Predicting forage indigestible NDF from lignin concentration

Evaluation of different mathematical models on fitting the in vitro gas production parameters in beef cattle

In vitro rumen gas production experiment was conducted with 57 kinds of feedstuff, which were categorized into energy feed, protein feed, and roughage, collected within China. Eight mathematical models were employed to describe the kinetics of in vitro rumen gas production. The results found that for energy feeds, protein feeds, and roughages, respectively, Michaelis-Menten (MM) or Logistic-Exponential with lag (LEL), MM, and Mitscherlich (MIT) exhibited the highest or shown no significant difference compared to the highest coefficient of determination (R2) (P < 0.05) for all categories of feed. Furthermore, regression estimation of intercept and slope for regression estimates of intercept and slope for Observed versus Predicted of aforementioned models shown no significant difference from 0 and 1, respectively (P < 0.05), except LEL for energy feed. Mean absolute error (MAE), root mean squared error of prediction (RMSEP), mean squared error of prediction (MSEP) of those models were relatively lower, with minimal systematic bias and regression bias. Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) rankings were higher compared with other models. Given these results, in studies where feedstuff categories are not distinguished or multiple feedstuffs categories are included, the MM model proves to be a good choice. MM or LEL was considered to better fit energy feedstuffs. The MM model was the optimal choice for fitting protein feedstuffs. MIT provided the best accuracy and moderate precision when fitting roughages.

Effects of ensiling time on corn silage neutral detergent fiber degradability and relationship between laboratory fiber analyses and in vivo digestibility

Accurate analysis of degradability of silage neutral detergent fiber (NDF) is important for diet formulation and to predict lactational performance of dairy cows. In this study, 5 corn silage hybrids ensiled for 0 (unfermented), 30, 60, 120, and 150 d were used to determine the effects of ensiling time on silage neutral detergent fiber degradability (NDFD) and to assess the relationships between near-infrared reflectance spectroscopy (NIR) NDF-related analyses and in situ NDFD variables. In addition, the relationships between dietary concentration of indigestible NDF, 288-h incubation (iNDF288), or undegraded NDF, 240-h incubation (uNDF240), and in vivo total-tract apparent organic matter and NDF digestibility were studied in total mixed ration samples from 16 experiments with lactating dairy cows. Ensiling time had no effect on silage NDF concentration; however, the ratio of acid detergent fiber ÷ NDF increased, and estimated hemicellulose concentration decreased quadratically with ensiling time. Also, concentration of NDF-bound protein decreased, and that of lignin increased linearly with ensiling time. These changes in silage fiber composition resulted in a linear decrease in in situ effective degradability of silage NDF with increasing ensiling time. The indigestible fraction of NDF and concentration of structural carbohydrates were not affected by ensiling time. Correlations of in situ NDFD variables with laboratory NIR NDFD analyses were weak to moderate. The relationship of corn silage uNDF240 with lignin concentration or 30-h NDFD (all NIR analyses) was remarkably good (R² = 0.73 and 0.88, respectively). The relationship between in situ iNDF288 concentration (but not uNDF240) and in vivo total-tract apparent digestibility of dietary organic matter and NDF was good (R² = 0.72 and 0.80, respectively). In conclusion, in situ degradability of silage NDF linearly decreased from 0 to 150 d ensiling time, primarily caused by a decrease in concentrations of hemicellulose and NDF-bound protein. In situ NDF degradability measurements and common laboratory NIR NDF-related analyses were generally poorly correlated. We found a good relationship between in vivo NDF digestibility and dietary concentration of iNDF288 determined in situ, but the relationship with uNDF240 was poor.

