Effect of Molasses Supplementation on Ruminal Fermentation
Dr. Kathy Soder, animal scientist, USDA-ARS Pasture Systems & Watershed Management Research Unit, University Park, PA
Organic farmers are seeking lower cost supplements since input costs keep rising while milk prices have tended to decline. Molasses may be a lower-cost alternative. It is currently being used by some organic farmers, but it has gotten mixed reviews. It works for some, but not for others. No data exists evaluating molasses as only supplement to grazing dairy cows.
Two continuous culture fermentor studies were done to determine the effect a molasses supplement had on ruminal fermentation. Study 1 looked at molasses supplementation versus corn meal (Soder et al., 2010. PAS 26:167-174). This study looked at the effect of molasses, corn meal, or a combination of the two as supplements to a pasture diet. Study 2 looked at molasses supplementation with differing forage qualities (Soder et al., 2011. PAS 27:35-42).
This experiment uses a continuous culture fermentor system to mimic the rumen of a cow. In the first study that compared molasses with corn meal, the treatments were:
- Orchardgrass pasture only as the control (CON)
- Molasses (5%) + pasture (MOL)
- Corn meal (7%) + pasture (CM)
- MOL + CM + pasture
Ruminal pH, volatile fatty acid (VFA), bacterial nitrogen efficiency, nutrient digestibility, and nitrogen utilization were measured. DM digestibility and neutral detergent fiber digestibility were not significantly different among treatments. However, crude protein digestibility was lowest for pasture and highest molasses and pasture corn meal with pasture and molasses and corn meal with pasture were intermediate in crude protein digestibility.
Ammonia concentration in the fermentor was lowest for the molasses, corn meal, and pasture treatment, but still above the 5 mg/dl minimum to stimulate microbial growth in the rumen. It was highest with the pasture only treatment. However, the molasses with pasture and corn meal with pasture treatments were only slightly lower than the pasture only treatment in ammonia concentration. High ammonia concentrations are a symptom of a diet high in protein and low in carbohydrates, especially in starch. Yet, at the levels of ammonia produced there was no impact on the efficiency of bacterial N synthesis or VFA production.
As it applies to pasture diets, variability in on-farm response to molasses supplementation is due to forage quality variability, molasses source/nutrient content variability, and the variability among farms of the other supplements used. Greater supplementation rates may be warranted, but have been shown to depress nutrient digestibility (Broderick and Radloff, 2004). Cost must be evaluated to make sure the cost of supplementation does not exceed the price received for the extra milk produced, if any.
The implications of the findings in study 1 is that the molasses supplementation responded similarly to the corn meal supplementation in improving in vitro N utilization. Both only provided minimal improvements over a pasture only diet. These supplementation treatments need to be evaluated at the cow level for milk production/composition, body condition, and reproductive efficiency.
In study 2 where molasses supplementation level versus forage quality was looked at, these elements needed to be addressed:
- Forage quality (FQ) may influence response to molasses (Heldt et al., 1999; Titgemeyer et al., 2004).
- There may be an interaction between FQ and level of molasses supplementation.
- This interaction has not been investigated with temperate pastures.
Thus the experiment was set up to evaluate the interaction between
molasses and forage quality.
The treatments were:
- 5% Molasses + Good Quality Pasture (G5)
- 10% Molasses + Good Quality Pasture (G10)
- 5% Molasses + Lower Quality Pasture (L5)
- 10% Molasses + Lower Quality Pasture (L10)
Typical range of forage quality for NE dairy pastures
|Nutritive Value Indicators||Good quality pasture||Lower quality pasture|
|Crude Protein (CP), % DM||26.8||20.4|
|Rumen Degradable Protein (RDP), % CP||65.0||61.0|
|Neutral Detergent Fiber (NDF), % DM||35.9||45.3|
|Starch, % DM||3.8||2.4|
|Water Soluble Carbohydrates (WSC), % DM||11.3||10.8|
|Net Energy of Lactation (NEL), Mcal/lb||0.74||0.65|
Dry matter digestibility was a function of forage quality; the good quality pasture had a higher DM digestibility than the lower quality pasture. Ammonia concentration in the fermentor tended to be lower with lower quality pasture. This is due to the lower quality forage having less protein and thus less N to deal with. Bacterial efficiency was unaffected by molasses supplementation or pasture quality. Production of volatile fatty acids was influenced most greatly by forage quality, being highest with good quality pasture. In actuality, the lower quality pasture was still reasonably good forage.
The implications of this study were:
- No significant interactions between forage quality and molasses supplementation.
- Forage quality not as extreme as in original studies on winter range in Inter-mountain West
Disparity in animal production on farms may be due to a number of factors:
- Timing of supplementation
- Molasses source
- Level of molasses
- Adaptation of cows
The overall conclusions from the two studies were:
- Molasses did not significantly impact ruminal fermentation, either alone or in combination.
- No interaction with forage quality differences found in NE temperate pastures.
- Farms using molasses successfully must consider other management factors that may be cause for ‘success’.
- Cost must be evaluated. Is it increasing the bottom line or not?
- Ease of handling (fly control in summer, cold weather - as slow as [liquid] molasses in January)