Molasses supplementation in grazing dairies

by Tamara Scully

About 10 years ago, a renewed interest in molasses supplementation occurred as certified organic corn became scarce and prices rose. Seeking to add energy to the diet, many farmers began experimenting with molasses. Some farmers were claiming fantastic results by substituting molasses at one-third of the rate they had been feeding corn meal.

“There have been some train wrecks,” Kathy Soder, USDA-Agricultural Research Service’s Pasture Systems Unit, said, as farmers swapped out molasses for corn. Interest eventually died down, but has been renewed as more producers are going 100 percent grass-fed and turning to molasses for energy.

Soder conducted studies five to 10 years ago, attempting to guide dairy producers in the use of molasses supplementation. She recently reviewed those results as grass-fed dairy farms are growing and seeking non-grain energy sources.

Molasses use

When high-quality pasture is degraded in the rumen, it can travel via two pathways. The rumen microbes can digest it into proteins, which are then utilized by the cow, or it can become a waste product – ammonia – and be excreted from the cow as urea. The microbes require energy in order to do their jobs and process protein.

“If there is not enough energy in the rumen, the protein is broken down to ammonia in the rumen,” Soder explained. “What we’re trying to do… is to provide more energy into the rumen, to provide more microbial protein, to reduce this nitrogen that is being excreted… and to increase milk production, which contains protein.”

In the cow, nitrogen is excreted productively in the milk, or becomes a waste product excreted via urine and feces. The lack of energy in the rumen results in higher milk urea nitrogen (MUN) values.

Molasses contains sugars, versus the starch in corn. Both provide energy, but sugars are degraded differently in the rumen, and there are some differences in rumen fermentation. Too much sugar is toxic to rumen microbes. Combined with the high protein levels of pasture, plus low starch levels, problems can readily arise. A drop of body conditioning score, acidosis, laminitis, decreased breeding efficiency and decreased milk production can occur.

Study results

In vitro studies, using a simulated rumen, resulted in no difference in nutrient digestibility between four pasture-based diets: supplemented with five percent molasses, supplemented with 7 percent corn meal, pasture alone or pasture supplemented with both the corn meal and molasses.

Researchers looked at “how efficiently the rumen was functioning. We were trying to balance energy. We were trying to get the same energy of lactation there,” Soder said.

There was a small, not statistically significant increase in crude protein digestibility with the molasses supplementation, which might have indicated a slight bit better balance of energy and protein. There were no changes to the bacterial efficiency or in fermentation between any of the diets. The ammonia concentrations were high across all diets, although the diet with molasses and corn meal together was a bit lower.

In conclusion, there were “minimal impacts over the pasture diet” when molasses or corn meal was added in vitro, Soder summarized.

Researchers then looked at the interaction between pasture and molasses in vitro, feeding a high-quality and a low-quality pasture, typical like that seen in the Northeast, both alone and both with 5 percent or 10 percent molasses supplementation.

Aside from changes due to the pasture quality, there were no changes in digestibility seen whether or not molasses was supplemented or due to the level of molasses supplementation.

“There were no significant interactions between forage quality and molasses,” she stated.

Soder then moved to on-farm studies in 2008-09. A Central New York dairy farmer that had been feeding molasses as well as corn meal to a 56-cow crossbred herd, and grazing 80 pasture acres, was monitored. The supplementation levels of corn meal and molasses changed throughout the second season based on the farmer’s assessment of forage quality and animal need.

Study results seemed to indicate that when the diet had more corn, MUN values were lower, body condition was higher and milk protein increased. However, the level of corn fed coincided with changes in pasture quality, so no conclusions could be made.

Research then moved to the University of New Hampshire’s organic dairy herd. Cows were split into two groups. Each group grazed separately, on adjacent pastures, all day and night except for twice a day milking, followed by feeding with alfalfa baleage and an immediate return to pasture.

The baleage was supplemented with either molasses or corn meal, fed at 12 percent of the total dry matter intake. Thirty percent of the overall DMI was fed in the barn, while 70 percent came from pasture. Cows were fed using Calan gates to accurately monitor intake. Molasses was poured over baleage; the corn was fed in a tub adjacent to the baleage. The study was conducted from May through September.

The study found no statistical differences in pasture intake between the two groups, although numerically the molasses-supplemented cows did consume a larger amount of pasture. Soder hypothesizes that the top-dressed molasses led the cows to consume more baleage, as the cows on the corn meal supplementation had more feed refusals than the molasses group did.

The molasses group also made an additional pound or two of milk – not a statistically significant amount, but all milk components were the same. They gained a bit more body weight than the corn meal supplemented group, but again this difference was not statistically relevant.

Conclusions

The MUN value was “much higher in the corn meal cows than in the molasses cows,” Soder said. This may be a sign that the sugars in the molasses are a better match for “recapturing the protein in the pasture” more effectively than does the corn meal at the supplementation levels – 12 percent of total DMI – fed in the study. The previous in vitro studies had not shown any changes in MUN values between corn meal or molasses supplemented diets.

“When you go to the cow, the cow doesn’t lie, so we need to listen to them,” Soder said. “Protein is expensive. If you have it you want to keep it. Converting the ammonia to urea was an energy cost that could have been put into milk production.”

They also looked at fatty acid profiles in milk. The conjugated linoleic acid (CLA) level was higher in the corn meal cows than the molasses-supplemented ones. The differences in numbers were not large, but did amount to a 5 percent increase in milk CLA levels in corn meal-supplemented cows. There was a 15 percent difference in the omega-six:omega-three (n6:n3) ratio, with the milk from the molasses-supplemented cows having a ratio of 1.15:1, close to the 1:1 ideal. The corn meal-supplemented group was a bit higher at 1.35:1. No conclusions as to why these levels would be different when the groups were grazing adjacent, similar pastures could be ascertained.

Overall, the research shows that liquid molasses fed at 3.5 pounds can effectively replace the same amount of corn, Soder said. “It’s certainly not the silver bullet” it has been reported to be, however.

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