Although one doesn’t normally think of cereal grains as forage alternatives, they also can be used in the dietary space vacated by forage. Cereal grains contribute to less digesta mass in the rumen than NFFS because their retention time and water holding capacity are lower. The extent to which a cereal grain can replace forage in the diet without reducing feed intake or causing ruminal acidosis depends on its digestion characteristics. Cereal grains with moderate ruminal fermentability and high whole-tract digestibility, such as dry ground corn, are desirable to include in diets in place of forage. They are less filling than forages and have higher energy concentrations. They have an advantage over NFFS because more glucose precursors are provided from starch digestion compared with fiber digestion as previously mentioned. Highly fermentable starch sources such as finely ground high moisture corn, barley, wheat and bakery waste should be avoided to prevent excessive fermentation. Starch sources with low total tract starch digestibility such as unprocessed sorghum or coarsely cracked corn should also be avoided because they reduce the energy density of diet.
Ruminal fermentability of starch varies among cereal grains, and it might be possible to increase meal size and feed intake by reducing ruminal fermentability and propionate production. A recent experiment from our laboratory showed that meal size increased from 4.2 to 5.1 lb, and feed intake increased from 45.8 to 49.5 lb/d as dry ground corn replaced high moisture corn in high starch diets fed to lactating dairy cows. True ruminal starch digestibility decreased from 71% for high moisture corn to 47% for dry ground corn with no effect of treatment on total tract starch digestibility (95%). Although actual milk yield was similar for the two treatments, fat-corrected milk yield was similar for the two treatments, fat-corrected milk yield tended to be 6.6 lb/d higher for dry ground compared with high moisture corn treatment because of higher milk fat concentration. When forage is replaced with cereal grains, those grains with slower ruminal fermentation are likely to improve feed intake and milk production, depending on their digestion characteristics and other dietary characteristics as discussed below.
Consideration for Feeding Low-Forage Diets
The forage concentration of diets can be reduced by forage alternatives in many situations; in some, forage alternatives can replace a large fraction of the forage, allowing very low forage diets to be fed. Ohio researchers suggested that when diets for mid-lactation cows contain whole cottonseeds, they can contain as low as 9-11% forage NDF as long as non-structural carbohydrates (starch and sugars) are no more than 30% of diet DM. Diets without whole cottonseeds should contain no less than 14-16% forage NDF and no more than 30% non-structural carbohydrates. Nebraska researchers reported that a wet corn milling product (40% NDF, 23% crude protein) has the potential to replace all of the concentrate and up to 45% of the forage in the diet for lactating cows. The forage content of diets can be minimized by considering the following recommendations.