By Matt Akins

With the need for high-quality forages to feed lactating cows, it can be difficult to balance diets for dairy heifers — especially pregnant heifers. Diets based on corn silage and alfalfa work well for young heifers up to 12 months of age. However, pregnant dairy heifers up to two months before calving have lower energy needs (58% to 62% total digestible nutrients) for recommended gains of 1.8 to 2.2 pounds per day.

Targeting for 60% TDN and 50% neutral detergent fiber has worked well in feeding studies. Delaying harvest of alfalfa or grasses to increase fiber and reduce energy would work well. Alternatively, higher-fiber forages can be combined with corn silage or alfalfa to dilute diets. Higher-fiber diets reduce intake since heifers have an intake limit of about 1% of body weight as NDF each day. A 1,000-pound heifer will eat about 10 pounds of NDF. If the diet contains 45% NDF, the heifer will eat 22 pounds of dry matter; however, at 50% NDF, the heifer will eat about 20 pounds dry matter.

Work at the Marshfield Agricultural Research Station evaluating the warm-season, perennial grass called eastern gamagrass showed the greatest forage yield (3 to 4 tons dry matter per acre) from a single harvest in mid-September, with quality ideal for partially replacing corn silage to reduce diet energy. Dry matter (DM) content in mid-September is 30% to 40%, so minimal or no wilting is needed. Use of eastern gamagrass at 20% to 30% of the diet has worked well in heifer diets. A unique feature of gamagrass is its high palatability with minimal sorting.

Straw and corn stover also work well in heifer diets. Typical inclusion rates are 10% to 20% of diet DM for the desired energy content. Sampling is recommended, as variation exists in fiber content, digestibility and mineral content. Sorting can be an issue, with corn stover being more sortable than straw, but this can be reduced by prechopping to 2 to 3 inches in length or adding water for a target diet DM of 45% to 50%. Also, it is advisable to feed for minimal refusals of 1% to 2% to minimize sorting.

Other options
Cereal grain forages such as wheat, rye, triticale and barley are also options, with many producers having potential to use these due to increased adoption of cover crops. Harvesting at boot stage is recommended for lactating cows or young heifers, while heading stage is ideal for pregnant heifers. Yields have been 1 to 2 tons of DM per acre at these stages (harvested from late May to early June), with potential to still double crop thereafter.

Sorghums — forage sorghum and sorghum-sudangrass — are another lower-energy, higher-fiber option.  Conventional and photoperiod-sensitive sorghums are ideal to blend with haylage or a protein byproduct (e.g., distillers grain, gluten feed). Harvesting as a single harvest had one-and-a-half to two times greater yield than a two-cut system, but protein and energy were lower. At the Marshfield ARS, yields of conventional sorghum-sudangrass (planted in early June in 15-inch rows at 20 pounds per acre) harvested as a single harvest in late October to early November were 6 to 8 tons of DM per acre. When planted late (past late June), the crop may not reach soft to hard dough stage, and moisture content will be too high for a single fall harvest, so cutting and wilting may be needed. Use of shorter-maturity varieties can help in this situation.

Producers have several forage options for feeding dairy heifers. The choice depends on cropping and rotation systems on each operation. Discussion with your agronomist and nutritionist is recommended to determine best options and management practices.

Akins is an assistant scientist and Extension specialist in Marshfield, Wis. Wayne Coblentz, a research dairy scientist with the USDA Dairy Forage Research Center in Marshfield, contributed to this column. This column is provided by the University of Wisconsin-Extension Dairy Team.