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How can Sugar Based Liquid Feeds Optimize the Dairy Cows Rations?



Andrea Formigoni (1), Alberto Palmonari (1), Ludovica Mammi, (1)
Phil Holder (2) & Luiza Fernandez (2)


(1)             DIMEVET_Alma Mater Studiorum_University of Bologna

(2)             EDF&Man Liquid feed



When facing farmer’s demands, nutritionist have to formulate diets which:

a-      Stimulate higher milk production as supported by animal genetics in different stage of lactation;

b-    Improve milk composition (protein, fat) and cheese making properties;

c-     Reduce risks of metabolic disease, such as ruminal acidosis;

d-    Maintain efficient innate immune system reducing inflammatory insults in rumen and intestine.


Formulation of rations “right” in theory is not sufficient to guarantee farm-scale responses. The way rations are prepared and managed, as well as feeding techniques, are also very important to achieve optimal and constant results. Up to date, we are aware of the impact that environmental conditions could have on farms (temperatures, humidity, daylight), and also about group management in relation to stage of lactation.

Compared to the past, modern knowledge allows us to better comprehend animal requirements and feedstuff composition, as well as rationing models and software.

The challenge of dairy cow`s nutritionist is to formulate rations adequate in terms of rumen and intestinal digestible nutrients to meet maintenance and production requirements maintaining at the same time a good and healthy digestive function. 

Goal of the present paper is to summarize the role played by the different carbohydrates (CHO) and sugars in particular, within their requirement in milking dairy cow rations.


NDF, aNDFom, uNDF, pdNDF and peNDF

The first step of the ration’s optimisation is the definition of neutral detergent fiber (NDF) requirements.

The original NDF determination changed a lot over the time; the use of sodium sulfite, a-amylase and more recently the ash correction reduced significantly the entity of this fraction inside of forages and concentrates and we have now a more refined estimation of the cell wall content. The last acronym used to identify the structural CHO is now called aNDFom (neutral detergent fiber organic matter, obtained with the use of amylase and corrected for the ash content).

The aNDFom is composed by potentially digestible CHO in the rumen and intestine (pdNDF), and another portion which is considered completely indigestible (iNDF). In the past the iNDF was estimated with a fixed ratio with ADL amount (ADL*2,4), while now it can be analytically determined in vitro at 240h or in vivo at 288h. These long fermentations give a “residue” called uNDF. Many commercial laboratories are now equipped with NIRs curves that can give rapid and economic evaluation of all different fiber fractions in feedstuffs.


Thus, the question for the nutritionist is how much uNDF and pdNDF need to be fed.

Researches run by Bologna University, Miner Institute and Cornell University, suggest that the adequate amount of uNDF which has to be fed is between 0,28 - 0,48% of cow body weight or around of 10-11% of the dry matter (Cotanch et al, 2014; Fustini et al., 2017). These amounts seem to be adequate to maintain chewing and rumination time as well as rumen pH.

The minimum requirement of NDF for lactating dairy cows was proposed by Mertens (1997) at 28-30% of dry matter. Considering that aNDFom give us lower values than NDF, we can speculate that a minimum requirement for aNDFom should be reduced to 25-26% according to Mertens suggestions. It means that a new specific requirement for pdNDF could proposed: approximately a minimum content of 15-16 % on dry matter basis of pdNDF should be included in the ration.

The evaluation of the digestion rate of pdNDF fraction is also important in order to have a better estimation of the available fiber for cellulolytic bacteria to maintain the equilibrium in rumen microbiome; this aspect is essential to meet the energy and the amino acidic requirements of the animals and to maintain a healthy digestive system.


In order to achieve these results, we propose that the minimum requirement of pdNDF fermented in the rumen should be at least equal to the amount of starch degraded in the rumen. 

It is important that daily ration ensure an adequate amount of “long” fiber (mainly from forage) which are responsible of maintaining right chewing time, saliva production and physiological motility of rumen. This parameter known as physically effective fiber (peNDF) first introduced by Mertens many years ago (1997) has been recently widely revised (White et al., 2017). The main factor to consider for peNDF calculation is the size of the particles; however, even particle’s weight, amount of uNDF, and rate of digestion of pdNDF, have a great impact on peNDF efficacy in terms of rumination time and eating behavior. Also, the “fragility” of the forage (different between grasses and legumes) can be considered but this aspect is difficult to measure yet.