Produção e composição do leite em função da alimentação de vacas mestiças Holandês x Zebu confinadas em condições experimentais no Brasil - Metanálise

RESUMO Objetivou-se avaliar os fatores da composição da dieta que podem interferir no consumo, na digestibilidade, na produção e na composição do leite de vacas mestiças Holandês x Zebu confinadas em condições experimentais no Brasil. A metanálise foi utilizada para o levantamento de trabalhos científicos de domínio público, compreendendo o período de janeiro de 2000 a dezembro de 2015. A base de dados foi constituída por 40 experimentos com 159 tratamentos, envolvendo 735 vacas em lactação. O consumo de nutrientes digestíveis totais (NDT) é comprometido pelo teor de fibra em detergente ácido (FDA) da dieta, relacionando-se com a digestibilidade da matéria seca (MS) e da fibra em detergente neutro (FDN), o que repercute na eficiência alimentar (EA). Observa-se a relação do teor de carboidratos não fibrosos (CNF) da dieta com o teor de lactose e o efeito do teor de MS da dieta e o elevado teor de FDN no consumo em função das características específicas dos tipos de volumosos utilizados. O consumo de NDT da dieta é prejudicado pela digestibilidade da MS e, principalmente, da FDN em função da proporção e das características dos volumosos utilizados na dieta, e esses fatores repercutem na EA, bem como na produção e na composição do leite.

Estimating digestible energy values of feeds and diets and integrating those values into net energy systems

The California Net Energy System (CNES) used a combination of measured and tabular metabolizable energy (ME) values and changes in body composition gain to determine net energy requirements for maintenance and gain and their corresponding dietary concentrations. The accuracy of the CNES depends on the accuracy of the feed ME values. Feed or diet ME values can be measured directly but are expensive and require specialized facilities; therefore, most ME values are estimated from digestible energy (DE) values, which are often estimated from the concentration of total digestible nutrients (TDN). Both DE and TDN values are often from tables and not based on actual nutrient analysis. The use of tabular values eliminates important within-feed variation in composition and digestibility. Furthermore, the use of TDN to estimate DE does not account for important variation in the gross energy value of feeds. A better approach would be to estimate DE concentration directly from nutrient composition or in vitro (or in situ) digestibility measurements. This approach incorporates within-feed variation into the energy system and eliminates the issues of using TDN. A widely used summative equation based on the commonly measured feed fractions (ash, crude protein, neutral detergent fiber, and fat) has been shown to accurately estimate DE concentrations of many diets for cattle; however, deficiencies in that equation have been identified and include an overestimation of DE provided by fat and an exaggerated negative effect of intake on digestibility. Replacing the nonfiber carbohydrate term (which included everything that was not measured) in the equation with measured starch concentration and residual organic matter (i.e., nonfiber carbohydrate minus starch) should improve accuracy by accounting for more variation in starch digestibility. More accurate estimates of DE will improve the accuracy of ME values, which will ultimately lead to more accurate NE values.

Effect of variety and stage of maturity at harvest on nutrient and neutral detergent fiber digestibility of forage barley grown in western Canada

This study evaluated the effect of variety (V; CDC Cowboy, CDC Copeland, and Xena) and stage of harvest maturity (M; milk, early-, mid-, and hard-dough) on nutrient and neutral detergent fiber digestibility (NDFD) characteristics of barley forage using a randomized complete block design with 3 × 4 factorial treatment arrangement. Barley varieties had similar crude protein, but CDC Cowboy had greater (P < 0.01) acid detergent fiber (ADF), neutral detergent fiber (NDF), and lignin, and lower (P < 0.01) total digestible nutrient (TDN) content relative to Xena. Starch content of CDC Cowboy was lower (P < 0.01) than Xena at all stages of maturity with CDC Copeland intermediate at early- and mid-dough stages. Crude protein, ADF, NDF, and lignin content decreased (P < 0.01) while starch and TDN content increased (P < 0.01) with advancing maturity. Xena had greater (P < 0.01) NDFD, as determined by 6 h in vitro incubation using DaisyII system (NDFD6h), at milk, mid- and hard-dough stages of maturity than CDC Cowboy with CDC Copeland intermediate at mid-dough. However, CDC Cowboy had greater (P < 0.01) NDFD, as determined by 30 h in vitro incubation using DaisyII system (NDFD30h), at early-dough stage than Xena and greater NDFD30h at hard-dough stage than CDC Copeland. Xena had the lowest (P < 0.01) indigestible NDF based on 288 h ruminal in situ incubation (INDF288h), relative to CDC Copeland. These results indicate that to optimize NDFD30h, variety should be considered when deciding the timing of harvest.

