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Adjust dietary starch throughout lactation

Adjust dietary starch throughout lactation
The concentration and ruminal digestibility of starch in rations for lactating cows have important effects on dairy cow productivity

*Dr. Mike Allen is a university distinguished professor in the Michigan State University department of animal science. He presented this paper at the 2012 Four-State Dairy Nutrition & Management Conference.

STARCH is a highly digestible and energy-dense feed component that typically ranges from less than 20% to greater than 28% inclusion in rations fed to lactating dairy cows.

Forages are supplemented with cereal grains to increase energy density, provide glucose precursors and decrease the filling effects of rations.

Starch is composed of polymers of glucose (amylose and amylopectin) with bonds that are readily cleaved by mammalian enzymes. However, starch is packaged in granules that are embedded in a protein matrix in the seed endosperm, which varies in solubility and resistance to digestion (Kotarski et al., 1992).

These differences in endosperm type have great effects on ruminal fermentability of starch, which ranges widely --  from less than 30% to more than 90% -- depending on the cereal grain (Nocek and Tamminga, 1991; Firkins et al., 2001). Altering the concentration and ruminal fermentability of starch in rations affects the digestibility of starch (Ngonyamo-Majee et al., 2008), ruminal pH and fiber digestibility (Firkins et al., 2001) and the type, amount and temporal absorption of fuels (e.g., acetate, propionate, lactate, glucose) available to the cow (Allen, 2000).

This has great effects on lactational performance by affecting energy intake and partitioning as well as absorbed protein (Allen et al., 2009). In addition, effects on animal performance depend on the physiological state of the cows, which varies greatly throughout lactation (Allen et al., 2005).

Therefore, the optimal concentration and ruminal fermentability of starch in rations of lactating cows vary throughout lactation. The objective of this article is to discuss what determines the site of digestion and total tract digestibility of starch, how the concentration and ruminal fermentability of starch affect animal performance and considerations related to starch when formulating diets for lactating dairy cows.


Starch fermentability

Ruminal fermentability of starch is highly variable and affected by grain type, vitreousness, processing (e.g., rolling, grinding, steam flaking), conservation method (dry or ensiled), ration composition and animal characteristics.

Starch in wheat, barley and oats is generally more readily fermented than starch in corn, and starch in sorghum is most resistant to fermentation in the rumen and digestion by the animal (Huntington, 1997).

These differences are largely because of differences in endosperm type rather than differences in starch composition (amylose versus amylopectin), per se. Floury endosperm contains proteins that are readily solubilized, allowing enzymes greater access to starch granules, while vitreous endosperm contains prolamin proteins that are insoluble and resistant to digestion, decreasing enzymes' access to starch granules (Hoffman and Shaver, 2010).

Starch sources vary in the amount and proportion of the two types of endosperm, and there is a large variation in vitreousness of the endosperm (percentage of the total endosperm that is vitreous) among varieties within certain grain type. Endosperm vitreousness in corn harvested dry ranges from 0% to greater than 75%, and corn with more vitreous endosperm is more resistant to both particle size reduction by grinding and digestion (Hoffman et al., 2010) than corn with more floury endosperm.

Vitreousness increases with increasing maturity at harvest (Phillipeau and Michalet-Doreau, 1997), so differences among corn hybrids are greatest when field dried. Because corn silage is harvested earlier than high-moisture corn, the grain will have less vitreous endosperm and more moisture when harvested from the same field as whole-plant silage compared with high-moisture corn.

However, there can be large differences in vitreousness within corn silage harvested between 30% and 40% dry matter and within high-moisture corn harvested between 60% and 75% dry matter (40% and 25% moisture) from the same field.

Adjust dietary starch throughout lactation
When grains are ensiled, the ruminal fermentability of starch can be greatly affected by both grain moisture concentration and storage time. This is because ensiling solubilizes endosperm proteins over time, increasing starch fermentability. The increase in protein solubility and starch fermentability over time is greatest for grains with a higher moisture concentration (Figure 1; Allen et al., 2003). Therefore, the change is greatest for wetter corn silage and least for drier high-moisture corn.

This change is greatest over the first few months of ensiling and must be anticipated and accounted for when formulating rations. Because of this, it is recommended to wait several months after ensiling before feeding corn silage (Allen, 1998). However, the change continues for months at a slower rate, and corn silage and high-moisture corn that are stored for long periods (one to two years or more) can be difficult to feed in high concentrations because they are so readily fermented.

