L.E. Chase

Characteristics of neutral detergent-soluble fiber fermentation by mixed ruminal microbes

Abstract A new method for determining neutral detergent-soluble fiber (NDSF) estimates the non-starch polysaccharide present in 90% ethanol-insoluble residue (EIR) but absent from neutral detergent residue (NDF). Unextracted feeds, EIR and NDF of feeds high in pectic substances were fermented in vitro with mixed ruminal microbes and gas production was measured. Soybean hulls were fermented for 48 h, and all other feeds for 24 h. Fermentation kinetics of NDSF were determined from gas curves produced by point by point subtraction of the gas production curves of NDF from those of EIR. Single-pool logistic fermentation rates and lag times for NDSF and NDF were determined from the gas production data. The single-pool logistic rates for NDSF for dried citrus pulp, dried beet pulp, soybean hulls, mature alfalfa stems and leaves and immature alfalfa stems and leaves were 0.13, 0.16, 0.05, 0.11, 0.14, 0.18 and 0.13 h −1 , respectively. Fermentation rates tended to be faster and lag times shorter for NDSF than for NDF. Acetate to propionate ratios were numerically higher for EIR fermentations than for unextracted feeds or NDF. The fermentation characteristics of NDSF for the feeds in this study are consistent with reports of pectic substance fermentations indicating that NDSF does describe the soluble fiber fraction. The NDSF and gas production measurement methods offer nutritionally relevant ways to estimate soluble fiber content and its digestion characteristics in feedstuffs.

The Cornell Net Carbohydrate and Protein System: Updates to the model and evaluation of version 6.5

New laboratory and animal sampling methods and data have been generated over the last 10 yr that had the potential to improve the predictions for energy, protein, and AA supply and requirements in the Cornell Net Carbohydrate and Protein System (CNCPS). The objectives of this study were to describe updates to the CNCPS and evaluate model performance against both literature and on-farm data. The changes to the feed library were significant and are reported in a separate manuscript. Degradation rates of protein and carbohydrate fractions were adjusted according to new fractionation schemes, and corresponding changes to equations used to calculate rumen outflows and postrumen digestion were presented. In response to the feed-library changes and an increased supply of essential AA because of updated contents of AA, a combined efficiency of use was adopted in place of separate calculations for maintenance and lactation to better represent the biology of the cow. Four different data sets were developed to evaluate Lys and Met requirements, rumen N balance, and milk yield predictions. In total 99 peer-reviewed studies with 389 treatments and 15 regional farms with 50 different diets were included. The broken-line model with plateau was used to identify the concentration of Lys and Met that maximizes milk protein yield and content. Results suggested concentrations of 7.00 and 2.60% of metabolizable protein (MP) for Lys and Met, respectively, for maximal protein yield and 6.77 and 2.85% of MP for Lys and Met, respectively, for maximal protein content. Updated AA concentrations were numerically higher for Lys and 11 to 18% higher for Met compared with CNCPS v6.0, and this is attributed to the increased content of Met and Lys in feeds that were previously incorrectly analyzed and described. The prediction of postruminal flows of N and milk yield were evaluated using the correlation coefficient from the BLUP (R(2)BLUP) procedure or model predictions (R(2)MDP) and the concordance correlation coefficient. The accuracy and precision of rumen-degradable N and undegradable N and bacterial N flows were improved with reduced bias. The CNCPS v6.5 predicted accurate and precise milk yield according to the first-limiting nutrient (MP or metabolizable energy) with a R(2)BLUP=0.97, R(2)MDP=0.78, and concordance correlation coefficient=0.83. Furthermore, MP-allowable milk was predicted with greater precision than metabolizable energy-allowable milk (R(2)MDP=0.82 and 0.76, respectively, for MP and metabolizable energy). Results suggest a significant improvement of the model, especially under conditions of MP limitation.