Comparative study of some analytical methods to quantify lignin concentration in tropical grasses

Objective

Lignin plays a relevant role in the inhibition of cell wall (CW) structural carbohydrate degradation. Thus, obtaining accurate estimates of the lignin content in tropical plants is important in order to properly characterize the mechanism of lignin action on CW degradation. Comparing conflicting results between the different methods available for commercial use will bring insight on the subject. This way, providing data to better understand the relationship between lignin concentration and implications with tropical forage degradation.

Methods

Five grass species, Brachiaria brizantha cv Marandú, Brachiaria brizantha cv Xaraés (MG-5), Panicum maximum cv Mombaça, Pennisetum purpureum cv Cameroon, and Pennisetum purpureum cv Napier, were harvested at five maturity stages. Acid detergent lignin (ADL), Klason lignin (KL), acetyl bromide lignin (ABL), and permanganate lignin (PerL) were measured on all species. Lignin concentration was correlated with in vitro degradability.

Results

Highly significant effects for maturity, lignin method and their interaction on lignin content were observed. The ADL, KL and ABL methods had similar negative correlations with degradability. The PerL method failed to reliably estimate the degradability of tropical grasses, possibly due to interference of other substances potentially soluble in the KMnO₄ solution.

Conclusion

ADL and KL methods use strong acid (H₂SO₄) and require determination of ash and N content in the lignin residues, therefore, increasing time and cost of analysis. The ABL method has no need for such corrections and is a fast and a convenient method for determination of total lignin content in plants, thus, it may be a good option for routine laboratory analysis.

A nutritional evaluation of common barley varieties grown for silage by beef and dairy producers in western Canada

This study evaluated the nutritional and neutral detergent fiber digestibility (NDFD) characteristics of seven barley varieties (‘Conlon’, ‘CDC Copeland’, ‘CDC Cowboy’, ‘Falcon’, ‘Legacy’, ‘AC Metcalfe’, and ‘Xena’) grown for silage. Commercial samples (n = 80) harvested at the mid-dough stage were collected over 2 years (2012 and 2013). Average pH and dry matter (DM) content were 4.05% ± 0.17% and 36.8% ± 4.1%, respectively. ‘Falcon’ and ‘AC Metcalfe’ had higher (P < 0.05) CP relative to ‘CDC Copeland’ and ‘Xena’, with intermediate values for the other varieties. Acid (ADF) and neutral (NDF) detergent fiber contents were higher (P < 0.05) for ‘CDC Cowboy’ relative to ‘Conlon’. Starch was higher (P < 0.05) for ‘Legacy’ and ‘Conlon’ than ‘CDC Cowboy’, with intermediate values for other varieties. Legacy had a greater (P < 0.05) 6-h NDFD while ‘CDC Cowboy’ had a greater (P < 0.05) 30-h NDFD. Indigestible NDF (INDF; % NDF) was greater (P < 0.05) for ‘AC Metcalfe’ relative to ‘CDC Cowboy’ and ‘Falcon’. These results indicate that barley varieties vary with respect to chemical composition and NDFD and INDF contents. Selection for higher 30-h NDFD could result in improvements in DM and DE intake and performance of growing beef cattle.

Estimation of the indigestible fiber in different forage types

The role of indigestible NDF is essential in relation to OM digestibility prediction, total tract digestibility, rumen fill, passage rate, and digestion kinetics. Moreover, the truly indigestible NDF (iNDF) represents a core point in dynamic models used for diet formulations. However, despite its wide possible applications, few trials have been conducted to quantify iNDF and even fewer to investigate whether or not it is consistent among different forage sources. The objective of this study was to predict the iNDF by measuring the residual NDF after 240-h in vitro fermentation to determine the unavailable NDF (uNDF) within and among various forage types. Finally, a mathematical approach was investigated for the estimation of the uNDF fraction. In all, 688 forages were analyzed in this study. This pool included 122 alfalfa hays, 282 corn silages, and 284 grass hays. Values of uNDF varied among different forages and within the same type (22.7% ± 4.48%, 20.1% ± 4.23%, and 11.8% ± 3.5% DM for grass hay, alfalfa hay, and corn silages, respectively). The relationship among uNDF and ADL was not constant and, for grass hay and corn silage, was different ( 0.05) from the 2.4 × lignin value applied by the traditional Chandler equation. The observed uNDF:ADL ratio was 3.22 for grass hay and 3.11 for corn silage. Relationships among chemical and biological parameters and uNDF were investigated via simple and multiple regression equations. The greatest correlation with a single variable was obtained by ADL and ADF when applied to the whole data set ( = 0.63). Greater coefficients of determination resulted from a multiple regression equation for the whole data set ( = 0.80) and within each forage type ( = 0.65, 0.77, and 0.54 for grass hay, alfalfa hay, and corn silage, respectively). In conclusion, a regression approach requires specific equations and different regression coefficients for each forage type. The direct measurement of uNDF represented the best approach to obtain an accurate prediction of the iNDF and to optimize its specific purpose in dynamic nutrition models.