Processing increases the rate of starch digestion, and the effects are greater for grains with more vitreous endosperm, such as sorghum and corn (Huntington, 1997). Access of enzymes to starch granules is increased by steam flaking, which causes swelling and disruption of the kernel structure, and by reducing particle size by rolling or grinding whole grains or processing silage to crush kernels, which greatly increases surface area.

Dry grains can be finely ground, greatly decreasing the effects of endosperm vitreousness on ruminal fermentability. Processing (rolling) corn silage is not as effective at increasing surface area as fine grinding; processing can reduce, but not eliminate, differences in the digestibility of sources varying in vitreousness.


Concentration, fermentability

Starch concentration is relatively consistent within cereal grain types but varies greatly within forages containing starch, such as corn silage and small grain silages. Therefore, book values for starch concentration may be acceptable for cereal grains, but starch concentration must be measured for forages from grain crops.

For instance, the starch concentration of corn silage varies from less than 20% to more than 50% of dry matter (DM), depending on grain concentration, which, in turn, is dependent upon genetics, environment and maturity at harvest. The starch concentration of corn silage is inversely related to the concentration of neutral detergent fiber (NDF); the fibrous stover fraction of the plant is enriched if kernels don't fill.

The non-fiber carbohydrate (NFC) concentration of diets should not be relied upon as a measure of starch concentration. The NFC fraction is calculated by subtracting measured components (NDF, crude protein, ether extract and ash) from total DM. It contains other carbohydrates such as sugars and pectin and can be underestimated to the extent that non-protein nitrogen is present.

While starch, sugars and pectin are generally highly digestible, their effects on rumen microbial populations and fuels available to the animal differ greatly. Starch that is ruminally fermented increases propionate production in the rumen (Sutton et al., 2003) and starch that escapes ruminal fermentation provides glucose that is absorbed or metabolized to lactate in the small intestine (Reynolds et al., 2003).

Sugars are nearly completely fermented in the rumen and generally increase butyrate production (Oba, 2011). Most strains of pectin-degrading rumen bacteria produce acetic and formic acids and relatively little propionic acid (Dehority, 1969).

Propionic and lactic acids are glucose precursors, while formic, acetic and butyric acids are not. In addition, propionate can decrease feed intake under some conditions (Allen, 2000), and starch, sugars and pectin have different effects on microbial populations in the rumen that can affect fiber digestion and ruminal biohydrogenation of fatty acids.

Therefore, NFC is not a useful proxy for starch when formulating rations for lactating cows.

Relative differences in the rate of starch digestion can be determined by in vitro starch digestion (IVSD) with ruminal microbes. This can be done by incubating samples over time in rumen fluid with buffered media and evaluating the rate of starch disappearance or by evaluating starch disappearance over a period of time (e.g., seven hours), which is less costly but equally informative.

My laboratory group began using a seven-hour incubation time more than 20 years ago, when our objective was to predict in vivo ruminal digestibility of starch because we thought it was a reasonable mean residence time of starch in the rumen of lactating cows. However, we subsequently realized that was naive because the ruminal digestibility of starch in vivo is highly affected by the enzyme activity of the rumen fluid and particle size of the starch source, and that residence time of starch in the rumen is extremely variable not only across cows but also across sources of starch (Table).

We continue to use IVSD with a seven-hour retention time because we think it provides useful information about relative rates of fermentation among starch sources. However, it is very important to know that seven-hour IVSD is a relative measure of the rate of starch digestion among sources only.

Samples must be ground before analysis, which removes important variation for many comparisons (e.g., processed versus unprocessed corn silage). Comparisons must be done during the same in vitro run (at the same time) because IVSD of the same sources is highly variable across runs.

This is because enzyme activities (amylases and proteases) of rumen fluid are highly variable from cow to cow, time relative to feeding and diet consumed. In my laboratory, the coefficient of variation for seven-hour IVSD across runs can be as high as 25% even after attempting to minimize variation by taking rumen fluid from several cows fed a specific diet at the same time of day relative to feeding. This is much higher than the coefficient of variation of less than 3% for 30-hour in vitro NDF digestibility.

Because starch digestion is inhibited by insoluble proteins in the endosperm, the solubility of protein has been measured as an indicator of relative differences in starch digestibility. Like IVSD, determining protein solubility requires grinding samples, removing variation among sources. Because protein solubility is a chemical rather than biological measure, it is less variable across runs than IVSD. The accuracy of ruminal starch digestibility prediction from protein solubility is limited by the relationship between protein solubility and the rate of starch digestion as well as by limited knowledge of the passage rate of starch from the rumen.

