Addition of Sugars to Dairy Rations

Responses to sugars in dry or liquid form vary from study to study. To explain some of this variation and prioritize when sugars are more likely to have a benefit in diets for high producing dairy cattle, microbial function that influences susceptibility to low ruminal pH or a limitation in growth factors needed for efficient ruminal fiber degradation is discussed in this paper. When fed in proper amounts, sugars should not depress ruminal pH, and there is some evidence that they actually help to prevent a drop in pH after consuming large meals of concentrate by maintaining a higher number of lactate-fermenting bacteria. Adding sugars does prioritize the need for rumen degraded protein (RDP). However, lactate-fermenting bacteria probably compete against the bacteria that catabolize amino acids as their main energy source, so feeding sugars potentially preserve higher concentrations of peptides and amino acids for the rest of the microbial consortium to degrade fiber or produce microbial protein more efficiently. Sugars tend to increase butyrate or valerate concentration in the rumen, which, besides consolidating 2 moles of acid into one, provides more fuel for rumen epithelial cells. We don’t know if this helps to increase surface area and absorptive capacity from the rumen wall in lactating dairy cows, but there is growing evidence that cows that are more likely to resist subacute rumen acidosis tend to have increasing concentrations of these fermentation endproducts. Moreover, sugars do not promote the formation of trans fatty acids that are implicated in milk fat depression, and there is some evidence that they might decrease the accumulation of these fatty acids by slowing lipolysis or modifying rates of biohydrogenation. Combined with the potential to reduce sorting behavior against coarse particles, especially in corn silage-based diets, our data with liquid feeds tend to support the same or enhanced milk fat yield, particularly if dry matter intake (DMI) is increased.