Influence of maturity on alfalfa hay nutritional fractions and indigestible fiber content

This study focused on changes in fibrous and protein fractions, changes in fiber digestibility and amount of indigestible neutral detergent fiber (NDF) as a consequence of increased maturity in alfalfa. A total area of 720 m(2) was divided in 18 blocks randomly assigned to 3 treatments, differing in cutting intervals. Treatment 1 was harvested with a 21-d cutting schedule, at a prebloom stage; treatment 2 with a 28-d schedule, at about first-bloom stage; whereas a full bloom was observed in treatment 3, harvested with a 35-d cutting schedule. Treatments were replicated 4 times through the spring-summer period for 2 subsequent years, 2011 and 2012. Statistical differences were observed for crude protein [treatment 1: 20.8%, treatment 2: 17.3%, and treatment 3: 17.0%; standard error of the mean (SEM)=0.83], soluble protein, and nonprotein nitrogen among treatments on a dry matter basis. Similar results were observed for acid detergent lignin (6.3, 6.9, and 7.3%, respectively; SEM=0.39), lower in treatment 1 compared with others, and in vitro NDF digestibility at 24 or 240 h. Indigestible NDF at 240 h resulted in lower values for treatment 1 compared with treatments 2 and 3 (15.5, 17.2, and 18.3%, respectively; SEM=1.54). Moreover, the indigestible NDF:acid detergent lignin ratio varied numerically but not statistically among treatments, being as much as 9% greater than the 2.4 fixed value applied for rate of digestion calculation and Cornell Net Carbohydrate Protein System (Cornell University, Ithaca, NY)-based model equations. Assuming the diet composition remained unchanged, treatment 3 (35-d cutting interval) would be expected to yield 1.4 kg less milk per day based on energy supply, and 2.8 kg less milk daily based on protein supply than treatment 1.

Invited Review: Ethanol co-products for dairy cows: there goes our starch … now what?

Paz, H. A., Castillo-Lopez, E., Ramirez-Ramirez, H. A., Christensen, D. A., Klopfenstein, T. J. and Kononoff, P. J. 2013. Invited Review: Ethanol co-products for dairy cows: there goes our starch … now what? Can. J. Anim. Sci. 93: 407–425. The rise of the grain-ethanol industry has resulted in a dramatic increase in the availability of feed co-products namely, distillers’ grains with solubles (DG). The cost of feeds that have traditionally been used for energy continues to increase and there is a need to understand the potential impact of replacing these feeds with DG on milk yield and composition. Using the Dairy National Research Council (2001) model and data from a total of 25 published studies (81 observations), we used a meta-analytical procedure to evaluate the impact of feeding corn milling co-products on lactating dairy cows. Based on our model, the inclusion of DG did not affect dry matter intake (P=0.35) but a trend for an increase in milk yield was observed (P=0. 10). Additionally, the percentages of milk fat and protein in the milk were not affected (P=0.24 and 0.25, respectively). The modeled daily rumen outflow of Lys in grams was significantly (P<0.01) reduced and Met was not affected (P=0.79) when DG were included. The error associated with net energy of lactation allowable milk averaged 5.0±1.0 kg d−1and was not affected by DG (P=0.79) but the error associated with metabolizable protein allowable milk tended (P=0.10) to be higher for cows consuming DG by 1.4±1.2 kg d−1.

