Technical note: A proposed method to determine the extent of degradation of a feed in the rumen from the degradation profile obtained with the in vitro gas production technique using feces as the inoculum

A method is proposed to determine the extent of degradation in the rumen involving a two-stage mathematical modeling process. In the first stage, a statistical model shifts (or maps) the gas accumulation profile obtained using a fecal inoculum to a ruminal gas profile. Then, a kinetic model determines the extent of degradation in the rumen from the shifted profile. The kinetic model is presented as a generalized mathematical function, allowing any one of a number of alternative equation forms to be selected. This method might allow the gas production technique to become an approach for determining extent of degradation in the rumen, decreasing the need for surgically modified animals while still maintaining the link with the animal. Further research is needed before the proposed methodology can be used as a standard method across a range of feeds.     

瘤胃混合微生物对稻糠、玉米麸、麦麸饲料中植酸磷降解特性的比较研究

采用短期人工瘤胃发酵技术,研究瘤胃混合微生物对糠麸类饲料中植酸磷的降解作用。试验采集3头健康泌乳期荷斯坦奶牛瘤胃液,以不同来源稻糠、玉米麸、麦麸饲料为底物,测定厌氧发酵3、12、24、48和72 h饲料植酸磷的消失率。结果表明:1)糠麸类饲料植酸磷消失率均随发酵时间的延长而增加,并且在发酵至24 h时,植酸磷消失率趋于90%以上。2)不同来源的同种糠麸类饲料间植酸磷的潜在降解率和降解速率明显不同。3)3种糠麸类饲料比较发现,麦麸饲料的植酸磷潜在降解率可达到100%(P<0.000 1),而玉米麸(95.58%)与稻糠(96.82%)饲料间差异不显著(P>0.05),植酸磷降解速率呈现为稻糠>玉米麸>麦麸(P<0.000 1)。由此可见,瘤胃混合微生物能很好地降解富含植酸磷的糠麸类饲料,且降解作用在不同饲料间存在一定的差异。     

In situ disappearance of neutral detergent insoluble nitrogen from alfalfa and eastern gamagrass at three maturities.

In situ digestion kinetics of neutral detergent insoluble nitrogen (NDIN) from alfalfa (Medicago sativa L.) harvested at one-tenth bloom and eastern gamagrass (Tripsacum dactyloides L.) harvested at the boot (GGB), anthesis (GGA), and physiological maturity (GGM) stages of growth were determined with nonlinear regression techniques. Whole-plant tissue and associated leaf and stem fractions were incubated in the ventral rumen simultaneously. On a wholeplant basis, potential extents of degradation were particularly high (> or =904 g/kg NDIN) for GGB and GGA, relative to those of GGM and alfalfa (772 and 658 g/kg NDIN, respectively). For all plant parts, degradation rates of NDIN were faster (P<.05) for alfalfa than for all gamagrass forages. Degradation rate of NDIN did not differ (P>.05) across maturities for any gamagrass tissue type. These results indicate 1) that phenological development and lignification do not limit the rate of NDIN degradation in gamagrass forages but do markedly limit the potential extent of NDIN availability and 2) that most of the NDIN in these forages is potentially available in the rumen and can contribute to the ruminal N supply. Our secondary objective was to compare estimates of N escaping ruminal degradation that were determined on the basis of NDIN degradation kinetics (NDIN method) with those determined traditionally, on the basis of total residual N. The NDIN method mathematically eliminates all neutral detergent soluble N from consideration as part of the pool of dietary N potentially escaping the rumen intact. Estimates of rumen escape nitrogen determined on the basis of degradation rates of NDIN were consistently less than corresponding estimates that were determined on the basis of total residual N. When ruminal escape N that was determined with the NDIN method was regressed on corresponding estimates with the total residual N method, the slopes of the regression lines were .53 and .66 for assumed passage rates of .02 and .06 h(-1), respectively. For the forages evaluated in this study, these results indicate that neutral detergent soluble N may make important contributions to the pool of N escaping ruminal degradation.     

