Effect of molasses supplementation and nutritive value on ruminal fermentation of a pasture-based diet

Authors: Soder, Kathy; BRITO, A - University Of New Hampshire; HOFFMAN, K - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2010
Publication Date: 2/1/2011
Citation: Soder, K.J., Brito, A.F., Hoffman, K. 2011. Effect of molasses supplementation and nutritive value on ruminal fermentation of a pasture-based diet. Professional Animal Scientist. 27:35-42.

Interpretive Summary: Escalating organic grain prices and significant changes in milk contracts have forced organic dairy farmers to seek alternative energy sources for organic dairy cows. Sugar cane molasses, a rich source of sugars, appears to be a viable, less costly source of supplemental energy and minerals. However, milk production responses have been mixed on organic dairy farms that have used molasses as the sole energy supplement. Previous research suggests there may be a significant forage quality by molasses level interaction, however, this has not been evaluated with dairy cows grazing northeastern pastures. Therefore, a study was conducted to evaluate the effect of forage quality and level of molasses supplementation on nutrient digestibility, ruminal fermentation and microbial protein synthesis of a pasture-based diet in continuous culture. Experimental treatments were: 1) high-quality pasture with molasses supplemented at 5% of total dry matter fed; 2) high-quality pasture with molasses supplemented at 10% of total dry matter fed; 3) low-quality pasture with molasses supplemented at 5%; 4) low-quality pasture with molasses supplemented at 10%. While nutrient digestibility, ruminal pH, and volatile fatty acids were increased with high-quality forage, there was no molasses by forage quality interaction. These results suggest that there are many variables that must be considered by organic dairy farmers in supplementing dairy cows with molasses, including forage quality, cost, ease of feeding, and availability. Molasses may need to be evaluated on a case by case basis to determine whether it may be a feasible supplement alternative, with careful attention paid to cow body condition and production to evaluate the success of molasses supplementation.

Technical Abstract: Molasses is used by some grazing dairy producers to replace higher-cost corn. However, anecdotal results are mixed, and little research exists evaluating the effects of molasses fed to grazing dairy cows as the sole supplement. This study evaluated the effects of level of molasses supplementation and forage quality on ruminal fermentation in continuous culture fermenters. Using a 4 x 4 Latin square design with treatments arranged in a 2 x 2 factorial, treatments were: 1) high-quality pasture (63 g DM/d) plus blackstrap molasses at 10% of total DM fed (7 g DM/d; HI10); 2) high-quality pasture (66.5 g DM/d) plus molasses at 5% of total DM fed (3.5 g DM/d; HI5); 3) low-quality pasture (63 g DM/d) plus molasses at 10% of total DM fed (7 g DM/d; LO10); and 4) low-quality pasture (66.5 g DM/d) plus molasses at 5% of total DM fed (3.5 g DM/d; LO5). Apparent OM and ADF digestibilities and true DM and OM digestibilities were greater (P less than 0.05) for the HI10 and HI5 treatments. Mean ruminal pH was greater (P less than 0.05) for the HI10 and HI5 treatments. Concentrations of total and individual VFA were greater (P less than 0.05) for the HI10 and HI5 treatments. The CP digestibility and bacterial N efficiency were not affected (P greater than 0.10). No significant interaction between forage quality and level of molasses supplementation relative to ruminal fermentation were detected. Molasses may need to be evaluated on a case by case basis to determine feasibility as an energy substitute for grazing dairy cows.