Lignin: characterization of a multifaceted crop component

Lignin is a plant component with important implications for various agricultural disciplines. It confers rigidity to cell walls, and is therefore associated with tolerance to abiotic and biotic stresses and the mechanical stability of plants. In animal nutrition, lignin is considered an antinutritive component of forages as it cannot be readily fermented by rumen microbes. In terms of energy yield from biomass, the role of lignin depends on the conversion process. It contains more gross energy than other cell wall components and therefore confers enhanced heat value in thermochemical processes such as direct combustion. Conversely, it negatively affects biological energy conversion processes such as bioethanol or biogas production, as it inhibits microbial fermentation of the cell wall. Lignin from crop residues plays an important role in the soil organic carbon cycling, as it constitutes a recalcitrant carbon pool affecting nutrient mineralization and carbon sequestration. Due to the significance of lignin in several agricultural disciplines, the modification of lignin content and composition by breeding is becoming increasingly important. Both mapping of quantitative trait loci and transgenic approaches have been adopted to modify lignin in crops. However, breeding goals must be defined considering the conflicting role of lignin in different agricultural disciplines.

Acute colic possibly caused by phytobezoar derived from napier grass in 5 Japanese black cows reared in the same farm

For 6 years, 5 Japanese Black cows of the same herd showed anorexia, depression, and dehydration with no feces in the rectum. Biomedical examination of 3 animals showed severe hypokalemia and hypochloremia. Although the first 3 animals died or were slaughtered (causes unknown), necropsy results showed that the cow in case 4 had intestinal obstruction due to phytobezoar derived from napier grass, fed mainly to the cattle as roughage. Therefore, farmers were recommended to avoid the hard root-stem portion of napier grass as roughage. Consequently, less phytobezoar was recovered from the fifth cow, and no similar clinical case of intestinal obstruction was observed thereafter. This is the first report on intestinal obstruction caused by phytobezoars derived from napier grass.

Nutritive value of some herbage for dromedary camels in the central arid zone of Iran

The purpose of this study is to prepare standard tables of the chemical composition of feedstuff and to determine the digestibility and palatability of different plant species in the dromedary camel, this research was conducted considering the consumed herbages by camels in the central arid zone of Iran. The following plant species were included: Alhagi camelorum, Artemisia sieberi, Atriplex lentiformis, Haloxylon persicum, Hammada salicornica, Salsola tomentosa, Salsola rigida, Seidlitzia rosmarinus, Suaeda fruticosa, Tamarix tree, and Tamarix kotschi. Thirty samples of the browsing parts were collected from three sites in the rangelands of Qom and Yazd province. The chemical composition of the samples, including dry matter, crude protein (CP), crude fiber, neutral detergent fiber (NDF), acid detergent fiber (ADF), ether extract, total ash, macroelements (Ca, P, Mg, K), microelements, and gross energy were measured. The in vitro digestibility of the plants was measured by camel liquor using the Tilley and Terry method. The palatability of the plants was measured by four mature camels in cafeteria trials. Data were analyzed by general linear model method using the SAS software. The highest CP (17.5%) related to Haloxylon persicum and the lowest NDF (26.2%) and ADF (12.6%) were related to Salsola rigida. The lowest CP (5.5%) and the highest NDF (72.8%) and ADF (59.6%) were related to Artemisia sieberi. The results also indicate that Atriplex lentiformis, Alhagi camelorum, Seidlitzia rosmarinus, Suaeda fruticosa, Haloxylon persicum, Salsola tomentosa, Hammada salicornica, T. kotschi, Salsola rigida, Tamarix tree, and Artemisia seiberi were more pleasurable feeds, respectively. There was no consistent relationship between the palatability of herbages with the percentage of digestible organic matter in the dry matter or chemical composition.

Variability in in situ ruminal degradation parameters causes imprecision in estimated ruminal digestibility