From a practical perspective among forages, straw is the best “chewing-promoter”, even when fed at small particle size (< 1-2 cm; Fustini et al., 2011); this effect can be justified by the slow rate of pdNDF degradability, its high buoyancy characteristics and the low fragility under teeth chewing. Based on this experimental data the straw peNDF values can be “forced” to 110-115% of the aNDFom. For these reasons, in many cases, the inclusion of a small quantity of straw could be sufficient to efficiently cover the uNDF and peNDF requirements. 


Moreover, the daily individual chewing time could be measured in several farms, thanks to specific sensors applied to the animal’s neck. For high yielding cows, rumination time should be over 450-480 minutes a day; in these conditions, rations can be more precisely adjusted to optimize the digestive function of animals.   


Soluble fiber

Mainly represented by pectins and some fraction of hemicellulose; soluble fiber (SF) generally is not directly analyzed, but estimated using the following equation: 

SF = 100 – (aNDFom + Crude Protein + Ether Extract + Ash + Starch + Sugars + Organic acids) 

SF is considered a very rapid “fuel” for cellulolytic bacteria. Legumes, “white grains”, and by-products, like beet pulp, are rich in these compounds.

Different trials have been done to evaluate possible replacement of forages and starch with soluble fiber sources (Allen et al., 2013). Results are generally interesting, since milk produced is not affected, while milk fat increases, thanks to an improved butyrate production (both ruminal and intestinal). A significant result obtained by Allen et al. (2013) is related to a slower fattening process of cows in mid lactation when dietary corn was replaced by beet pulp. In this stage of lactation, endocrinal and metabolic assets vary, and peripheral tissues are more insulin–sensitive. Insulin production is stimulated by propionate produced in the rumen from starch, and by the glucose absorbed in the intestine. In conclusion, with a more appropriate use of SF it is possible to reduce the risk of “fat cow syndrome”.

On the other hand, it is also important to remember that if the soluble fiber escapes the rumen, it could reduce the absorption of other nutrients in the intestine, being responsible of several disorders, like diarrhea, and caecal abnormal fermentations. These effects are well known in monogastric animals, in particular when cereals like barley, oat or wheat are used.



CHO commonly used to increase dietary energy support.

Starch structure may vary due to different plant sources, technological treatments, and storage management. Ruminal and intestinal digestibility widely change consequently. On a lab side, starch evaluation is well standardized, while its digestibility is not. Up to date, starch digestibility is estimated with 7h in vitro fermentations, but the proper prediction of both digestion and passage rates is far from being achieved, and thus still under debate.

Several studies have been done to define best inclusion levels of starch in diet, depending on milk yield and stage of lactation. Keeping in mind all the different issues already mentioned, it is common to consider starch as a two-fractions compound: the first is the rumen fermentable, while the second is digested in the intestine.

Considering the factors described above, range of inclusion varies, and could be considered between 18-20% and 28-30% DM, in relation to the amount of starch that has to be fermented in the rumen and digested in the small intestine.

A possible approach in terms of ration balancing, is to equalize the amount of both pdNDF and starch digested in the rumen.


Major concern about fermentable-starch inclusion is related to the risk of sub-acute rumen acidosis. This disorder is not always easy to diagnose, and in any given farm, not all animals are affected, even if fed with the same diet (Khiaosa-ard et al., 2018).

Recent researches conducted at the University of Bologna, underline that the response is strictly individual, and varies a lot among animals.

In general, practical and scientific expertise suggests that starch-rich rations deeply modify the microbial ecosystem in the rumen, inducing severe shifts of microbial populations, which affect animal metabolism and production performance. It was observed in recent studies that such changes would reflect in severe alteration of rumen epithelium, leading to an increased local and general inflammatory status, which in turn promotes SARA associated pathologies, such as laminitis or liver disease (Zebeli & Ametaj, 2013; Garcia et al., 2017).



“Simplified” CHO fraction, represented by monosaccharide (single molecules), disaccharides (from 2 to 20 units of monosaccharides) or oligosaccharides (long chains).

Monosaccharides can have from 3 to 6 carbon atoms. The 6-carbon atoms types, also called hexoses sugars, such as glucose, fructose or galactose) are usually rapidly fermented in the rumen, while pentoses (xylose, mannose, arabinose, contained in forages) are slower as reported in Table 1 (Miron, 2002).

 Table 1. Ruminal degradability of the hexoses monosaccharides - glucose and fructose – and of pentose xylose.



Digestibility %








Among disaccharides, sucrose and maltose (hexoses) are easily fermented in rumen fluid, while xylose (pentoses) is not; also lactose required a certain “lag-time”.

It has been assumed that 100% of the Mono and disaccharide sugars escaping fermentation will be digested in the small intestine.  This may be true for the 6 carbon sugars from cane and beet molasses, but there is evidence that lactose is not as well digested. 