Therefore, like IVSD, measures of protein solubility provide some information related to ruminal starch digestion but cannot be used to measure ruminal starch digestibility accurately.


Prediction by models

Although measuring the digestion rate of feed fractions in vitro and in situ can provide relevant information regarding relative differences among feeds, models require absolute -- not relative -- values to predict ruminal digestibility.

Therefore, despite their promise, ration formulation models that include rumen sub-models, such as CNCPS, do not predict ruminal starch digestibility accurately even if in vitro rates of starch digestion are used as inputs (Allen, 2011).

The accuracy and precision of predicting ruminal starch digestibility was poor for several models, including CPM and AMTS, in a recent evaluation; AMTS and CPM over-predicted ruminal starch digestibility for corn grain by more than 25 points (about 80% compared to 55%), leading the authors to conclude that the model estimates were not useful (Patton et al., 2012).

The primary factors limiting accurate determinations of digestion rate in vitro or in situ are: (1) the inability to mimic the increase in surface area and breakdown of particle size by rumination, (2) the variation in enzyme activity and ratio of enzyme to substrate in the rumen over time and (3) a lack of understanding and data on passage rates of starch.

Rates of starch digestion determined in vitro are much different from actual rates of digestion because feed particles containing starch that are consumed by cows are larger than what is required for in vitro analysis and because enzyme activity in the rumen is extremely variable depending upon diet, time since eating and the cow.

Grinding feeds is necessary to obtain uniform samples for analysis in the laboratory, but grinding increases the surface area accessible to microbes, which increases the rate of digestion compared to intact feeds in vivo. On the other hand, not grinding at all will underestimate the rate of digestion because feeds are crushed and ground by chewing over time, before they pass from the rumen.

This is an unsolvable problem because simulating the effects of chewing over the time of incubation in vitro or in situ is infeasible.

The high variation in IVSD across runs prompted my team to evaluate the effect of rumen fluid, sampled before and after feeding, on seven-hour IVSD, which was 33% greater after feeding compared to before feeding (41.2% versus 30.9%, P < 0.01; Fickett and Allen, 2002). Enzyme activity related to starch fermentation is also increased with higher-starch diets; we reported that the fractional rate of starch digestion determined in vivo with the pool and flux method was greater for diets with a higher starch concentration and lower NDF from forage (Oba and Allen, 2003a) or beet pulp (Voelker and Allen, 2003b).

Therefore, at least for starch, digestion is a second-order process dependent upon both substrate and enzyme activity. This creates a problem for utilizing current data with most existing models in which digestion is modeled as a first-order process dependent on feed characteristics only.

The passage rate of starch was greatly affected by particle size, conservation method and endosperm type for corn (Table; Ying and Allen, 2005; Allen et al., 2008). However, few data exist for the passage rate of starch and how it is affected by diet and level of intake. Because passage rate is as important as digestion rate for determining ruminal starch digestibility, accurate predictions by models that use digestion kinetics to predict starch digestibility are not currently possible. In addition, models that use digestion rates for carbohydrate fractions but passage rates for entire feeds produce even greater inaccuracies in their ruminal starch digestion predictions.


Production response

Adjust dietary starch throughout lactation
The filling effects and fermentability of rations are affected by the concentration and ruminal fermentability of starch and can affect dry matter intake (DMI), nutrient partitioning, microbial protein production and total-tract digestibility.

Increasing the starch concentration of the ration offered to lactating cows from about 23% to 34% (from about 24% or 16% forage NDF, respectively) resulted in variable effects on DMI and fat-corrected milk (FCM) yield, depending on the milk yield of cows. The range in FCM was about 50-130 lb. per day. DMI response to the high-starch, low-forage NDF ration increased linearly with increasing milk yield of cows throughout the range, while FCM response increased only for cows producing more than about 90 lb. of FCM per day (Voelker and Allen, 2003a; Figure 2).

Response for DMI was likely because the higher-starch diet was less filling (16% forage NDF) and rumen fill becomes a greater limitation to feed intake as milk yield increases (Allen, 1996), while the response for FCM likely depended upon effects of the ration on digestibility and energy partitioning among cows.

