The Value of Spring Pasture in a Nutrient Program

  By Jaclyn Krymowski

 Springtime has traditionally been a much-anticipated season on the dairy. In the old days, farmers looked forward to renewed milk flow back when the term “springers” was a bit more literal. With the farm’s evolution to luxuries of year-round calving’s and a multitude of feed sources, this time of year   doesn’t have quite the same nutritional and managemental gravity it did in days gone by. What has not changed is the season bringing in opportunities for forage growth and harvesting, meaning operations of all types and sizes will be being managing and harvesting their hay and pasture. For some, the spring growth is still utilized as a serious nutritional component in the diets of heifers, lactating and dry cows. Regardless of how heavily you rely on your grass, what is offered is only as good as the effort put in.

What’s the value?
When properly managed and regulated, pastures of very many plant species can be very high in nutritional content and quality. In fact, it can even be superior to high quality conventionally stored feedstuffs. Not to mention, it is much more economical than machine harvesting.

Similar to hay and haylage, age of harvest is pivotal to nutritional value. In an ideal setting, pasture grasses are consumed in a vegetative state approximately 6-8 inches tall and typically less mature than when they’d be cut and stored. If you take a look at the popular forage growth pattern chart (available from the Iowa State University Extension service) you’ll notice the cool season grasses and forage legumes spike in the spring, things like your clovers, orchardgrass and fescue. These nutrient-dense feedstuffs contribute to higher crude protein, especially late spring through early summer. This value drops as the weather gets warm, then tends to go back up again in October.

Crude protein is but one type of this major pasture nutrient. Unfortunately, even the best pastures are also high in rumen degradable protein (RDP). According to Penn State it is often 70-80% of a pasture’s total protein that ends up degraded in the rumen. Using concentrates to offer ruminally available carbohydrates can help animals use the RDPs more effectively. Also, worth noting, the most limiting nutrient for lactating cows in pasture-based system is energy. Concentrations are also excellent for supplemental energy and carbohydrates.

Measuring quality for need
Like any other feed ingredient, pasture can be nutritionally analyzed. However, this is significantly more challenging than taking a simple core sample from a bale or silage bunk. And even with analyzation, the sensitivity and behaviors of individual animals determine what plants they eat and how much. This means different nutritional values among herdmates, unlike what you’d get with TMR. It is still possible to get as uniform a sample as you can and try to at least have an idea of what your cows are being offered.

Sampling should take place when the grasses are first adequate for harvest. Walk the entire pasture and obtain at least 25-30 samples, but more may be necessary for larger pastures. The best way to collect samples is to grasp about where a cow would wrap her tongue around. Try to get uniform samples and avoid outliers that are excessively weedy, near water sources and manure. You can tear off the roots and any clumps of dirt, try to keep the “grazing” part of the plant the cow would use. To prevent any fermentation that would affect the composition of your sample, remove as much air from the bag as possible and place the sample in the freezer. It is best to keep the sample frozen as you ship it to the lab to eliminate this risk all together.

Because there is a lot of variability between the grazing seasons, nutritionists recommend annual testing of soils and grasses. For milking groups that rely heavily on pasture, it may be even necessary to re-formulation rations even throughout the grazing season based on the forage changes.

Many operations, even if not reliant as a key dietary component, will utilize pasture for dry cows. Because of the lower nutritional needs of these animals, it is easy for their forage quality to be overlooked and less emphasized. But even when it’s “just” dry cow pasture, they deserve an extra eye on what they’re eating. For example, northeastern region pastures can be excessively high in potassium which is known to cause issues in late pregnancy and during the transition. Different studies have concluded simply feeding anionic salts were not enough to counteract this for close-up cows.  In such a case, addressing the forages at the source is the only solution instead of additional fixations.

Growing heifers are less sensitive, but still need to be monitored carefully. If fed properly, calves will have enough rumen development to harvest and utilize pasture at around 6 months of age. From 6 to 12 months, it is recommended that heifers be supplemented with a concentrate ration to supply adequate energy needed for growth. Once they’re over a year old, healthy heifers can do quite well on adequate grass and legumes without any excess supplementation.

Spring grazing can be a wonderful complement to your herd’s nutritional program. It should be treated with the same gravity and understanding as if it were any other forage ingredient. And remember, managing grass is key. A beautiful “spring flush” can be thwarted very quickly by overgrazing and hoof traffic. Treat your grasses well and they will do likewise to your animals.