The ruminal digestibility of dietary ingredients is frequently estimated with degradation parameters (e.g., rate and extent of degradation). Mean degradation parameters (e.g., those in a feed library) are often used, but limited data suggest considerable variation around these means, potentially leading to imprecise digestibility estimates. This experiment quantified degradation parameter variation for forage hays and determined the impact of this variation on the precision of ruminal digestibility estimates. Degradation data were those previously published by our laboratory and included degradation rate, lambda(d) (h(-1)), fraction instantly degraded, a (g x g(-1)), potential extent of degradation, (a + b) (g x g(-1)), and fraction not instantly degraded that is potentially degradable, b (g x g(-1)) of alfalfa, grass, and grass-legume hays. Ruminal digestibilities of chemical fractions (dry matter, neutral detergent fiber, acid detergent fiber, hemicellulose, crude protein) were estimated using these data. Ninety-five percent confidence limits of digestibility were determined using propagation of uncertainty with measured standard deviations of degradation parameters. Values for coefficients of variation of degradation parameters were large; averaged across chemical fractions, they were 24.8, 28.6, 20.7, and 12.6% for lambda(d), a, b, and (a + b). Ninety-five percent confidence limits of digestibility were large (80.5% of digestibility means) and often overlapped each other, even when digestibility means differed greatly numerically. Consequently, digestibility values computed with mean degradation parameters may have little biological and practical significance. When uncertainty in all parameters but lambda(d) was set to zero (lambda(d) alone had uncertainty), 95% confidence limits still encompassed 54.5% of digestibility means. Thus, uncertainty in lambda(d) alone caused considerable imprecision in estimated digestibility. These results caution against using mean degradation parameters to estimate digestibility.

The effect of a condensed tannin-containing forage on methane emission by goats

The objective of this study was to compare methane emission by goats consuming the condensed tannin-containing forage sericea lespedeza (Les-pedeza cuneata) or a mixture of crabgrass (Digitaria ischaemum) and Kentucky 31 tall fescue (Festuca arundinacea). Two groups of 12 Angora does (initial average BW = 41.5 +/- 2.7 kg) that previously grazed a pasture of sericea lespedeza or crabgrass/tall fescue for approximately 4 mo were used. After 1 wk of adaptation to metabolism cages, gas exchange was measured for 24 h in an open-circuit respiration calorimetry system with four head boxes. Forage harvested daily from the previously grazed pastures was consumed ad libitum. Crude protein concentration was 10.3 and 13.0%, IVDMD was 64.5 and 75.3%, and the level of condensed tannins was 17.7 and 0.5% for sericea lespedeza and crabgrass/tall fescue, respectively. Dry matter intake (1.11 vs. 0.67 kg/d) and digestible DMI (estimated from IVDMD; 0.71 vs. 0.51 kg/d) were greater (P < 0.01) for sericea lespedeza than for crabgrass/tall fescue. Ruminal ammonia N (3.7 and 9.9 mg/dL; P < 0.001) and plasma urea-N concentrations (16.7 and 20.9 mg/dL; P = 0.07) were lower for sericea lespedeza than for crabgrass/tall fescue. Concentrations of individual and total VFA and the acetate-to-propionate ratio in ruminal fluid did not differ between treatments (P > 0.19). Despite higher DMI by goats fed sericea lespedeza, daily energy expenditure (409 vs. 431 kJ/kg BW(0.75)), heart rate (70 vs. 73 beats/min), and the ratio of energy expenditure to heart rate (5.82 vs. 5.94) did not differ between sericea lespedeza and crabgrass/tall fescue, respectively (P > 0.13). Methane emission expressed as both quantity per day or relative to DMI was lower (P <0.001) for sericea lespedeza than for crabgrass/tall fescue (7.4 vs. 10.6 g/d and 6.9 vs. 16.2 g/kg DMI). Substantial differences between the forages in condensed tannins concentration and methane emission by Angora goats suggest that condensed tannins decreased methane emission.

