There has been a recent upsurge in sugar usage in dairy cattle diets to boost fiber digestion and rumen fermentation. Molasses holds high sugar concentrations, which are highly soluble in water and include disaccharides and monosaccharides. Molasses is a syrupy substance consequential from refining sugarcane or sugar beets into sugar. The introduction of sugars in dairy feeds is essential in helping the microbes within the rumen capture and use nitrogen efficiently. The added sugar alters the microbial population within the rumen, thereby increasing the number of lactate-consuming bacteria. This phenomenon leads to heightened production of butyrate, dry matter intake, and high milk fat yield. Prevalence of superior butyrate production resulting from consuming a high-sugar diet is anticipated to improve the proliferation of gut tissues and the overall production of the cow. Nonetheless, there is limited evidence to indicate how adding sugar in the form of molasses in the dairy cow diet improves the cow’s rumen fermentation and fiber digestion.
Rumen fermentation involves processes that enable the host to convert ingested food to energy. Sugar is commonly regarded as a carbohydrate fraction that easily ferments when in the rumen. Though dairy diets are not necessarily formulated to a certain sugar concentration, most feedstuffs used for dairy diets comprise different levels of sugar content. Fiber and starch are the prime sources of carbohydrates in diary feeds; however, sugars make crucial sources of energy with significant effects in rumen fermentation. Sugars change the volatile fatty acid profile, which is essential in rumen fermentation (Sun et al., 2020). Since the nature of fermentation end-products affects animal nutrient use, it becomes essential to understand how sugars change the volatile acid profile. A literature review by Oba (2011 on various vitro studies has shown that feeding molasses can raise butyrate production within the rumen. Rumen fermentation occurs during hydrolysis when disaccharides change to monosaccharides which undergo further hydrolysis (Liu et al., 2021). However, the rate at which disaccharides undergo hydrolysis is contingent on the type of sugars.
The hydrolysis rate of Sucrose tends to be faster than that of lactose within diary animals not adapted to the subjunction of lactose or Sucrose in their diets. In a literature evaluation, Oba (2011) finds that the hydrolysis of lactose is higher in animals adapted to a high lactose diet than those adapted to high sucrose diet. The assessment reveals that microbial adaptation is necessary for the hydrolysis of various disaccharides. The appraisal could also mean microbial adaptation is necessary for the hydrolysis of certain disaccharides. The rate of fermentation also varies in different types of monosaccharides. An analysis conducted on fructose, glucose, arabinose, galactose, and xylose indicates that fructose and glucose undergo almost complete fermentation when subjected to a 2-hour vitro incubation. Only 50% of galactose was fermented during the analysis, and arabinose and xylose (Oba, 2011). Therefore, Sucrose is likely to ferment entirely when in the rumen due to heightened hydrolysis and successive fermentation of monosaccharides. Assessments by Oba (2011) reveal that a limited amount (less than 5 percent) of lactose might escape rumen fermentation and spread to the duodenum, thereby contributing to enzymatic digestion.
Different studies have been conducted to determine the effects of the inclusion of molasses on a daily diet. However, the findings do not frequently come to a similar conclusion as they are influenced by varying levels of molasses and different diets. Reviews from Mordenti et al. (2021) show that a diet with moderate starch should be combined with moderately soluble fiber content when feeding additional sugars. Findings by Deusch et al. (2017) reveal that balancing various carbohydrate fractions is a critical step as each can influence the composition of the rumen microbiome. The review also indicates that usage of moderate doses of molasses intensifies ruminal fermentation, protein synthesis, microbial activity, and minimal ammonia levels in ruminal liquid.
Adding sugar to a dairy diet has substantially enhanced rumen fermentation by increasing the rumen pH. Sugars tend to undergo faster fermentation compared to other carbohydrates. This phenomenon is expected to lower the pH of the rumen. Nonetheless, a study by Ravelo et al. (2021) specifies that the pH of a rumen is likely to increase following a partial substitution of dietary starch sources with sugar. Though earlier studies have indicated feeding diet with Sucrose instead of ground milo reduced the rumen pH, this finding might be attributed to the high low dietary forage allocation (De Ondarza et al., 2020). There exists limited literature to provide concrete evidence that increasing dietary sugar levels reduces rumen pH. It is not known that feeding sugar tends to increase the rumen pH because sugars ferment faster in the rumen.
