Practical application of feeding forages
Alfalfa and corn silage are the most widely used forages for dairy cattle in the Midwest while grasses and pasture are used more in beef cattle diets. Alfalfa became the forage of choice in dairy cow diets because it was higher in crude protein compared to grass and thus would lower purchased protein costs. Corn silage provided good yields of consistent forage high in energy. If we look at changes in feeding of forage to dairy cows over the last 50 years, we can see why changes occurred. It was anticipated that milk cows would go up in production when turned out on grass in the spring of the year. Very likely, that reflected the consumption of both higher protein and also higher NDF digestibility (NDFD) grass forage. In contrast, the forage the cows had been consuming may have been from a two or three cut system. In the Midwest, it was likely an alfalfa/grass mix with brome or timothy. These grasses tend to mature faster than alfalfa and so would be low in CP and NDFD, and high in NDF. But we were working with crude fiber as an analytical measurement. As we progressed into the 1960's and 70's we discovered that with proper structures we could harvest low moisture hay silage and speed up harvest and feeding through mechanization. This enabled multiple cut systems resulting in higher quality haylage and higher haylage diets. In the mid-70's, we also had very high soybean meal prices and high haylage diets helped offset the cost of purchased protein. In some cases, diets were haylage and large amounts of high moisture corn. Dairy cows increased in milk production but we also started to experience incidences of displaced abomasum. We also had places where either due to economics or winterkill of alfalfa, corn silage started to make a comeback. Researchers Goering and Van Soest developed the detergent system of forage analysis and NDF was determined. We began to understand how and why forages fed like they do. Over the next 30 years, the continued increase in understanding of forages has allowed us to double and even triple milk production from what is was in the 1950's and 60's while reducing the footprint of making milk. We now understand more fully the components of fiber, how it digests, fractions of crude protein, the need for effective fiber, and differences in species of forage.
It is now 2015. By fall, the forage supply for most farms is set in both quality and amount. Feed costs are moderate but margins are still tight. How do we make the best use of this year's forage supply and what should we think about for the future?
Corn silage has become the dominant base forage used on many dairy farms. Corn silage offers many advantages to a feeding system. It is high yielding, very consistent, very palatable and is high in energy. Its main challenge is that it is low in protein. Corn silage brings two components to the diet fed: forage and grain. Within each component there can be variations in digestibility, which needs to be determined. Analysis needs to be done in order to determine both a set time NDFD, such as NDFD30 and uNDF240, or total tract NDFD (TTNDFD). Further, a prediction of the rate and extent of ruminal starch digestion is valuable.
In recent years, several new forage tests have been developed to more precisely predict the nutritive value of forage and enable nutritionists and cattle producers to better utilize forages in feeding animals. Feeding forage is not only necessary for healthy animals but also is a source of lower cost nutrients in a ration. Higher quality forage allows producers to include greater amounts in diets while reducing inclusion of grain or other purchased feeds; thus reducing feed cost. Higher quality forage also leads to greater dry matter intakes and higher milk production or rate of gain. Too often, producers have focused on the crude protein content of alfalfa and grass forage and did not realize the value of NDF digestibility and possible energy contribution. Subsequently, the challenge becomes getting enough forage NDF if the alfalfa is very high quality while limiting soluble protein. Conversely, limiting necessary added starch for energy if NDF is too high and NDFD is low. Maximizing the amount of forage fed and optimizing production is a multi-component balancing act. Forage digestion is a process of rate and extent of NDF digestibility. High productivity is possible only by having forage that is both high in rate and extent of NDF digestibility. This combination leads to greater dry matter intake and a greater input of nutrients into the milk production process.
Ash content and uNDF240 have become more important in predicting a more accurate forage energy value. Determining the organic portion of measured NDF (NDFom), eliminates overestimating total NDF of the forage. Overestimating NDF can result in insufficient forage NDF and excess starch in the diet fed compared to the computer program output.
Advances in forage testing have resulted in advances in ruminant nutrition. We now have a better understanding of what makes better forage. It is more than crude protein content. NDFD is probably the single biggest component of forage quality. Become familiar with the terms associated with forage analysis now being used. Look for NDF, NDFD, uNDFD240, ash content as well as crude protein.
Forage testing pays!