Nutritive value of some herbages for dromedary camel in Iran

To prepare standard tables of chemical composition of feedstuffs and to determine digestibility and palatability of different plant species in dromedary camel, this research was carried out by considering the most consuming herbages of Iranian desert rages. The plant species were included Atriplex lentiformis, Alhagi persarum, Seidlitzia rosmarinus, Saueda fruticosa, Haloxylon ammodendron, Tamarix kotschyi, Hammada salicornica, Salsola yazdiana, Salsola tomentosa, Tamarix aphylla and Artemisia sieberi. Thirty samples of the browsing parts were collected from the rangelands of Yazd province in autumn. Chemical composition of samples including Dry Matter (DM), Crude Protein (CP), Crude Fiber (CF), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Ether Extract (EE), Total Ash (TA), macro elements (Ca, P, Mg, K), micro elements (Fe, Mg, Cu, Zn)and gross energy (GE) were analyzed. The in vitro digestibility was determined by camel rumen liquor in Tilley and Terry method. Palatability of the plants were measured by three mature camels in cafeteria trials. The camels voluntarily fed 11 plant species during one hour for six days. Data were analyzed by GLM method in SAS software. The highest CP (18.3%) and the lowest NDF (40.4%) and ADF (35.4%) were related to Tamarix aphylla. The lowest CP (5.5%) and the highest NDF (72.8%) and ADF (59.6%) were related to Artemisia sieberi. The highest organic matter digestibility in dry matter was related to Haloxylon ammodendron. The results also indicated that Atriplex lentiformis, Alhagi persarum, Seidlitzia rosmarinus, Saueda fruticosa, Haloxylon ammodendron, Salsola tomentosa, Hammada salicornica, Tamarix kotschyi, Salsola yazdiana, Tamarix aphylla and Artemisia sieberi were more pleasure feed, respectively. It was not observed any correlation between %DOMD and chemical composition. Moreover, There was not a consistent relationship between the palatability of herbages with %DOMD or chemical composition.

Comparison of the acetyl bromide spectrophotometric method with other analytical lignin methods for determining lignin concentration in forage samples

Present analytical methods to quantify lignin in herbaceous plants are not totally satisfactory. A spectrophotometric method, acetyl bromide soluble lignin (ABSL), has been employed to determine lignin concentration in a range of plant materials. In this work, lignin extracted with acidic dioxane was used to develop standard curves and to calculate the derived linear regression equation (slope equals absorptivity value or extinction coefficient) for determining the lignin concentration of respective cell wall samples. This procedure yielded lignin values that were different from those obtained with Klason lignin, acid detergent acid insoluble lignin, or permanganate lignin procedures. Correlations with in vitro dry matter or cell wall digestibility of samples were highest with data from the spectrophotometric technique. The ABSL method employing as standard lignin extracted with acidic dioxane has the potential to be employed as an analytical method to determine lignin concentration in a range of forage materials. It may be useful in developing a quick and easy method to predict in vitro digestibility on the basis of the total lignin content of a sample.

A mechanistic model for predicting the nutrient requirements and feed biological values for sheep1

The Cornell Net Carbohydrate and Protein System (CNCPS), a mechanistic model that predicts nutrient requirements and biological values of feeds for cattle, was modified for use with sheep. Published equations were added for predicting the energy and protein requirements of sheep, with a special emphasis on dairy sheep, whose specific needs are not considered by most sheep-feeding systems. The CNCPS for cattle equations that are used to predict the supply of nutrients from each feed were modified to include new solid and liquid ruminal passage rates for sheep, and revised equations were inserted to predict metabolic fecal N. Equations were added to predict fluxes in body energy and protein reserves from BW and condition score. When evaluated with data from seven published studies (19 treatments), for which the CNCPS for sheep predicted positive ruminal N balance, the CNCPS for sheep predicted OM digestibility, which is used to predict feed ME values, with no mean bias (1.1 g/100 g of OM; P > 0.10) and a low root mean squared prediction error (RMSPE; 3.6 g/100 g of OM). Crude protein digestibility, which is used to predict N excretion, was evaluated with eight published studies (23 treatments). The model predicted CP digestibility with no mean bias (-1.9 g/100 g of CP; P > 0.10) but with a large RMSPE (7.2 g/100 g of CP). Evaluation with a data set of published studies in which the CNCPS for sheep predicted negative ruminal N balance indicated that the model tended to underpredict OM digestibility (mean bias of -3.3 g/100 g of OM, P > 0.10; RMSPE = 6.5 g/100 g of OM; n = 12) and to overpredict CP digestibility (mean bias of 2.7 g/100 g of CP, P > 0.10; RMSPE = 12.8 g/100 g of CP; n = 7). The ability of the CNCPS for sheep to predict gains and losses in shrunk BW was evaluated using data from six studies with adult sheep (13 treatments with lactating ewes and 16 with dry ewes). It accurately predicted variations in shrunk BW when diets had positive N balance (mean bias of 5.8 g/d; P > 0.10; RMSPE of 30.0 g/d; n = 15), whereas it markedly overpredicted the variations in shrunk BW when ruminal balance was negative (mean bias of 53.4 g/d, P < 0.05; RMSPE = 84.1 g/d; n = 14). These evaluations indicated that the Cornell Net Carbohydrate and Protein System for Sheep can be used to predict energy and protein requirements, feed biological values, and BW gains and losses in adult sheep.