Updating the Cornell Net Carbohydrate and Protein System feed library and analyzing model sensitivity to feed inputs

The Cornell Net Carbohydrate and Protein System (CNCPS) is a nutritional model that evaluates the environmental and nutritional resources available in an animal production system and enables the formulation of diets that closely match the predicted animal requirements. The model includes a library of approximately 800 different ingredients that provide the platform for describing the chemical composition of the diet to be formulated. Each feed in the feed library was evaluated against data from 2 commercial laboratories and updated when required to enable more precise predictions of dietary energy and protein supply. A multistep approach was developed to predict uncertain values using linear regression, matrix regression, and optimization. The approach provided an efficient and repeatable way of evaluating and refining the composition of a large number of different feeds against commercially generated data similar to that used by CNCPS users on a daily basis. The protein A fraction in the CNCPS, formerly classified as nonprotein nitrogen, was reclassified to ammonia for ease and availability of analysis and to provide a better prediction of the contribution of metabolizable protein from free AA and small peptides. Amino acid profiles were updated using contemporary data sets and now represent the profile of AA in the whole feed rather than the insoluble residue. Model sensitivity to variation in feed library inputs was investigated using Monte Carlo simulation. Results showed the prediction of metabolizable energy was most sensitive to variation in feed chemistry and fractionation, whereas predictions of metabolizable protein were most sensitive to variation in digestion rates. Regular laboratory analysis of samples taken on-farm remains the recommended approach to characterizing the chemical components of feeds in a ration. However, updates to the CNCPS feed library provide a database of ingredients that are consistent with current feed chemistry information and laboratory methods and can be used as a platform to formulate rations and improve the description of biology within the model.

Development and evaluation of equations in the Cornell Net Carbohydrate and Protein System to predict nitrogen excretion in lactating dairy cows.

Nitrogen excretion is of particular concern on dairy farms, not only because of its effects on water quality, but also because of the subsequent release of gases such as ammonia to the atmosphere. To manage N excretion, accurate estimates of urinary N (UN) and fecal N (FN) are needed. On commercial farms, directly measuring UN and FN is impractical, meaning that quantification must be based on predictions rather than measured data. The purpose of this study was to use a statistical approach to develop equations and evaluate the Cornell Net Carbohydrate and Protein Systems (CNCPS) ability to predict N excretion in lactating dairy cows, and to compare CNCPS predictions to other equations in the literature. Urinary N was over-predicted by the CNCPS due to inconsistencies in N accounting within the model that partitioned more N to feces than urine, although predicted total N excretion was reasonable. Data to refine model predictions were compiled from published studies (n=32) that reported total collection N balance results. Considerable care was taken to ensure the data included in the development data set (n=104) accounted for >90% of the N intake (NI). Unaccounted N for the compiled data set was 1.47±4.60% (mean ± SD). The results showed that FN predictions could be improved by using a modification of a previously published equation: FN (g/d) = [[NI (g/kg of organic matter) × (1 - 0.842)] + 4.3 × organic matter intake (kg/d)] × 1.20, which, when evaluated against the compiled N balance data, had a squared coefficient of determination based on a mean study effect R(MP)(2) of 0.73, concurrent correlation coefficient (CCC) of 0.83 and a root mean square error (RMSE) of 10.38 g/d. Urinary N is calculated in the CNCPS as the difference between NI and other N excretion and losses. Incorporating the more accurate FN prediction into the current CNCPS framework and correcting an internal calculation error considerably improved UN predictions (RMSE=12.73 g/d, R(MP)(2)=0.86, CCC=0.90). The changes to FN and UN translated into an improved prediction of total manure N excretion (RMSE=12.42 g/d, R(MP)(2)=0.96, CCC=0.97) and allows nutritionists and farm advisors to evaluate these factors during the ration formulation process.

Optimal dairy farm adjustments to increased utilization of corn distillers dried grains with solubles.