Different theories define the occurrence of this situation among diets rich in sugar. One account indicates that sugar offers reduced carbon when matched up to starch for fermentation acid production for every unit of mass. Another description for the lack of lower pH at the rumen after sugar diet revolves around microbial glycogen synthesis (Hall, 2019). Microbes can convert Sucrose to glycogen which acts as short-term energy storage. This activity provisionally lowers fermentation acid production within the rumen, thereby leading to increased rumen pH.
Sugars or molasses-based liquid supplements are some of the readily available energy sources for dairy cattle. The fungi critical in fiber break down are triggered by the 6-carbon sugars (Malhotra & Chapadgaonkar, 2018). Proper control of the level of starch within the ration is likely to influence the rumen pH, thereby enhancing fiber digestibility. In a situation where the sugars are added to dairy rations at 6 to 8% of the total ration dry matter, molasses can boost dry matter intake and neutral detergent fiber (PDF) digestibility (Mordenti et al., 2021). Different physical factors of the ratio can affect adding molasses to the animal diet. In rations where the molasses used is at a level of 12% or higher than the grey matter, the effect will be a reduced dry matter and fiber digestibility (Campos et al., 2020). Dairy diets formulated with sugar at 8% less diet matter catalyze fiber digestion. Some of the factors that influence the effect of molasses on fiber digestion include the forage form, ration particle size, and the fiber level within the ration.
Reviews of different literature indicate that molasses has a substantial effect in improving rumen fermentation and fiber digestion. Sugars have shown rapid fermentation in the rumen; replacing dietary starch sources with sugar does not necessarily reduce the rumen pH. Therefore, sugar offers a reliable substitute for carbohydrate sources within dairy diets. The sugar raises the energy density of diets coupled with reduced rumen acidosis. The 6-carbon sugars provide sufficient energy necessary to trigger the fungi critical in fiber breakdown among dairy animals. Research findings indicate that feeding dairy cattle sugars not exceeding 8 percent of the diet matter improves fiber digestion. Feeding high-sugar diets is highly linked with heightened butyrate concentration within the rumen, thereby enhancing nutrient absorption.
References
Campos, F. P., Nussio, L. G., Sarmento, P., Daniel, J. L. P., & Lima, C. G. (2020). Effects of addition of different sources and doses of sugars on in vitro digestibilities of dry matter, fibre and cell wall monosaccharides of corn silage in ruminants. Animal, 14(8), 1667–1675.
De Ondarza, M. B., Emanuele, S. M., & Sniffen, C. J. (2020). Dietary sugars for optimizing rumen function and Dairy Cow Performance. Handle Proxy.
Deusch, S., Camarinha-Silva, A., Conrad, J., Beifuss, U., Rodehutscord, M., & Seifert, J. (2017). A structural and functional elucidation of the rumen microbiome influenced by various diets and microenvironments. Frontiers in Microbiology, 8.
Hall, M. B. (2019). Sugar in diets for lactating dairy cows. DAIReXNET.
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Malhotra, G., & Chapadgaonkar, S. S. (2018). Production and applications of xylanases – An Overview.BioTechnologia, 99(1), 59–72.
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Oba, M. (2011). Review: Effects of feeding sugars on productivity of lactating dairy cows.Canadian Journal of Animal Science, 91(1), 37–46.
Ravelo, A. D., Calvo Agustinho, B., Arce-Cordero, J., Monterio, H. F., Bennet, S. L., Sarmikasoglou, E., Vinyard, J., Vieira, E. R. Q., Lobo, R. R., Ferraretto, L. F., Vyas, D., & Faciola, A. (2021). Effects of partially replacing dietary corn with molasses, condensed whey permeate, or treated condensed whey permeate on ruminal microbial fermentation. Journal of Dairy Science.
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