纤维素酶对粗饲料人工瘤胃pH、氨态氮及产气量的影响

本试验分别以棉籽壳、苜蓿、小麦秸秆、玉米青贮、玉米秸秆为底物,采用人工瘤胃技术,研究不同水平纤维素酶对人工瘤胃pH、氨态氮浓度及产气量的影响。对照组未添加纤维素酶,试验1、2和3组分别添加纤维素酶140、280、420IU/mL。结果表明,不同水平纤维素酶的人工瘤胃pH无显著变化(P>0.05),氨态氮浓度变化不显著(P>0.05),但人工瘤胃最大产气量显著提高(P<0.05)。     

Amino acid profiles of rumen undegradable protein: a comparison between forages including cereal straws and alfalfa and their respective total mixed rations

Optimizing the amino acid (AA) profile of rumen undegradable protein (RUP) can positively affect the amount of milk protein. This study was conducted to improve knowledge regarding the AA profile of rumen undegradable protein from corn stover, rice straw and alfalfa hay as well as the total mixed ratio diets (TMR) based on one of them as forage source [forage‐to‐concentrate ratio of 45:55 (30% of corn stover (CS), 30% of rice straw (RS), 23% of alfalfa hay (AH) and dry matter basis)]. The other ingredients in the three TMR diets were similar. The RUP of all the forages and diets was estimated by incubation for 16 hr in the rumen of three ruminally cannulated lactating cows. All residues were corrected for microbial colonization, which was necessary in determining the AA composition of RUP from feed samples using in situ method. Compared with their original AA composition, the AA pattern of forages and forage‐based diets changed drastically after rumen exposure. In addition, the extent of ruminal degradation of analysed AA was not constant among the forages. The greatest individual AA degradability of alfalfa hay and corn stover was Pro, but was His of rice straw. A remarkable difference was observed between microbial attachment corrected and uncorrected AA profiles of RUP, except for alfalfa hay and His in the three forages and TMR diets. The ruminal AA degradability of cereal straws was altered compared with alfalfa hay but not for the TMR diets. In summary, the AA composition of forages and TMR‐based diets changed significantly after ruminal exposure, indicating that the original AA profiles of the feed cannot represent its AA composition of RUP. The AA profile of RUP and ruminal AA degradability for corn stover and rice straw contributed to missing information in the field.     

Effects of feed intake on in situ rumen microbial contamination and degradation of feeds

An in situ study was conducted using four rumen cannulated wethers and five feeds (corn grain (CG), soybean meal (SBM), sunflower meal (SFM), vetch–oat hay (VH), and lentil straw (LS)) to determine (using ¹⁵N infusion techniques) the effects of two intake levels (40 and 80 g DM/kg W^0.75) on the microbial contamination and rumen degradation of DM or CP. Degradation studies were also performed for neutral and acid detergent fibres (NDF and ADF, respectively) of VH. In most cases, the evolution with time of the microbial DM adhered to particles fitted well to exponential curves, which diverged between both levels of intake due to the lower values attained at high intake. However, as a consequence of the large and progressive increase of the variability of microbial contamination, statistical evidence is only partial. This behaviour was less evident for CP contamination, especially in forages. The lack of these corrections underestimated (P < 0.001) the effective degradability (ED) of all tested fractions, with important differences between feeds. The intake level had not relevant effects on the distribution of soluble, insoluble available and unavailable fractions of DM or CP (or fibres in VH), but determined some changes in their degradation rates (k_d). Direct relations between these last values and rumen outflow rates (k_p) were shown in some feeds for the degradation of CP and also of DM in concentrates, whereas negative relations were shown for the degradation rates of DM in forages (or NDF and ADF of VH). All ED estimates decreased with the intake rise, but for CP this effect (P < 0.05) was only detected in SBM and VH. These decreases represent 40.8 (CG), 80.8 (SBM), 62.1 (SFM), 66.8 (VH), and 19.5% (LS) than those estimated considering only k_p changes, which shows the interest to consider conjointly the variations of both rates to study the effect of diet changes on ED.     