The purpose of this paper was to identify effective dairy farm management adjustments related to recent structural changes in agricultural commodity markets because of expanded biofuels production and other market factors. We developed a mathematical programming model of a representative dairy farm in New York State to estimate the effects of changes in the relative prices of important feed components on farm profitability, identify optimal adjustments for on-farm feed production, crop sales, and dairy rations that account for expanded utilization of corn distillers dried grains with solubles (DDGS), and point out potential implications of these adjustments on whole-farm nutrient planning. We mapped out an effective farm-level demand curve for DDGS by varying DDGS prices relative to other primary feed ingredients, which allowed us to compare DDGS utilization at alternative market conditions. Had the relative prices of major feed ingredients remained at their historical averages, our results suggest that there is only modest potential for feeding DDGS through supplementation in rations for dry cows and heifers as a substitute for soybean meal. However, the relatively lower DDGS prices experienced in 2008 imply an expanded optimal use of DDGS to include rations for lactating cows at 10% of the total mixed ration. Despite these expanded opportunities for DDGS at lower prices, the effects on farm net returns were modest. The most important considerations are perhaps those related to changes in the phosphorus (P) levels in the dairy waste. We showed that including moderate levels of DDGS (10%) in rations for lactating cows did not significantly increase P excretion. However, if the rations for dry cows and heifers were supplemented with DDGS, P excretion did increase, resulting in sizable increases of plant-available phosphorus applied to cropland well beyond crop nutrient requirements. Although our results show that it is economically optimal for the dairy producer to incorporate DDGS into these rations, some operations will be unable to accommodate the additional P because of existing nutrient management recommendations, soil P status, and the number of acres available for manure spreading.

Responses of late-lactation cows to forage substitutes in low-forage diets supplemented with by-products1

In response to drought-induced forage shortages along with increased corn and soy prices, this study was conducted to evaluate lactation responses of dairy cows to lower-forage diets supplemented with forage substitutes. By-product feeds were used to completely replace corn grain and soybean feeds. Forty-eight late-lactation cows were assigned to 1 of 4 diets using a randomized complete block design with a 2-wk covariate period followed by a 4-wk experimental period. The covariate diet contained corn grain, soybean meal, and 61% forage. Experimental diets contained chopped wheat straw (WS)/sugar beet pulp at 0/12, 3/9, 6/6, or 9/3 percentages of diet dry matter (DM). Corn silage (20%), alfalfa silage (20%), pelleted corn gluten feed (25.5%), distillers grains (8%), whole cottonseed (5%), cane molasses/whey blend (7%), and vitamin and mineral mix with monensin (2.5%) comprised the rest of diet DM. The WS/sugar beet pulp diets averaged 16.5% crude protein, 35% neutral detergent fiber, and 11% starch (DM basis). Cows consuming the experimental diets maintained a 3.5% fat- and protein-corrected milk production (35.2 kg; standard deviation=5.6 kg) that was numerically similar to that measured in the covariate period (35.3 kg; standard deviation=5.0 kg). Intakes of DM and crude protein declined linearly as WS increased, whereas neutral detergent fiber intake increased linearly. Linear increases in time spent ruminating (from 409 to 502 min/d) and eating (from 156 to 223 min/d) were noted as WS inclusion increased. Yields of milk fat and 3.5% fat-and protein-corrected milk did not change as WS increased, but those of protein and lactose declined linearly. Phosphorous intakes were in excess of recommended levels and decreased linearly with increasing WS inclusion. Nutritional model predictions for multiparous cows were closest to actual performance for the National Research Council 2001 model when a metabolizable protein basis was used; primiparous cow performance was better predicted by energy-based predictions made with the National Research Council or Cornell Net Carbohydrate and Protein System models. Model predictions of performance showed a quadratic diet effect with increasing WS. Lactating dairy cows maintained production on low-forage diets that included forage substitutes, and in which by-product feeds fully replaced corn grain and soybean. However, longer-term studies are needed to evaluate animal performance and to improve model predictions of performance on these nontraditional diets.

