Milk grasses for all they’re worth

By Cody McCary, Vita Plus forage specialist
“When it heads, the quality is dead.” You’ve probably heard this adage that refers to the abrupt tradeoff between forage quality and yield as grass silages reach more advanced stages of plant maturity.

The stage of plant growth and timing of harvest are essential to achieving the yield and quality goals for a given grass crop. The progression from one stage of maturity to the next often happens rapidly. For example, the boot stage in ryegrass may only last a few short days. When you throw in some unforeseen circumstances – such as weather delays or hotter-than-normal temperatures just prior to and during harvest – you may find yourself easily missing predetermined quality goals. To combat this narrow harvest window, consistent monitoring of in-field conditions and plant stage of maturity is necessary.

Harvesting grass for quality
When harvested at early stages of plant maturity, quality can be maximized with a penalty of reduced yield. Grasses harvested at boot stage commonly have a reduced lignin concentration and increased NDF digestibility compared to grasses harvested at later stages of plant growth. Additionally, an increase in crude protein concentration can also be expected when harvested at earlier stages of plant maturity compared to more mature counterparts. These nutritional qualities are conducive to the needs of high-producing dairy cows and the inclusion of grass in dairy diets has merit to be explored.

Harvesting grass for yield
It is common to hear stories of farms that started with the desire to harvest for quality, harvest ended up behind schedule, the grass reached a later stage of maturity, and the farm now has a lot of low-quality grass inventoried for the next year. In this situation, all is not lost.

The grass crop can be harvested at a later stage of plant maturity and targeted toward dry cows and/or heifers. These later stages of plant maturity capitalize on an increase in yield at harvest and produce a quality of feed more suited for groups of animals with lower energy requirements. Greater NDF and lignin concentration, decreased crude protein concentration, and decreased NDF digestibility should be expected in comparison to less mature counterparts. Additionally, the time that the grass feed is retained in the rumen increases, contributing to greater physical rumen fill and helping to moderate intake.

During harvest, plant dry matter (DM) and stage of maturity should be monitored at all times. With increasing plant maturity, some grasses exhibit a hollow stem structure that increases the silage’s resistance to packing and the elimination of oxygen. It has been shown that increased silage mass packing densities have less DM loss and that the removal of oxygen is necessary for an efficient fermentation. This may necessitate a shorter theoretical length of chop (TLOC) for mature grass stands. Current recommendations for TLOC for grass silage are 0.25 to 0.325 inches.

Grass in diets
Compared to alfalfa, grasses typically contain greater concentrations of NDF and less lignin. Lignin acts as a framework, attaching to more digestible portions of the fiber and limiting NDF digestibility. Therefore, grasses achieve a greater extent of NDF digestion then alfalfa. Less non-fiber carbohydrates (NFC) is observed in grass than in alfalfa. This allows grass to be an option in diets where NFC concentration needs to be moderated and where NDF concentration of the diet may be low. Lastly, grasses have the potential to provide near or equal to the crude protein concentration of alfalfa when harvested at early stages of maturity.

Grasses can provide flexibility in a forage program and help meet production goals. Contact your Vita Plus consultant to discuss how you can more efficiently use your homegrown forages to meet milk production goals.