Correcting the calculation of extent of degradation to account for particulate matter loss at zero time when applying the polyester bag method

The established calculation of ruminal extent of degradation using the polyester bag method overestimates extent. The wash fraction, at least in part, is subject to losses from the rumen due to passage. Four formulae are proposed to minimize this risk of overestimation. Four options are considered: 1) passage losses for particulate matter escaping from the bag at zero time are according to the particulate fractional passage rate, 2) the liquid rate, and 3) the average of the two, and additionally 4) there is no instantly degradable fraction. The established and proposed formulae were examined using polyester bag data for six forages: grass silage, fresh ryegrass, fresh white clover, alfalfa hay, mixed grasses hay, and hay from a permanent mountain meadow. The established formula gave appreciably higher estimates of extent of degradation in all cases. Overestimation was at least 6.9, 4.9, 2.9, 2.1, 2.4, and 4.5%, respectively, for the six forages.     

Extent and site of mineral release from six forage species incubated in mobile dacron bags

A study was conducted to measure the extent of DM disappearance and mineral release from six forage species within the rumen, abomasum and intestines of the adult bovine using the mobile bag technique. Three nonlactating Holstein cows, fitted with ruminal and duodenal cannulas, were given ad libitum access to alfalfa hay. One gram (DM) of alfalfa, rhizoma peanut, dwarf elephantgrass, bahiagrass, bermudagrass, and limpograss was individually weighed into 8-cm x 3-cm dacron bags. After ruminal incubation for 24 h, bags were incubated in an acid-pepsin solution (a simulated abomasal environment) for 1 h, inserted into the duodenum via cannula, and collected in the feces upon excretion. Ruminal incubation accounted for 86% to 100% of total DM disappearance. Release of Ca from all forages was at least 65%, with the majority having extents of release of over 70%. Most Ca was released in the rumen, but acid-pepsin incubation and washing increased Ca release an additional 17 to 272%. Forages with the highest NDF concentration (bermuda, bahia, and limpograss) sequestered Ca in the intestines. Total tract P release ranged from 84 to 98%, with an average of 7.5 percentage units occurring postabomasally. Grasses released more P in the intestines than legumes. Eighty-eight to 98% of total Mg was released in the rumen. Acid-pepsin incubation increased Mg release only slightly, with some Mg being sequestered in the intestines. Potassium release was complete in the rumen. Ranking of minerals based on maximal extent of release was K greater than Mg greater than P greater than Ca. With the exception of K, legumes released more of their minerals than grasses.     

不同牧草在肉羊瘤胃中的降解特性研究

为研究不同牧草干物质(DM)及蛋白质(CP)在肉羊瘤胃中的降解规律,以3头安装有永久性瘤胃瘘管的杜×寒肉用绵公羊为试验动物,采用半体内法对13种牧草的DM和CP的降解率和降解参数进行测定。结果表明:苜蓿DM和CP在瘤胃内各个时间点的降解率最高(P<0.05);沙打旺、狗尾草、燕麦草、草地早熟禾72 h降解率显著高于其他牧草(P<0.05)。13种牧草DM的可降解部分和有效降解率的高低顺序与DM在不同时间点的降解高低顺序类似。豆科苜蓿和沙打旺CP的有效降解率最高(P<0.05);禾本科燕麦草、象草、草地早熟禾和狗尾草CP的有效降解率显著高于其他禾本科牧草(P<0.05)。苜蓿慢速降解部分的降解速率显著高于其他牧草(P<0.05)。由此得出,豆科牧草苜蓿、沙打旺DM和CP的降解率高于禾本科牧草。燕麦草、草地早熟禾、象草、狗尾草的降解率较高;冷地早熟禾、多叶老芒麦、羊草、披碱草的降解率居中;芨芨草、中华羊茅和芦苇的降解率偏低。     

Ruminal protein degradation and protein value of feeds

The relationship between dry matter (DM) degradation and crude protein (CP) degradation in the dairy cow's rumen was determined with a view to defining the protein value of feeds for ruminants. The nylon bag technique was applied for these studies. For all the feeds investigate (green fodder and preserves from cocks-foot, ryegrass, alfalfa/grass and meadow grass, as well as alfalfa, extracted soybean meal) a significantly positive relationship was found to exist between the levels of DM and CP degradation (r = 0.73 to 1.0). The regression coefficient b1 (CP degradation as regressor) was found to average 0.87. The positive relationship between DM degradation and CP degradation implies that microbial protein amount and unfermented feed protein at the duodenum are negatively correlated. Model calculations show that, on account of the compensation between microbial protein and feed protein at the duodenum, in feeds with a CP concentration below 200 g/kg DM, the extent of ruminal protein degradation does not exert a marked influence on duodenal protein passage. The partial calculation of the duodenal protein supply on the basis of undegraded feed protein and microbial protein, as practiced in the new models of protein evaluation, leads to systematic errors unless the relationship between DM degradation and CP degradation is considered.     