Brown midrib corn silage fed during the peripartal period increased intake and resulted in a persistent increase in milk solids yield of Holstein cows

The objective of this study was to evaluate transition cow performance when brown midrib corn silage (BMRCS; Mycogen F2F444) was included in the diet during the transition period, and to determine if any production response occurring during the first 3 wk of lactation would persist from wk 4 to 15 when a common diet was fed. Seventy Holstein dairy cows were blocked by parity (either second or third and greater) and calving date and randomly assigned to the CCS (a mixture of varieties of conventional corn silage) or BMRCS treatment. Diets were formulated with the objective of keeping all ration parameters the same, with the exception of neutral detergent fiber digestibility. Neutral detergent fiber digestibility values (30 h) for CCS and BMRCS averaged 56.8 and 73.8%, respectively. Prepartum rations contained 47% corn silage, 18% wheat straw, 7% alfalfa haylage, and 28% concentrate, and averaged 45% neutral detergent fiber (DM basis). Postpartum rations contained 40% corn silage, 15% alfalfa haylage, 1% straw, and 44% concentrate. Milk weights (3×/d) and dry matter intake were recorded daily, and milk composition was measured weekly. Cows fed BMRCS had higher dry matter intake during the 2-wk period before calving (14.3 vs. 13.2 kg/d) and the 3-wk period after calving (20.1 vs. 18.1 kg/d) than did cows fed CCS. Yields of milk, solids, and lactose were increased, whereas a trend was observed for a reduction in somatic cell counts and linear scores in the postpartum period for cows receiving BMRCS during the transition. A significant carryover effect of BMRCS was observed on production from wk 4 to 15 when the common diet was fed, with yields of protein (1.36 vs. 1.30 kg/d), lactose (2.24 vs. 2.12 kg/d), and solids (5.82 vs. 5.51 kg/d) increasing significantly, and yields of fat-corrected milk, energy-corrected milk, and fat tending to increase during this period for cows that had been fed BMRCS. The increased intakes during the last 2 wk of the prepartum period in the BMRCS treatment were likely because of a reduction in fill, whereas the increased intakes in the postpartum period in cows fed the BMRCS were either because of the higher intakes during the prepartum period or because of a reduction in fill limitations in the postpartum period. The carryover response in wk 4 to 15 may have resulted from cows that received BMRCS during the transition period being in a more positive nutrient balance than cows fed CCS. The results of this study indicate the importance that digestible NDF can have in transition diets and the long-term production responses that can occur when intake is increased in the transition period.

Nitrogen balances for New York State: Implications for manure and fertilizer management

New York (NY) has dairy, cash grain, fruit, and vegetable industries located in close proximity to water, making it important to optimize manure and fertilizer use for both economic production of crops and protection of the environment. The gross phosphorus (P) balance for NY (manure and fertilizer P minus crop P removal) estimated for 2006 was +1.7 kg ha−1 (+1.5 lb ac−1), indicating that, on a statewide basis, P is in balance. Our objectives in this study were to (1) estimate state, regional, and county-level gross nitrogen (N) balances for NY for 2007; (2) evaluate N balance trends over time (1987, 1992, 1997, 2002, and 2007); (3) estimate nonlegume cropland (net) N balances for 2007; and (4) quantify the potential impact of improved herd nutrition and manure incorporation on N balances. The 2007 NY gross N balance for nonlegume cropland was +62 kg ha−1 (+55 lb ac−1). Long Island and western NY had the highest N balances (+101 and +77 kg ha−1 [+90 and +69 lb ac−1], respectively) reflecting N fertilizer use for horticultural and/or cash grain crops (both regions) and presence of a concentrated dairy industry (western NY). The Chesapeake Bay watershed and Lake Champlain Basin counties had gross N balances below +28 kg ha−1 (+25 lb ac−1). The statewide N balance decreased from +125 kg ha−1 (+112 lb ac−1) in 1987 to +62 kg ha−1 (+55 lb ac−1) in 2007, largely driven by a decline in N fertilizer use between 1987 and 1992. The statewide N balance dropped to −38 kg ha−1 (−34 lb ac−1) when manure N losses in the barn and storage system and at land application were taken into account. Given a nearly zero P balance, a negative N balance indicates the need for best management practices that increase N use efficiency of manure and fertilizer and/or add N from other sources (cover crops, greater reliance on N fixation, shorter rotations). Improvement in herd nutrition through precision feeding has the potential to increase N use efficiency of surface applied manure and thus reduce N loss to the environment. However, such improvements will also reduce the total amount of N excreted and decrease the N:P ratio of the manure. Best management practices that reduce N loss in the barn and storage system, increase manure and fertilizer N uptake efficiency, and/or reduce N needs will be essential in order to balance N and P for the long-term sustainability of NY agriculture.

