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Optimizing feed efficiency and income over feed costs on dairy farms is very important because feed is the highest cost associated with producing milk. Some of the primary dietary areas for achieving high feed efficiency are feeding high-quality forage, providing optimum balance of protein and carbohydrates for rumen health, and high digestibility of the cereal grains. Diets for lactating dairy cows generally contain about 70% carbohydrates, with 20% to 25% of the diet consisting of starch. The cereal grains provide most of this starch, but corn silage often contributes a high proportion of the dietary starch. However, the focus of this article will be on improving the digestibility of the cereal grains for optimizing lactating cow performance.
Whole, unprocessed cereal grains are not fed to lactating cows because of the low digestibility that would occur. The high dry matter intake of dairy cows results in a rather fast rate of passage of digesta through the digestive tract, so inadequately processed grains will have low digestibility. Achieving high digestibility of dietary ingredients is critical for getting the most out of feed ingredients, especially during periods of high feed prices.
The two major ways of processing cereal grains are to reduce particle size by: (1) rolling or grinding the dried grains or (2) using a combination of moisture and heat. Reducing the particle size increases the surface area for microbial activity in the rumen and enzyme action in the small intestine. Using heat and moisture results in the gelationization of the starch, which increases its rate and extent of digestion. In general, about 50% of the starch from processed, dry cereal grains is digested in the rumen, and total tract digestibility of the starch in most processed cereal grains is greater than 90% (Table 1). Reducing the particle size of corn, sorghum, or barley increases the total tract digestibility of starch and thus increases the energy available from these feeds (Table 1). Steam flaking of cereal grains further increases their digestibility. The maturity of the grain, level of moisture, and the fermentation that occurs during ensiling results in higher digestibility of starch for high-moisture corn than with dry processing, yet high-moisture corn should be rolled, preferably before ensiling for optimizing energy availability.
With each of these processes, the rate of digestion of starch in the rumen is expected to increase. This increased rate of fermentation can result in increased volatile fatty acid production, and sometimes with increases in lactic acid production, which can cause reduced rumen pH, leading to subacute rumen acidosis (SARA). To reduce the risk for SARA, adequate forage and its particle size must be provided, and the balance of forage neutral detergent fiber (NDF) with non-fiber carbohydrates must be monitored when balancing diets, especially taking into account the amount and rate of digestion of the starch. There is higher risk for SARA when feeding steam flaked and high-moisture cereal grains when there is marginal effective NDF in the diet in comparison to feeding dry processing cereal grains. For optimal utilization of dry processed corn for high-producing cows, mean particle size should be less than 1 mm in diets with 20% to 25% starch and 18% to 21% forage NDF. Particle size sieves for grains are available for use by most dairy nutritionists.
With any processing of cereal grains, there is additional cost. Yet as mentioned previously, some processing is needed for improving digestibility of the grain. The marginal cost of grain processing was calculated using dry rolling as the minimal processing needed (Table 1). Traditionally, rolling grain was used for various sizes of cracked grain, but the rollers would not provide for finely processed grain. Today, some grain processors use modern rollers that have precise roller spacings for reducing particle size to the optimal range. However, other grain processors and farmers use hammermills for fine grinding of grains. The energy cost of operating a hammermill is greater than for a roller mill; thus, cost of processing was assumed at $12 versus $8/ton, respectively. The cost of steam processing, especially flaking, is much higher than for dry processing and was assumed at $30/ton. The marginal cost of processing beyond dry rolling, taking into account the additional cost of processing and the increased energy availability, ranged from $0.05 to $0.14/Mcal of NEL. With the recently high feed prices, the value of NEL is about $0.18/Mcal (N.R. St.-Pierre, Buckeye Dairy News, September 2013 issue; http://dairy.osu.edu/bdnews/bdnews.html). Thus, the marginal cost of processing is less than the value of energy at this time, making the processing economical. However, the utility and labor costs of processing are less volatile than feed prices and will remain high, so when grain prices decrease and the value of energy decreases, the more extensive processing may not be economical, but any of the processing methods resulting in less than $0.10/Mcal of NEL will likely be economical based on historical feed prices.
Dry processing of cereal grains to reduce particle size is essential for improving their digestibility. Further processing by using moisture and heat or harvesting high-moisture corn should be based on value of energy, other ingredients in the diets for promoting rumen health, and equipment and land resources for the use of high-moisture grains. Diets should be formulated taking into account the extent and rate of digestibility of starch sources and providing for adequate effective NDF using high-quality forage.
|Grain||Starch Digestibility (%)1||NEL2 (Mcal/lb)||Marginal Processing Cost3 ($/Mcal)|
|Dry, cracked or rolled||85.0||0.87||Base|
|Dry, finely ground||91.4||--||--|
|Dry, rolled or ground||83.5||0.82||Base|
|Dry or steam rolled||95.8||0.85||--|
1 Data taken from: Firkins, J.L., M.L. Eastridge, N.R. St-Pierre, and S.M. Noftsger. 2001. Effects of grain variability and processing on starch utilization by lactating dairy cattle. J. Anim. Sci. 79:E218-E238.
2 Data taken from: National Research Council. 2001. Nutrient Requirements of Dairy Cattle, 7th rev. ed. Natl. Acad. Sci., Washington, DC.
3 Calculations based on NRC (2001) energy concentrations and assumed processing costs of $8, $12, and $30/ton for rolling, grinding, and steam flaking, respectively.
Maurice L. Eastridge
Professor and Extension Dairy Specialist
The Ohio State University