Ruminal solubility of nitrogen and minerals from fescue and fescue-red clover herbage

Ruminal solubility of N, K, P, Ca, Mg and S were measured for three forages at six growth stages. The three forages were Kentucky 31 tall fescue (TF), Kenhy fescue (KN) and a red clover-tall fescue mixture (RC). Disappearance parameters were measured by means of the dacron bag technique using cannulated steers. Exposures were for 48 h; maximum extent of disappearance for all elements occurred before this time. High proportions (greater than 60%) of P, K and Mg were released from all three forages during the first 3 h of incubation, with small losses thereafter. Amounts of N and S released during the first 3 h ranged between 40 to 75%. Ca had the lowest initial disappearance. Forages differed (P less than .05) in extent of mineral disappearance after 3- and 48-h incubations and in rate of disappearance (Kd) of the potentially available, slowly solubilizing, fraction of N, Ca and S. Across growth stages, TF had generally the lowest extent and rate of disappearance. With increasing maturity, Kd for Mg, Ca and S decreased (P less than .05). For each element, Kd was not correlated with herbage concentration or initial (3 h) disappearance. Partial correlations between disappearance of N, K, Ca, Mg and S after the 48-h incubation and herbage concentration were significant. Solubilization values corrected for rate of passage (ERS) showed significant differences among forages for K, Ca and S. Average ERS values for S and K were highest for KN; RC herbage had higher ERS values for Ca. Increases in forage maturity lowered (P less than .001) ERS for all elements. The results indicate that for all growth stages, ruminal solubility and potential availability of N and minerals from the three forages was high. The rate of release differed among elements and may have affected efficiency of microbial fermentation. Although ruminal solubility of minerals from TF was generally lower than from the other two forages, the difference was not sufficient to explain fully the lower apparent availability observed in previous studies.     

Combinations of high-moisture harvested sorghum grain and dry-rolled corn: effects on site and extent of digestion in beef heifers

To determine the effects of blends of high-moisture harvested sorghum grain (HMS) and dry-rolled corn (DRC) on site and extent of digestion, high-grain diets were fed to Angus-Hereford heifers (315 kg) in a 5 x 5 latin square. The grain portion consisted of ratios (HMS:DRC) of 0:100, 25:75, 50:50, 75:25 and 100:0. Heifers were equipped with ruminal, duodenal and ileal T-type cannulas. Digestibilities of OM (P less than .05) and non-ammonia nitrogen (NAN; P less than .01) in the total tract declined linearly as HMS replaced DRC. Chyme flow (liters/d) through the duodenum increased linearly (P less than .01), and true ruminal OM disappearance tended to decline linearly (P less than .10) as HMS replaced DRC. A quadratic response (P less than .05) in extent of starch disappearance (g/d) in the rumen was noted; blends were lower than either individual grain. Ruminal escape of feed N tended to be quadratic (P less than .10); values for individual grain types were greater than blends. Microbial efficiency increased linearly (P less than .05) as HMS replaced DRC. Extent of starch digestion in the rumen averaged 82.7% compared to only 2.9% in the small intestine and 5.7% in the large intestine. Altering the ratio of HMS to DRC appeared to have more effect on ruminal fermentation than on digestion in the small intestine; most starch and nitrogen responses were quadratic. Increases in ruminal pH and chyme flow, potentially caused by increased salivary flow, may cause non-linear changes in the solubility of proteins in HMS and DRC, when fed as blends, altering the digestibility of protein and starch from values predicted from the individual grains.     

