千克）相似。饲料和粪便NDF的GE之间没有差异，这意味着消化后的NDF与总饲料NDF的GE浓度相似，并且当前的营养模型在从NDF预测消化能的当前方法中得到了验证。然而，我们观察到的NDF中GE的估计值低于假定值，并且在不同饲料类型中，其范围为3.85至4.19兆卡/千克。
