Dairy producers continuously ask questions challenging the paradigm of how much forage can be fed to meet the nutrient requirements of high-producing lactating dairy cows. Early-lactation high-producing dairy cows require the production and feeding of forages having both high dry matter and neutral detergent fiber (NDF) digestibility for increasing nutrient supply to meet their nutrient requirements.
In recent times, the economics of milk production have placed more emphasis on forage nutrient digestibility to reduce feed costs. My earlier career work focused on the use of high-forage rations for feeding lactating dairy cows to improve income over feed costs while potentially improving feed efficiency. Forages can be the most economical sources of nutrients for the dairy operation, but there is a wide range of forage digestibility values within alfalfa and corn silage databases.
However, dairy producers have consistently improved their ability to grow, harvest and store highly digestible forages. My work at the Energy Metabolism Unit at the USDA Agricultural Research Service (ARS) has demonstrated that nutrient digestibility is the greatest factor limiting nutrient availability.
USDA Dairy Forage Center researchers and others have reported that one important factor influencing forage digestibility is harvest maturity. Forages harvested at an earlier stage of maturity having greater nonstructural carbohydrate concentrations resulted in increased milk production, milk components and dry matter intakes across several studies. These forages have lower NDF concentrations but also greater dry matter and fiber digestibilities.
In contrast to the harvest timing, another mitigating forage digestibility factor based on limited field observations and in vitro laboratory assays evaluating specific soil and crop additive (SCA) crop production programs have demonstrated an impact on producing forages that have greater nutrient digestibility. These digestibility improvements were achieved via soil base saturation amendments, biostimulants and foliar nutrient applications. The SCA agronomy programs used could improve plant health and growth characteristics. Thus, SCA utilization for crop production (focusing on pH, soil organic matter and base saturation levels) in conjunction with agronomic management (including fertilizer and foliar applications) programs for forage production, theoretically, could improve forage nutrient digestibility.
To our knowledge, at the time of this experiment, no scientific reports existed in the scientific literature evaluating forage production via soil and agronomy crop production programs and their subsequent impact on milk production of early-lactation dairy cows. Thus, a research project was conducted to rigorously test this hypothesis by growing both alfalfa and corn to be harvested for haylage and corn silage production, harvested and fed to early-lactation dairy cows.
The control (CON) was based on South Dakota State University soil and agronomy crop production program (minimal fertilization for only yield, with no focus on quality) compared with an SCA (pH and base saturation) and agronomy management (fertilizer and foliar application) program for forage production.
In the spring, an existing 38-acre alfalfa field was split into two parcels of 23 acres for CON and 15 acres for SCA agronomy program. No spring fertilization due to soil tests was required due to pH of 7.8 and adequate P (145 parts per million) for CON. For the SCA field, gypsum, potash and sulfur (S) were applied before greenup. After greenup, a foliar application of surfactant/penetrant, biostimulants and a micronutrient mix of iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) with additional surfactants and stabilizers was made. First-cutting alfalfa was harvested on May 28 and treated with a silage inoculant when ensiled in silage bags.
A 33-acre field was fully tilled and split into two parcels of 23 and 13 acres for producing corn silage and no manure was spring-applied. The CON parcel consisted of no supplemental fertilizer due to soil tests with a preemergence herbicide applied with a two-herbicide blend applied at canopy. For SCA treatment preplant, gypsum, potash, surfactant/penetrant and biostimulant were broadcast prior to planting. Corn hybrid MC527 was planted at 32,000 kernels per acre with an ammonia, urea, orthophosphoric acid and potassium (K), biostimulant, micronutrient trace mineral mix, liquid K and S being side-dressed. During the growing season, a foliar application of a post-exposure glyphosate micronutrient mix, biostimulant and reproductive micronutrient mix were applied. Corn was harvested as corn silage using a self-propelled forage harvester with kernel processor and treated with a silage inoculant when ensiled in silage bags.
For the feeding experiment, 30 early-lactation (58 days in milk; 85.8 pounds of milk per day) cows were blocked and randomly assigned to one of two treatments based on CON or SCA-produced forages. Lactational performance is given in Table 1, but milk production was increased approximately 13% when cows were fed SCA forages compared with cows fed CON forages, while dry matter intakes were similar. Feed efficiency was improved 17% by feeding SCA-produced forages.
The total-tract apparent NDF (48.5% and 54.7%) and acid detergent fiber digestibility (ADFD) increased, while starch digestibility (97.9% and 98.4%) tended to increase for cows fed SCA compared with cows fed CON. Feeding highly digestible forages during early lactation improved milk production, milk composition and fiber digestibility in a high-forage ration.
Laboratory assays, even though extensive, are still not able to measure all potential parameters that may be important to lactating dairy cows for nutrient digestion and absorption. The improvements in the apparent total-tract NDF, ADF and starch digestibilities would suggest that these dairy cows were digesting, extracting and absorbing more energy and nutrients, which was not predicted by the initial forage nutrient assays. It is not known what forage nutrient parameters the laboratory assays should/could be measuring. However, the dairy cows were apparently digesting and extracting more nutrients to supply the additional nutrients required for an increase of 9.5 pounds of milk per day.
The speculation is that the SCA forage program altered the ether-to-ester linkages of the lignin-fiber relationship in the growing plant, which allowed for more fiber digestion. Altering the ratio of ether-to-ester linkages between the fiber and lignin structure of the plant has the potential to improve nutrient digestibility.