Research has shown that 5 carbon sugars which will predominantly come from the hemicellulose from the breakdown of fiber are not as well digested in the small intestine and only to a certain extent in the hindgut.  


Nutritional role of sugars is to supply the microbiome with rapidly available energy (figure 1), but also to modulate rumen functions, stimulating specific niches, and to preserve the status of the epithelium.


Figure 1. Effect of different sources of carbohydrates in the synthesis of microbial protein in vitro (Strobel, H. J., & Russell, J. B., 1986).

 Several studies have reported improvements in ruminal butyrate concentrations when dietary sugar levels were increased as a partial replacement for cereal grain starch (DeFrain et al., 2004, 2006; Chibisa et al., 2015; Oba et al., 2015) and this mechanism can explain the major sugars advantages observed in the field:

 -HIGHER RUMINAL EFFICIENCY: butyrate is a growth factor for ruminal epithelium (Malhi et al., 2013). Dairy diets containing higher percentages of sugars can increase its production and therefore promote a more efficient energy absorption through the ruminal papillae.

 -PH STABILITY: Butyrate generates only one H+ while others VFA (volatile fatty acids) like propionic and acetic generate 2 H+. That means that by increasing butyrate proportion production and promoting a faster absorption of all VFA in the rumen, sugars are able to better control rumen PH in comparison with starch. 

 -MILK FAT INCREASE: sugars stimulate the growth of Butyrivibrio fibrisolvens bacteria that produce butyrate. This lead to an inhibition of ruminal trans-10 biohydrogenation pathway, explaining the higher milk fat synthesis generally observed when substituting parts of starch with sugars in the ration of ruminants (Sun et al, 2015)


The sugars therefore act as modulators of the ruminal microbiota and improve the trophic state of the ruminal mucosa when adequately integrated in the rations.

Another interesting aspect related to the presence of sugars in the rations is related to their influence on the digestibility of the fibre (Broderick et al, 2008) which could be, at least in part, mediated by a greater presence of rumen fungi. The increase in fibre digestibility can also explain the general positive impact on feed intake when sugar is added to the rations.


The effects on nitrogen metabolism are also interesting. In 1993 Chamberlain et al. showed that the soluble sugars are superior to starch as an energy source for nitrogen fixation in the rumen microbial. Those evidences were also illustrated in the work of Pina, 2010


Table 3. Effect of different sources of carbohydrates microbial protein synthesis (Pina, 2010). 








Rumen ammonia mg/l







Microbial protein synthesis, g/day








A greater nitrogen fixing in the rumen leads to a reduced nitrogen loss through faeces and urine providing beneficial results to the environment as demonstrated by Hristov et al., (2005) but not by Broderick et al., (2008).


Glycerol is a liquid by-product obtained from biodiesel production, and is available as animal feedstuff since several years. Glycerol is a sugar alcohol, with three hydroxyl groups (-OH) that are responsible for its solubility in water.

Three pathways of glycerol in the rumen have been estimated, and include passage (13%), fermentation (44%) and absorption (43%). Early reports on glycerol suggested rapid fermentation to propionate by ruminal bacteria. In vitro fermentation studies suggested that Selenomonas spp. were the major fermenters of glycerol, with the main products being propionate, lactate, succinate and acetate. However, other end products from glycerol fermentation have been reported. The most consistent response from both in vitro and in vivo experiments appears to be a slight increase in proportion of propionate and a greater increase in butyrate (Krebbiel C.R., 2008). Glycerol has been proposed as glucose precursor for dairy cows or for ketosis treatment, with modestly favorable results not comparable with those obtained by the use of Propylene Glycol (Overton, 2007).

Feeding 1 kg/head/day of glycerol instead of 1 kg of dry corn meal positively influenced intake and milk fat content and fat corrected milk (Formigoni et al., data not published). Results obtained by Donkin et al., (2007) did not confirm the improvement of feed intake and milk production but a reduction in milk urea N content has been observed indirectly indicating a more rapid bacteria growth.


Organic acids

Organic acids (citric, aspartate, fumarate and malate) cannot be strictly considered among the carbohydrate fractions but their content in young fresh forages and hays rapidly dehydrated are important representing up to 4-5% of the dry matter (Callaway et al, 1997; Formigoni et al., 2003), (Table 4). Organic acids are able to modify ruminal and intestinal fermentation stimulating and/or depressing the activity of specific bacteria.  Malic acid in particular is an important metabolite for ruminal microbial population since it improves the uptake of lactic acid by Selenomonas ruminantium (Evans and Martin, 1997) and Megasphaera elsdenii (Rossi and Piva, 1999). Several studies have shown the benefit of adding malic acid to the diet of steers and dairy cows on ruminal fermentation (Martin, 1998; Sahoo and Jena, 2014).