The physiological state of animals determines the effects of starch fermentability on DMI (Bradford and Allen, 2007) and production (Bradford and Allen, 2004) responses. High-moisture corn had the opposite effects of dry ground corn on milk yield for cows, depending on the initial milk yield, with no change for the group overall; high-moisture corn increased the concentration of milk fat and yield of FCM for cows producing more than 90 lb. per day but decreased both for cows producing less than that amount (Bradford and Allen, 2004).

The effect of treatment on DMI was not related to milk yield but was affected by the physiological state of cows; depression in DMI due to the high-moisture corn versus the dry corn treatment was related to plasma insulin concentration and insulin response to a glucose challenge (Bradford and Allen, 2007). Feed intake of cows with greater insulin concentration -- and lower insulin response to a glucose challenge -- was depressed to a greater extent by high-moisture corn compared with dry ground corn.

As lactation proceeds and milk yield declines, feed intake is increasingly dominated by metabolic signals. Highly fermentable diets often decrease feed intake in mid- to late lactation, likely from stimulation of hepatic oxidation by propionate (Allen et al., 2009). Reducing the ruminal fermentability of starch by substituting dry corn for high-moisture corn in rations often increases energy intake and partitioning to milk for these cows.

Energy partitioning between milk production and body condition varies depending on fuels available and as the physiological state changes throughout lactation. Substituting fiber for starch greatly alters fuels available for intermediary processes and often results in greater partitioning of energy to milk rather than body condition.

Substituting soybean hulls for dry ground corn for up to 40% of diet DM increased milk fat percentage linearly from 3.60% to 3.91% and decreased bodyweight gain linearly from 1.02 kg to -0.14 kg per day, with no effect on milk yield (about 29 kg per day) but a slight decrease in DMI (tendency, linearly) from 23.8 to 22.7 kg/g (Ipharraguerre et al., 2002).

My research showed that beet pulp decreased body condition score without decreasing yields of milk or milk fat when substituted for high-moisture corn for up to 12% of diet DM (Voelker and Allen, 2003a). Furthermore, a 69% forage diet (0% corn grain) containing brown mid-rib corn silage increased energy partitioned to milk, decreasing bodyweight gain while numerically increasing FCM yield compared with a 40% forage diet (29% corn grain) containing control corn silage (Oba and Allen, 2000a).

In contrast, DMI and milk yield were reduced when the control corn silage, which had 20% lower in vitro NDF digestibility (46.5% versus 55.9%) than the brown midrib corn silage, was fed in the higher-forage diets.

As lactation proceeds, insulin concentration and sensitivity of tissues increase, and energy is increasingly partitioned to body condition. An intravenous glucose infusion of up to 30% of the net energy requirement linearly increased plasma insulin, energy balance, bodyweight and back fat thickness without affecting DMI or milk yield of mid-lactation cows (Al-Trad et al., 2009).

An experiment conducted with cows in the last two months of lactation showed that substituting beet pulp for barley grain linearly decreased body condition score and back fat thickness, maintained milk yield and linearly increased milk fat yield and milk energy output (Mahjoubi et al., 2009). The decreased body condition score and increased milk fat yield might have been because of a linear decrease in plasma insulin concentration, which linearly increases plasma non-esterified fatty acid concentration.

High-starch diets might result in greater insulin concentration, partitioning energy to adipose at the expense of milk, but they also often result in lower ruminal pH and, thus, in milk fat depression from altered biohydrogenation of polyunsaturated fatty acids in the rumen, which reduces milk energy output. While increased energy retention as body condition might be because of increased insulin, as observed by Ipharraguerre et al. (2002) and Mahjoubi et al. (2009), it might also be a result of altered gene expression in adipose tissue.

Harvatine et al. (2009) reported that conjugated linoleic acid-induced milk fat depression increased gene expression for enzymes and regulators of fat synthesis in adipose tissue. The energy spared from the reduction in milk fat synthesis was likely partitioned toward adipose tissue fat stores. Reducing ration starch concentration by increasing fiber from forages or non-forage fiber sources can maintain milk yield while decreasing gain in body condition.

Increasing the ruminal degradability of starch generally increases microbial nitrogen flow to the duodenum, but excessive ruminal starch digestion might decrease ruminal fiber digestibility, offsetting its effects (Firkins et al., 2001).

In addition, starch sources with faster rates of fermentation might decrease the efficiency of microbial protein production; microbial growth can be uncoupled from organic matter fermentation under some conditions (Russell and Cook, 1995).