A fecal test for assessing phosphorus overfeeding on dairy farms: evaluation using extensive farm data.

Managing P on dairy farms requires the assessment and monitoring of P status of the animals so that potential overfeeding may be minimized. Numerous published studies have demonstrated that for lactating dairy cows, increasing P concentrations in diets led to greater P excretion in feces. More recent work reported that inorganic P (P(i)) in 0.1% HCl extracts of feces (fecal extract P(i), g/kg) closely reflects dietary P changes. This has led to the proposal that 0.1% HCl fecal extract P(i) may serve as an indicator of the animals P status (adequate or excessive) when compared with a benchmark value. Here, we present the results of an extensive evaluation of the proposed fecal P indicator test. With samples (n=575) from >90 farms, fecal total P (TP, g/kg) and fecal extract P were positively correlated with dietary P (X, g/kg): TP=1.92X - 0.17 (R2=0.36); fecal extract P=1.82X - 2.54 (R2=0.46). Fecal extract P was responsive to dietary P changes, whereas the remaining P, calculated as TP minus fecal extract P, was not. A provisional benchmark value of fecal extract P representing near-adequate P status was set at 4.75g/kg. Assessment of the farm data using the benchmark indicated that 316 out of 575 data points were associated with possible P overfeeding. Advantages of the fecal-based test over feed-based analysis to assess P status are discussed. The fecal extract P method is a simple and practical test that can be used as an assessment tool for helping dairy producers improve P management and reduce their environmental footprint.

Effect of lignin linkages with other plant cell wall components on in vitro and in vivo neutral detergent fiber digestibility and rate of digestion of grass forages

The objective of this study was to correlate in vitro and in vivo neutral detergent fiber (NDF) digestibility (NDFD) with the chemical composition of forages and specific chemical linkages, primarily ester- and ether-linked para-coumaric (pCA) and ferulic acids (FA) in forages fed to dairy cattle. The content of acid detergent lignin (ADL) and its relationship with NDF does not fully explain the observed variability in NDFD. The ferulic and p-coumaric acid linkages between ADL and cell wall polysaccharides, rather than the amount of ADL, might be a better predictor of NDFD. Twenty-three forages, including conventional and brown midrib corn silages and grasses at various stages of maturity were incubated in vitro for measurement of 24-h and 96-h NDFD. Undigested and digested residues were analyzed for NDF, acid detergent fiber (ADF), ADL, and Klason lignin (KL); ester- and ether-linked pCA and FA were determined in these fractions. To determine whether in vitro observations of ester- and ether-linked pCA and FA and digestibility were similar to in vivo observations, 3 corn silages selected for digestibility were fed to 6 ruminally fistulated cows for 3 wk in 3 iso-NDF diets. Intact samples and NDF and ADF residues of diet, rumen, and feces were analyzed for ester- and ether-linked pCA and FA. From the in vitro study, the phenolic acid content (total pCA and FA) was highest for corn silages, and overall the content of ester- and ether-linked pCA and FA in both NDF and ADF residues were correlated with NDF digestibility parameters, reflecting the competitive effect of these linkages on digestibility. Also, Klason lignin and ADL were negatively correlated with ether-linked ferulic acid on an NDF basis. Overall, esterified FA and esterified pCA were negatively correlated with all of the measured fiber fractions on both a dry matter and an NDF basis. The lignin content of the plant residues and chemical linkages explained most of the variation in both rate and extent of NDF digestion but not uniformly among forages, ranging from 56 to 99%. The results from the in vivo study were similar to the in vitro data, demonstrating the highest total-tract aNDF digestibility (70%; NDF analysis conducted with α-amylase and sodium sulfite) for cows fed the corn silage with the lowest ester- and ether-linked pCA content in the NDF fraction. In this study, digestibility of forage fiber was influenced by the linkages among lignin and the carbohydrate moieties, which vary by hybrid and species and most likely vary by the agronomic conditions under which the plant was grown.