Table 4. Influence of time and drying method on organic acids content of alfalfa (g/kg) 

Time after cutting, hours










































(*) Dehydrated with air at low temperature (<100°C); (Formigoni et al., 2003).


Molasses composition

Recently, different trials were made at the University of Bologna to better clarify molasses composition and variability, since any reference in literature is not accurate enough, and up to 15% of the dry matter content was still unknown.

The study analyzed 16 cane and 16 beet molasses samples sourced worldwide. Gravimetric method was used to determine DM, Kjeldhal for CP, sugars and starch via enzymatic method, minerals by ICP, organic acids and other components by HPLC.  This approach was able to characterize 97.4% and 98.3% DM of cane and beet molasses, respectively.

Cane showed a lower dry matter content compared to beet molasses (76.8±1.02 vs 78.3±1.61% as fed – a.f.), as well as CP content (4.8±1.7 vs 10.5±1.1% a.f.), with a minimum value of 1% a.f. in cane to a maximum of 12% a.f. in beet molasses.

The amount of sucrose was higher in beet compared to cane molasses (48.4±1.5 vs 37.5±4.8% a.f.), but with high variability even within cane molasses (51.00 max to 33.31 min, % a.f.) and beet.

Glucose and fructose were detected in cane molasses (4.06±2.07 and 6.20±2.17% a.f., respectively), showing high variability but almost no monosaccharides were detected in beet molasses.

Organic acid composition differed among molasses. Lactic acid was more concentrated in cane compared to beet (4.69±2.16 vs 3.48±1.37% a.f.), varying from 9.77% maximum to 1.23% minimum within cane molasses. Aconitic acid was found only in cane molasses, while glycolic acid in beet. The total sum of acids ranged from 2% to 14% a.f.

Sulfates, phosphates, and chlorides had a higher concentration in cane molasses, which showed a lower DCAD compared to beet (4.47±4.97 vs 53.94±33.36 meq/100g a.f.). Within the cane group, it varied from +117.63 to -58.59 meq/100g a.f., while in beet from +129.20 to +3.24 meq/100g a.f.

In conclusion, data obtained in this study demonstrates the significant differences in molasses composition, highlighting that a more accurate description and characterization is possible and strictly required especially if its use in animal feed is to be fully optimized.


Impact of sugars and liquid feed on fiber digestibility

Many years ago, it was reported that cellulose digestion is increased by molasses inclusion, but not by starch (Table 5; Arias et al., 1951); moreover, the use of pure sucrose did not produce comparable results obtained with molasses, confirming that this product is not simply a “sugar source”. 

 Table 5. Fiber digestion (24h in vitro) with different carbohydrates 



In our lab, a similar approach was used to evaluate in vitro fiber digestibility at 8, 24 and 48 hours, by adding to fermentation flasks different substrates (Table 6); when molasses, liquid feeds or liquid products were added (6% on DM basis) to a common forage (corn silage), fiber digestibility was higher compared to the forage itself. In particular, molasses resulted in higher digestibility than white sucrose addition and milk whey.

Using the same procedure, 3 different liquid feeds were tested; results indicated that “Milker” was able to significantly improve fiber digestibility.

The liquid feed “Milker” was composed by a blend of different sugars sources and soluble nutrients (molasses, maltose, organic acids, etc.) that gave the greatest fiber digestibility value at 48 hours.

Results obtained by the addition of liquid products blends (“liquid feeds”) specifically formulated, suggest that it could be possible to better manipulate rumen fermentations than using one simple sugar source.


Table 6.  Influence of different energetic substrates on aNDFom digestibility evaluated in vitro


aNDFom  in vitro digestibility





Cane Molasse




Beet Molasse




Starch pure




Sugar white (sucrose)








Whey Milk




Milker (ED&FMan)





Impact of molasses on in vitro gas production and microbial population

To better investigate the specific effects of sugars and molasses on the whole rumen environment, in vitro sugar digestibility, gas production, VFA production and impact on microbial populations was tested with the use of cane and beet molasses. It was observed that hexoses are well digested (up to 95%) within the first 2 hours, while pentoses are slower, xylose in particular (80% on average after 24h; Figure 1).

Sucrose in molasses was completely degraded within 1-2 hours confirming its high rate of degradation. The Kd values considered for sugars from beet and cane molasses in the database of the last version of the Cornell Net Carbohydrates and Protein System (CNCPS vs 6.55) were changed from 60 to 20%/hour; based on our preliminary data, the previous values considered in CNCPS were probably more appropriate to describe the degradation of sugars contained in molasses.