A greater concentration of starch in rations (32% versus 21% of DM) increased the flow of microbial nitrogen from the rumen with no effect on the efficiency of microbial nitrogen production in a study my laboratory conducted using lactating cows (Oba and Allen, 2003b). However, although ruminal starch digestibility was increased by high-moisture corn compared with dry ground corn in that experiment, high-moisture corn decreased the efficiency of microbial nitrogen production compared with dry corn and did not affect the flow of microbial nitrogen from the rumen.

While the flow of microbial nitrogen was positively related to true ruminal organic matter digestibility in that experiment, it was negatively related to the rate of starch digestion across all cow period means. Microbial growth might be limited when the rate of starch digestion is very fast (Oba and Allen, 2003b). Therefore, increasing ruminal starch degradation by increasing the starch concentration of diets might improve the flow of microbial nitrogen to the duodenum to a greater extent than increasing the ruminal fermentability of starch.


Formulating for starch

A great deal is known about what factors affect the ruminal digestibility of starch that can be routinely used for ration formulation, even if rates of digestion and passage of starch cannot be accurately measured.

Starch concentration and ruminal digestibility are so variable across feeds that one can measure starch concentration and use literature values for ruminal digestibility for the initial formulation, which can be adjusted using qualitative knowledge of the factors that affect ruminal starch digestibility discussed previously.

Although one should strive to increase the accuracy of prediction over time, animal responses to starch concentration and fermentability cannot be accurately predicted because of the many interactions that ultimately affect the response, such a stocking density, effective fiber concentration, milk yield, physiological state, etc. However, ration formulation should be an iterative process that includes cows in the loop; evaluating cow responses will provide feedback to optimize diets. Cow responses include DMI, milk/fat/protein yields, milk urea nitrogen, body condition, manure consistency, ketones, etc.

Grains that differ in ruminal starch fermentability but have high whole-tract digestibility (e.g., high-moisture corn and ground dry corn) allow for the evaluation of optimal ruminal starch digestibility without other confounding effects (e.g., effects of changing forage NDF concentration on feed intake), and the dietary starch concentration can be reduced by substituting a non-forage fiber source -- such as beet pulp, soybean hulls or corn gluten feed -- for grains.

Group feeding complicates the interpretation of responses for DMI and milk yield. Mean milk yield for the group masks the effects of diets because large changes in milk yield of individual cows within the group might occur with no change in milk yield for the group overall. This is most evident when all lactating cows (with great differences in physiological state) are offered the same diet. Individual milk meters provide timely feedback regarding the response of individuals within the group and are an important tool for diet formulation and grouping.

The same is true for individual DMI response, but this is not feasible economically for group-housed cows. While that limits the usefulness of DMI determination for the group, it is still a very useful measurement, particularly in combination with milk yield, to provide important clues for the effects of the dietary change.

Evaluation of cow responses requires nutritionists to pay more attention and coordinate with the farm management team. The extent to which nutritionists and the management team interact will vary from farm to farm, but this is an important determinant of the success of the nutrition program.

The following recommendations for ration starch concentration and ruminal fermentability for cows as they progress through lactation should be adjusted as indicated based on cow response:

* Fresh cow ration (from parturition to 10-21 days following parturition). Fresh cows are in a lipolytic state and at an increased risk for metabolic disorders, and feed intake is likely controlled by oxidation of fuels in the liver (Allen et al., 2009). These cows require glucose precursors, and rations should contain higher starch concentrations to the extent possible. However, these cows also have lower rumen digesta mass, which increases their risk for ruminal acidosis and displaced abomasum.

Highly fermentable starch sources increase fermentation acid production, including propionate, which can stimulate oxidation of fuels in the liver, thus suppressing feed intake (Allen et al., 2009). Therefore, highly fermentable starch sources should be limited during this period, which lasts for up to two weeks for most cows but even longer for cows with excessive body condition at parturition.

Highly fermentable starch sources -- such as wheat, barley, low-density steam-flaked corn and aged (more than one year old) high-moisture corn and corn silage -- should be limited to allow for greater starch concentrations (and glucose precursors) with less risk of acidosis or displaced abomasum. Supplementing corn silage-based diets with dry ground corn works well for the fresh cow ration with a total starch concentration of 22-25% (DM basis).

Because feed intake is less limited by ruminal distention during this period, and greater rumen digesta mass is desirable, the forage NDF concentration should exceed 23%, and the use of non-forage fiber sources should be limited to diluting the starch concentration, if necessary. Starch concentrations must be decreased when feeding highly fermentable starch sources.