ORIGINAL ARTICLE: Ruminal and total tract phosphorus release from feedstuffs in cattle measured using the mobile nylon bag technique

Phosphorus (P) excretion in manure is a concern for dairy and beef producers. Excess P released into surface water runoff can lead to eutrophication and algal blooms in streams and lakes. One approach to reducing P excretion is to reduce dietary P. Data regarding P release from feedstuffs is limited and more precise formulations based on specific feed P release in the digestive tract may be one way to lower excreted P. In this experiment, the mobile nylon bag technique was used to determine the disappearance of P in corn silage, alfalfa hay, Coastal bermudagrass hay, and Tifton‐85 bermudagrass hay in steers after ruminal (24 h), ruminal + pepsin/HCl (rumen + PHCl), and ruminal + pepsin/HCl + intestinal (rumen + PHCl + I) incubation. Ruminal disappearance of P differed (p < 0.05) between feedstuffs and by site of incubation. Total tract (rumen + PHCl + I) P disappearance for corn silage, alfalfa hay, Coastal bermudagrass hay, and Tifton‐85 bermudagrass hay were 90.6%, 93.7%, 83.8% and 84.0% respectively. The range in P release (approximately 7%) indicates that considering P availability when balancing rations could have a measurable impact on subsequent P excretion from ruminants. More data concerning P availability as affected by other feed ingredients or plant species, maturity, and/or quality are needed to more accurately define P release from ruminant feeds.     

Propionic acid disappearance from the foregut and small intestine of the beef steer

Studies were conducted to determine the disappearance of propionic acid from the rumen and across the small intestine. Four crossbred beef steers, fitted with ruminal, duodenal and ileal cannulas, were given pulsed-continuous infusions of a nonabsorbable liquid phase marker (CrEDTA) and buffered propionic acid to achieve ruminal propionate productions (RPP) of 142 (basal), 567 and 997 mmol/h. Liquid flows from the rumen, and at the duodenum and ileum (2.75, 3.57 and .92 liters/h, respectively) were not affected by RPP (P greater than .23), although significant differences existed between sites (P = .001), reflecting a net addition of liquid between the rumen and duodenum and a net removal of liquid within the small intestine. Propionate disappearance from the rumen was 40 to 57% irrespective of RPP, with the complement passing from the rumen. Of the propionate that exited the rumen, 93 to 97% disappeared prior to entering the duodenum. Overall removal of RPP prior to the duodenum was 97 to 99% irrespective of RPP. Passage of propionic acid at the duodenum and at the ileum did not differ (P greater than .76) across all RPP, and the overall mean passages did not differ from zero (P greater than .34); similar results were observed for other VFA. These observations indicate that essentially all RPP is removed prior to entering the small intestine. Additionally, net propionate disappearance across the small intestine was undetectable and likely biologically irrelevant. Therefore, VFA absorption does not appear to be a limiting biological process in the beef steer.     

不同发酵时间对全混合日粮的瘤胃降解特性以及小肠消化率的影响

试验旨在研究发酵0、3、7、15、30 d的全混合日粮(TMR)对瘤胃降解特性以及小肠消化率的影响。选用3头体重为550 kg左右、安装有永久性瘤胃瘘管的荷斯坦奶牛,采用尼龙袋法和三步体外法测定发酵全混合日粮(FTMR)的干物质(DM)、粗蛋白质(CP)、中性洗涤纤维(NDF)的瘤胃降解率以及瘤胃未降解蛋白(RUP)的小肠消化率。结果表明:随着发酵时间的延长,FTMR饲料的DM含量显著降低(P<0.05);随着发酵时间的延长,显著提高FTMR的DM、CP、NDF的瘤胃降解率(P<0.05)和CP、NDF的快速降解部分(P <0.05);同时发酵显著降低RUP的小肠消化率(P <0.05)。综上可知,全混合日粮提高了DM、CP和NDF在瘤胃中的瘤胃降解率,15、30 d的FTMR各营养成分的瘤胃降解性较好;RUP的小肠消化率随发酵时间的延长开始逐渐降低,7d之后降低最为明显。因此,应控制好TMR的发酵时间,以便更有效地利用饲料资源。     

Ruminal fermentation pattern, bacterial population and ruminal degradation of feed ingredients as influenced by ruminal ammonia concentration