In terms of gas production, the addition of molasses anticipated the exponential phase, which occurred within 2h earlier than “blank” samples (4h). The addition of molasses would induce a shift of VFAs produced at certain time points (1h-24h), decreasing acetate and promoting butyrate (Figure 2).


Figure 1. Single sugar in vitro digestibility at different time points.




Figure 2. In vitro volatile fatty acids produced at different time points (% of the total)




The addition of molasses did change also the microbiome. It was observed an increase of S.bovis but also of M.elsdenii, which ferment the lactate produced by Bovis. Moreover, Butyrivibrio spp. were promoted by molasses addition, and this could partially explain the higher fiber digestibility as well as the increased butyrate. Despite the higher energy supplied, methanogenic population were not affected by molasses addition. Ruminococcaceae family varied depending on the molasses used, but no significant differences were observed.


How much sugar in our rations?

Considering the results in literature and of the preliminary data obtained in our lab, the approach to the dairy cow ration formulation should be oriented to separately consider the individual sugar composition of each ingredient. This more precise approach will be possible when the analytical capabilities for sugar determination will be improved.

Recently, De Ondarza et al. (2017) analyzed 24 researches using a mixed model linear regression analysis. They considered different level of sugars added in the rations (control, 1.5–3%, 3–5%, vs. 5–7% on dry matter), days in milk category within treatment, control milk yield category within treatment, and several continuous nutrient variables.

In cows producing >33 kg of milk/d, added dietary sugar had a greater response (2.14 kg of 3.5% FCM/d; P < 0.0001) than in cows producing 0.15). Nutrient variables with a positive effect on 3.5% FCM yield included added starch and protein B2 (insoluble in boiling neutral detergent but soluble in boiling acid detergent solution). Nonlinear statistical analysis predicted the optimal total dietary sugar to be 6.75% of diet DM. Authors concluded that to optimize 3.5% FCM yield response when feeding additional dietary sugars, a low to moderate starch diet should be fed (22 to 27% of diet DM) in combination with a moderate to high soluble fiber content (6.0 to 8.5% of diet DM).

These data assess the high importance to balance the different CHO fractions, since each one of them is able to specifically drive and impact the composition of the rumen microbiome and more generally the animal responses.


Liquid feeds 

Liquid feeds are very interesting for different reasons, even thanks to their ability to help nutritionists or farmers while rationing considering it takes out the high variability of molasses composition. If we think for example in the big concern of using molasses in dry cows because of the high variability of potassium content, a liquid feed with low, neutral or even anionic DCAD could fit perfectly those group of cows. In the contrary, nutritionists could choose higher DCAD liquid feeds to be used during the summer, for example.

Furthermore, specifically formulated liquid feeds can improve ration palatability more than just pure molasses.

Liquid feeds based on cane and beet molasses can improve ration palatability and reduce any sorting activity of the animal (DeVries et al., 2012). Moreover, when dry TMR is prepared without silages, liquid feeds are very efficient in reducing the presence of dust.

Liquid feeds can be used to support and convey different products like glycerin, propylene glycol, whey, distillers, amino acids, NPN sources, organic acids, additives, minerals, etc.

Digestion of the different nutrients in liquid feeds changes depending on their source; in particular, digestion rates (Kd) change because of the origin of such nutrients, while passage rates (Kp) are generally the same for all the components solubilized. Passage rate for liquid feeds is much higher than solid feed. In high producing cows, with high dry matter intake, it is estimated a Kp of 1.5-2.0%/h for forages, 5-8%/h for concentrates, and more than 14-16%/h for nutrients solubilized in rumen liquor. According to this numbers, a reasonable amount of nutrients from liquid feeds would reach the intestine and can be absorbed depending on respective digestion rates.



Liquid feeds are interesting fort their dietetic and technological roles; they can improve palatability of the ration, reduce cow sorting activity and limit dust presence.

The use of liquid feed rich in sugars and other soluble components (organic acids, minerals, urea, additives, etc.) should be a practical and easy way to properly integrate and balance rations in terms of specific nutrients able to:

- increase dry matter intake, milk production and fat content;

- manipulate rumen and intestinal fermentation;

- improve fiber digestion and nutritional efficiency;

- reduce risk of rumen sub-acidosis, mucosa damages and the innate immune system stimuli with possible beneficial effects on animal health.




Authors thank EDF&Man for supporting activity of researches and Dr.Fagioli Luigi for his analytical support and contribution. 



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