* Early- to mid-lactation ration. Cows in early to mid-lactation have a high glucose requirement for milk production and partition relatively little energy to body reserves. They respond well to rations with a lower forage NDF concentration (low fill) and highly fermentable starch. The starch concentration of rations should be in the range of 25-30% (DM basis), although the optimal concentration is dependent upon competition for bunk space, forage/effective NDF concentration and starch fermentability.

Higher-starch, lower-fill rations generally increase peak milk yield and decrease loss of body condition in early lactation. However, once cows replenish the body condition lost in early lactation, they should be switched to a maintenance diet with a lower starch concentration and ruminal fermentability.

* Maintenance ration (more than 150 days in milk and a body condition score of three). The maintenance ration is the key component of a ration formulation/grouping system to increase the health and production of cows. The goal of the maintenance ration is to maintain milk yield and body condition throughout the rest of lactation.

Cows should be offered the maintenance ration when they are regaining body condition and reach a score of three. If they continue receiving a high-starch diet, body condition score will continue to increase, and they will be at increased risk for metabolic disease following parturition.

Evidence presented herein suggests that these cows are gaining condition because they are being fed rations with more starch concentrations than needed for their current requirement for milk production, which increases plasma glucose and insulin concentrations. Lowering the ration starch concentration should limit body condition gain while maintaining and possibly improving feed intake and yields of milk and milk fat.

The optimal concentration of starch is dependent upon the milk yield of the herd and physical groups possible but will likely be in the range of 18-22% (DM basis). Starch sources that are highly fermentable (high-moisture corn, bakery waste, aged corn silage, etc.) should be avoided. Dried ground corn is an excellent starch source because it has lower ruminal digestibility (about 60%) but high total tract digestibility (< 90%).

The starch concentration of the maintenance ration should contain an adequate but not excessive forage NDF concentration to maintain DMI, and non-forage fiber sources (beet pulp, corn gluten feed, soybean hulls, etc.) can be used to dilute starch to the target concentration. Monitoring the body condition score at dry-off is essential in order to adjust the starch concentration of the maintenance diet over time.



The concentration and ruminal fermentability of starch are highly variable among rations fed to lactating cows and have great effects on feed intake, energy partitioning, milk production and health. The optimal starch concentration and starch source in rations vary by the physiological state of cows, which changes throughout lactation.

Cows should be fed different rations throughout lactation to maximize the use of existing knowledge regarding starch nutrition.



The complete list of references appears with this article at www.Feedstuffs.com or can be obtained by emailing [email protected]


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Sutton, J.D., M.S. Dhanoa, S.V. Morant, J. France, D.J. Napper and E. Schuller. 2003. Rates of production of acetate, propionate and butyrate in the rumen of lactating dairy cows given normal and low-roughage diets. J. Dairy Sci. 86:3620-3633.

Taylor, C.C., and M.S. Allen. 2005. Corn grain endosperm type and brown midrib-3 corn silage: Site of digestion and ruminal digestion kinetics in lactating cows. J. Dairy Sci. 88:1413-1424.

Voelker, J.A., and M.S. Allen. 2003a. Pelleted beet pulp substituted for high-moisture corn: 1. Effects on feed intake, chewing behavior and milk production of lactating dairy cows. J. Dairy Sci. 86:3542-3552.

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Voelker, J.A., G.M. Burato and M.S. Allen. 2002. Effects of pretrial milk yield on responses of feed intake, digestion and production to dietary forage concentration. J. Dairy Sci. 85:2650-2661.

Ying, Y., and M.S. Allen. 2005. Effects of corn grain endosperm type and conservation method on site of digestion, ruminal digestion kinetics and microbial nitrogen production in lactating cows. J. Dairy Sci. 88S:393.


Effects of dietary treatment on passage rate (kp) of starch from the rumen



kp, %/h


Oba and Allen, 2000b

bm3 corn silage




Control corn silage




29% diet NDF




38% diet NDF



Oba & Allen, 2003a

High-moisture corn




Dry ground corn



Voelker & Allen, 2003b

High-moisture corn




24% beet pulp



Ying & Allen, 2005

High-moisture corn




Dry ground corn




Vitreous endosperm




Floury endosperm



Taylor & Allen, 2005

Vitreous endosperm




Floury endosperm



Allen et al., 2008

Vitreous endosperm




Floury endosperm



Note: Determined by dividing duodenal flux (g/h) by rumen pool size (g) and multiplying by 100.



Volume:85 Issue:15

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