The effects of ruminal ammonia concentration on bacterial numbers, fermentation pattern and degradation of feed ingredients in the rumen were examined with three nonlactating Holstein cows fitted with ruminal cannulas. Cows were fed twice daily a complete mixed diet (90% whole plant oat silage and 10% concentrate mixture) containing 11.1% CP on a DM basis. Ammonium bicarbonate (NH4HCO3) was infused continuously into the rumen at levels of 0, 95, 190 or 280 g/d. Infusion of NH4HCO3 linearly increased (P less than .05) the concentrations of ruminal ammonia and blood urea N. Total VFA concentrations and mixed bacterial numbers also were increased (P less than .05) by NH4HCO3 infusion. Infusions of NH4HCO3 increased (P less than .05) butyrate and decreased (P less than .05) isobutyrate and isovalerate proportions. Infusion of NH4HCO3 increased (P less than .05) rate of degradation of soybean meal DM but did not (P greater than .05) influence degradation characteristics of fish meal and barley grain. In conclusion, supplementation of N by continuous infusion of NH4HCO3 appeared to stimulate bacterial growth and fermentation but it did not influence extent of ruminal degradation of selected feed ingredients.     

尼龙袋法评价香蕉叶单宁对瘤胃降解特性的影响

旨在探究香蕉叶单宁对奶牛瘤胃降解特性的影响和评价香蕉叶的饲喂价值。样品分别为苜蓿干草组(100%的苜蓿干草)、苜蓿干草和香蕉叶混合组(50%苜蓿干草+50%香蕉叶)、香蕉叶组(100%香蕉叶)、苜蓿干草组(100%的苜蓿干草)+6%聚乙二醇(6% PEG)、苜蓿干草和香蕉叶混合组(50%苜蓿干草+50%香蕉叶)+6%聚乙二醇(6% PEG)、香蕉叶组(100%香蕉叶)+6%聚乙二醇(6% PEG)。测定样品中的营养成分含量,使用3头安装了瘤胃瘘管的荷斯坦奶牛进行半体内试验,用尼龙袋法测定上述样品在瘤胃内0、2、4、8、12、24、48、72 h的干物质(DM)、粗蛋白质(CP)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)的降解率,得到各营养物质的动态降解参数。结果表明,相较于苜蓿干草,香蕉叶干物质和粗蛋白的快速降解部分、慢速降解部分、慢速降解部分的降解速率、有效降解率是显著低于苜蓿干草的(P<0.001),香蕉叶和苜蓿的NDF的有效降解率没有显著差异。添加了PEG后,香蕉叶和香蕉叶苜蓿混合组的快速降解部分和有效降解率显著高于未添加PEG的两组(P<0.001)。结果表明香蕉叶中的单宁会抑制香蕉叶的瘤胃降解率,因此在使用香蕉叶调制反刍动物的饲料时需要控制单宁的含量。     

Apparent ruminal degradation and rumen escape of soluble nitrogen fractions in grass and grass silage administered intraruminally to lactating dairy cows

The main objective of this study was to investigate in vivo ruminal degradation and rumen escape of soluble N fractions in grass and grass silage. Soluble protein and long-chain peptides (PLP), small peptides (SP) and free AA (FAA) were obtained from fresh grass and grass silages fertilized with different levels of N. Soluble extracts from the forages were pulse dosed into the rumen of three cannulated lactating dairy cows, and a simple or complex model was used to examine the kinetics of the soluble N fractions in the rumen. When soluble extracts from silage were investigated, pulse dosages of total nonammonia N (NAN) were 21, 27, and 32 g, while for fresh grass only dosages of 20 g were ruminally administered. In the silage extracts, mean proportions of PLP-N, SP-N, and FAA-N in the NAN were 30, 52, and 18%, respectively, whereas in the fresh grass the corresponding values were 67, 20, and 13%. From silage extracts, all three soluble N fractions showed a linear decrease (P < 0.05) in degradation rate and an increase (P < 0.05) in ruminal escape with increasing dosage. In silage, mean degradation rates, parameterized from the complex model, were 230, 214, and 334%/h for PLP-N, SP-N, and FAA-N, respectively, and the ruminal escape was highest (P < 0.05) for SP-N (11.2% of dose) and lowest (P < 0.05) for FAA-N (5.0% of dose). No differences in degradation rate and ruminal escape between fresh grass and silage were observed. However, the proportion of N dose converted to ammonia was only 24% in the fresh grass, whereas for the silages a mean value of 76% was found. From this study, it is concluded that a significant amount of dietary soluble N escapes ruminal degradation, and thus contributes to the intestinal AA supply. Moreover, if the main aim is to study degradation kinetics of individual N fractions, a complex model should be used in the evaluation. This model can also be used to study ruminal synchronization of N and energy for microbial growth.     

