Submitted to: Professional Animal Scientist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/21/2009
Publication Date: 3/17/2010
Citation: Soder, K.J., Hoffman, K. 2010. Effect of molasses, corn meal or a combination of molasses plus corn meal on ruminal fermentation of orchardgrass pasture in continuous culture fermenters. Professional Animal Scientist. 26(2):167-174. 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. Therefore, a research study was conducted to evaluate the effect of pasture supplementation with molasses or corn meal on ruminal fermentation in continuous culture. Experimental treatments were: 1) orchardgrass pasture-only; 2) molasses plus orchardgrass pasture; 3) corn meal plus orchardgrass pasture; or 4) molasses plus corn meal plus orchardgrass pasture. While protein digestibility was increased with molasses supplementation, there was no effect on dry matter or fiber digestibility, ruminal pH, volatile fatty acids, or microbial protein production. Under low levels of inclusion, molasses or corn meal supplementation, alone or in combination, did not greatly impact ruminal fermentation of a pasture-based diet. Pasture-based dairies that supplement with molasses may need to consider supplementation rates greater than 5% of total dry matter intake to observe any potential benefits. Additionally, potential interactions with other feeding factors, such as forage quality, must be evaluated. Effects at the animal level (milk production and composition, body condition score, and conception rates) must also be evaluated. Finally, the cost of the relatively expensive organic grains and sugar sources must be considered in supplementation decisions.
Technical Abstract: Although molasses is being used by organic dairy farmers as a lower-cost energy alternative to corn, little research currently exists evaluating the effects of molasses as the sole supplement on ruminal fermentation of grazing dairy cows. This study evaluated the effects of pasture supplementation with molasses on ruminal nutrient digestibility and bacterial nitrogen synthesis in continuous culture fermenters. Experimental treatments were: 1) orchardgrass (Dactylis glomerata L.) pasture-only (control; PAST; 70 g DM/d); 2) molasses plus orchardgrass pasture (MOL; 3.5 g DM/d molasses plus 66.5 g DM/d pasture); 3) corn meal plus orchardgrass pasture (CM; 4.9 g DM/d corn meal plus 65.1 g DM/d pasture); and 4) molasses plus corn meal plus orchardgrass pasture [MOL+CM; 3.5 g DM/d molasses plus 4.9 g DM/d corn meal plus 61.6 g DM/d pasture]. Treatment did not affect (P is greater than 0.05) apparent DM, OM, and NDF digestibilities; true DM and OM digestibilities; molar proportions of VFA; or acetate to propionate ratio. Mean ruminal pH tended (P is equal to 0.071) to be greater for MOL. Maximum ruminal pH was greatest (P is less than 0.05) for MOL. Ruminal NH3-N was lowest (P is less than 0.05) for MOL+CM. The CP digestibility was greatest (P is less than 0.05) for MOL and lowest for MOL+CM. Total flow of NH3-N tended (P is equal to 0.078) to be lower for MOL+CM. Flow of dietary N was lowest (P is less than 0.05) for MOL. Bacterial N flow (g/d) and efficiency of bacterial N synthesis were not affected (P is greater than 0.05). Under low levels of inclusion, molasses or corn meal supplementation, alone or in combination, did not greatly impact ruminal fermentation of a pasture-based diet.