The concentration of forage fiber can be important when formulating diets with distillers grains for Back »

Sanjeewa Ranathunga, a doctoral candidate with the Dairy Science Department at South Dakota State University (SDSU), has been investigating the interaction of forage level with dried distillers grains (DDGS) for lactating dairy cows.  Distillers grains is an excellent source of protein and energy. Though the dairy industry is a large consumer of DDGS, there are some challenges to overcome when using DDGS.  One concern is the low physically effective fiber in DDGS and the second is the amount of linoleic acid, a polyunsaturated fatty acid.  Linoleic acid is often cited as the reason for milk fat depressions when lactating dairy cows are fed DDGS, however other factors can be involved. Therefore, the objective of this research was to investigate the interaction between the amount of the forage with the amount of DDGS in the diet on ruminal fermentation, nutrient digestion, milk production and milk composition of lactating dairy cows.

Three studies were conducted using the same four dietary treatments of two forage fiber concentrations (neutral detergent fiber; NDF) with two inclusion rates of DDGS.  Treatments were:  1) Low forage (17% forage NDF) and 0% DDGS; 2) Low forage (17% forage NDF) and 18% DDGS; 3) High forage (24% forage NDF) and 0% DDGS; and 4) High forage (24% forage NDF) and 18% DDGS. The low forage diets contained 32.8% corn silage, 8.2% alfalfa hay, and 59% concentrate mix, whereas the high forage diets contained 48% corn silage, 12% alfalfa hay, and 40% concentrate mix. 

In the first study, Sanjeewa demonstrated that lactating dairy cows fed 18% DDGS performed similarly to diets without DDGS (corn based diet). This supported previous SDSU research demonstrating that DDGS can be used to replace corn as an energy source. Also, this study revealed that feeding DDGS may not be the major factor responsible for milk fat depression when DDGS are fed to lactating dairy cows.  Sanjeewa found that the milk fat depression occurred only on the low forage diet, whereas the inclusion of 18% DDGS did not reduce milk fat content. This study demonstrated that lactating dairy cow diets can be fed using approximately 20% (DM basis) of DDGS, as long as, there is adequate forage fiber (>21% NDF from forage) in the ration to prevent a reduction in milk fat content.

The second experiment used rumen-cannulated cows to investigate the forage and DDGS concentrations on ruminal fermentation patterns, blood metabolites, and total nutrient digestibility. This study demonstrated that forage and DDGS concentrations influenced ruminal fermentation and blood parameters, however total tract nutrient digestibilities were similar. The ruminal evacuation data that was collected demonstrated that on a low forage diet the NDF from DDGS may be digested to a lower extent than when lactating dairy cows are fed high forage diets.

The third experiment investigated the in situ degradability of the individual TMR’s and the degradability of DDGS. This study confirmed the second study that the ruminal digestibility of NDF in DDGS and the TMR’s containing DDGS was reduced when cows were fed a low forage diet.   

This set of studies revealed that DDGS is fermented differently when the diet contains different forage concentrations. Low forage diets form a less dense ruminal mat, thereby reducing ruminal pH.  Low ruminal pH reduces ruminal NDF digestibility of DDGS and the reduction in the density of the rumen mat allows smaller DDGS particles to exit the rumen quicker. Conversely, high forage fiber diets have a denser ruminal mat, thereby increasing ruminal pH. High ruminal pH may increase NDF digestibility of DDGS through enhancing cellulolytic bacteria.  In addition, a denser ruminal mat may entrap the smaller DDGS particles, thereby reducing the passage rate of DDGS, which results in an increase in fiber digestibility.  Sanjeewa’s studies suggests that the inclusion of DDGS will provide for a better performance response by lactating dairy cows when they are fed a higher forage diet..

Sanjeewa Ranathunga’s work on forage and DDGS concentrations was awarded the Young Dairy Scholar award by the Midwest Branch of the American Dairy Science Association on March 19, 2012.  Sanjeewa is working under the direction of Dr. Kenneth Kalscheur, Associate Professor of Dairy Science, and expects to complete is Ph.D. in dairy cattle nutrition in 2012.

This article written with contributions from Kenneth Kalscheur, SDSU Dairy Science Assistant Professor, Dairy Cattle Nutrition & Environmental Impacts

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