我国北方地区奶牛常用饲料蛋白质组分及其降解规律的研究

本试验研究以NRC(2001)奶牛营养需要(第7版)采用的对粗蛋白质组分的分析方法为基础,对奶牛养殖中常用的部分饲料原料进行取样分析,利用尼龙袋法测定出这些常用饲料原料的各种蛋白质组分(A、B、C)和B组分的降解速率。结果表明,粗饲料的粗蛋白质中A组分和C组分的比例较高,A组分变异较大;B组分的比例相对较小,在瘤胃中的降解速率较低。精料的粗蛋白质中B组分的含量较高,而C组分的含量较低。因而,精料是反刍动物瘤胃降解蛋白质(RDP)和瘤胃非降解蛋白质(RUP)的主要来源。     

Ruminal in situ disappearance kinetics of nitrogen and neutral detergent insoluble nitrogen from common crabgrass forages sampled on seven dates in northern Arkansas

Southern crabgrass (Digitaria ciliaris [Retz.] Koel.) is often an undesirable species in field and forage crops, but visual observations suggest that livestock prefer it to many other summer forages. The objectives of this study were to assess the nutritive value of crabgrass sampled weekly between July 11 and August 22, 2001 and then to determine ruminal in situ disappearance kinetics of N and neutral detergent insoluble N (NDIN) for these forages. A secondary objective was to compare these kinetic estimates for crabgrass with those of alfalfa (Medicago sativa L.), bermudagrass (Cynodon dactylon [L.] Pers.), and or-chardgrass (Dactylis glomerata L.) as control hays. All kinetic evaluations were conducted with 5 ruminally cannulated Gelbvieh x Angus x Brangus steers (383 +/- 22.7 kg). Concentrations of N for crabgrass decreased linearly (P < or = 0.002) across sampling dates for leaf, stem, and whole-plant tissues. Conversely, percentages of the total N pool within NDIN and ADIN fractions generally increased over sampling dates in mostly linear patterns. For crabgrass, the immediately soluble portion of the total N pool (fraction A; overall mean = 54.6% of N) was greater (P < 0.001) than for all control hays. Crabgrass exhibited a more rapid N disappearance rate (overall mean = 0.093/h; expressed as a proportion disappearing/h) than that of bermudagrass (0.046/h; P < 0.001), but the disappearance rate for alfalfa N (0.223/h) was considerably faster (P < 0.001) than for crabgrass. The effective ruminal disappearance of N was greater (P < 0.001) for crabgrass (overall mean = 85.4%) than for the alfalfa (83.3%), bermudagrass (72.3%), or orchardgrass (76.0%) control hays. For alfalfa, the ruminal disappearance rate of NDIN (0.150/h) was more rapid (P < 0.001) than for crabgrass (overall mean = 0.110/h); however, the disappearance rate for crabgrass was faster than that for bermudagrass (0.072/h; P < 0.001) or for orchardgrass (0.098/h; P = 0.010). Effective ruminal disappearance of NDIN was greater (P < 0.001) for crabgrass (overall mean = 72.0%) than for the bermudagrass (69.0%) or alfalfa hays (50.5%), but there was no difference (P = 0.865) between crabgrass and orchardgrass (72.1%). Although crabgrass forages exhibited concentrations of total N that were comparable with those of alfalfa and rates of ruminal N disappearance that were < 50% of those for the alfalfa hay control, improvements in N use efficiency relative to alfalfa are questionable because of the excessively large Fraction A for crabgrass.