Corn Silage Management: Effects of Hybrid, Maturity, Chop Length, and Mechanical Processing on Rate and Extent of Digestion

Five experiments were conducted to evaluate the effects of hybrid, chop length, maturity, and mechanical processing of corn silage on dry matter and nutrient disappearance in the rumen. Corn silage that had not been dried or ground was incubated in macro in situ bags (30 x 35 cm) for 8, 16, 24,48, and 96 h. Experiments la and 2 evaluated the effects of maturity and mechanical processing for two corn silage hybrids harvested at two theoretical lengths-of-cut. Experiments 3 through 5 evaluated the effects of chop length and mechanical processing for two corn silage hybrids harvested at two-thirds milkline. The hybrid with low neutral fiber (NDF) concentrations had greater dry matter and starch disappearance than the hybrid with high NDF concentrations. The effect of chop length on nutrient disappearance was variable across experiments 3 through 5. Processing improved dry matter disappearance in experiments la, 2 (two-thirds milkline and blackline), 3, 4, and 5 at the majority of ruminal incubation timepoints. Starch disappearance was greater for unprocessed corn silage in experiment la (hard dough and two-thirds milkline) and was greater for processed corn silage in experiments 2 and 5. However, there was no consistent trend in starch disappearance between processed and unprocessed corn silage in experiments 3 and 4. This can be partially explained by the high disappearance of starch (experiment 3, > or = 98% and experiment 4, > or = 94%) by 24 h of ruminal incubation. Minimal differences were detected in NDF disappearance between processed and unprocessed corn silage across maturities. In experiments 2 and 5, crude protein disappearance was improved due to processing at some incubation timepoints. Rate of dry matter, starch (one-third milkline and two-thirds milkline), and NDF disappearance tended to increase when corn silage was mechanically processed in experiment 2. Dry matter, starch, and crude protein disappearance tended to be greater for corn silage harvested at the early maturity (one-third milkline) in experiment 2 compared with advanced maturities (two-thirds milkline and blackline). Disappearance of NDF was greater at early maturities compared with advanced maturities in experiments 1a and 2. Rate of dry matter (hybrid 3845), starch, and NDF (hybrid 3845) disappearance tended to decrease as maturity advanced from one-third milkline to blackline in experiment 2. These results suggest that the macro in situ method can be used to evaluate nutrient disappearance in the rumen.

Evaluation of tropical grasses for milk production by dual-purpose cows in tropical Mexico

Two experiments using the Cornell Net Carbohydrate and Protein System were conducted to characterize the carbohydrate and protein fractions and corresponding rates of digestion of 15 tropical pasture grasses and to evaluate their ability to support milk production by dual-purpose cows. In the first experiment, ranges in carbohydrate and protein fractions of 15 grasses at 35 to 42 d of regrowth were: neutral detergent fiber (NDF) 63.5 to 74.9% of DM; permanganate lignin 4.7 to 7.8% of NDF; CP 5.5 to 11.9% of DM; and soluble protein 15.1 to 44.1% of crude protein (CP). The ranges of rates of digestion expressed as percent per hour were neutral detergent solubles (7.5 to 27.4); NDF (3.8 to 8.4); and neutral detergent insoluble protein (2.9 to 9.5). Predictions of the amount of milk that could be produced based on the amount of metabolizable energy supplied by the diet decreased 35% when NDF increased from 60 to 80%, and increased 88% when the rate of digestion of NDF increased from 3 to 6%/h. The milk production that could be sustained based on metabolizable protein in the diet doubled as CP increased from 4 to 12%. In the second experiment, nitrogen fertilization reduced NDF 7.3% and increased CP 84% without changing protein solubility, resulting in increased rumen nitrogen and metabolizable protein balances. With all forages, the Cornell Net Carbohydrate and Protein System predicted that availability of metabolizable protein would limit milk production. Predicted microbial growth was limited by ruminally available protein rather than by available carbohydrate.