Forage quality affects profitability
May 12, 2007
Competition for corn to use for ethanol, feed and food has caused a doubling in the price of corn as compared to a year ago. As the soybean market competes for acres, it has caused a related rise in the price for soybeans. Consequently, the price for all feed ingredients has risen considerably.
Quality forage has always been the foundation on which healthy, productive diets for dairy cattle have been based. Lundquist (1995; Fig. 1) illustrated this very nicely in his diagram of the food pyramid for cows. I changed the pyramid (Fig. 2) to show greater emphasis on the forage portion, which may reflect the diets in the future.
Forage can supply energy (corn silage), protein (alfalfa), starch (corn silage), NDF (corn silage and alfalfa), and minerals (corn silage and alfalfa). Maximizing the forage portion can reduce off-farm feed inputs.
In order to maximize the amount of forage that can be fed, great emphasis must be put on harvesting high quality forages. What is quality forage? For this article, let us focus on alfalfa and grass forages. First, it is important to have forage that is palatable and readily consumed, and results in positive animal performance such as milk production or growth. Although legumes such as alfalfa and clover are generally higher in crude protein, other quality factors have greater impact. While protein and minerals are costly, they can be added to the diet.
The stage of maturity is very important for harvesting high quality forage. Why? Digestible energy is most likely to be limiting in low quality forage and this is most affected by advancing maturity. The rate and extent of NDF digestibility determines intake potential and energy potential. NDF increases and digestibility decreases with advancing maturity (Fig. 3). Research tells us that there is a strong negative correlation to NDF concentration and intake potential. As NDF increases, animals fill up faster and this limits intake. As forage matures, physiological changes occur that decrease the digestibility of NDF. At the bud stage of growth in alfalfa, leaf growth is essentially maximized but the stems continue to elongate and increase lignification. This increases the portion of stem material, which is lower in NDF digestibility as compared to leaves.
Figure 3. NDF Digestibility of Alfalfa Stems
Source: Jung and Lamb, 2002. Unpub USDA-ARS.
Lignin is an indigestible compound in NDF and, as it increases, it also interferes with microbial access to cellulose further limiting digestibility. This limits rate and extent of digestion, intake of forage and, thus, energy consumed.
Relative Feed Value (RFV) and Relative Forage Quality (RFQ) are similar methods of ranking forage based on predicted energy content. RFQ has replaced RFV in recent years because it more accurately predicts energy values by using digestibility of NDF in the equation. Because of this, RFQ also better estimates nutritive value of grasses when compared to alfalfa than does RFV.
Most people who grow alfalfa are familiar with a PEAQ stick. PEAQ stands for predictive equations for alfalfa quality. PEAQ sticks provide a quick, simple and effective tool to help you determine when you should cut first crop alfalfa at the RFV or RFQ you desire. PEAQ sticks are not well correlated to RFQ for second or later cuttings. Wisconsin research, which resulted in the development of the PEAQ stick, shows that RFV drops approximately 5 points for each additional inch of height at a given stage of development but drops approximately 20 points when changing from early bud to early bloom at a constant height.
It may be an advantage in fields with winter damage to delay first cutting to allow root reserves to replenish. This can impact desired forage quality. North Dakota research shows total dry matter yield to be similar across a 3- or 4-cut system. However, RFV values averaged 150 for a 3-cut system and 172 for a 4-cut system.
Newer PEAQ sticks predict RFQ but there have been some inconsistencies in actual RFQ values compared to stick predictions. This may be due to additional factors such as the growing season, which can affect fiber content.
I would recommend each producer have their own PEAQ stick. Every field and farm is different due to soil type, south facing slopes, age of stands and other factors. PEAQ sticks can be ordered from the Midwest Forage Association office at (651) 484-3888 or at their website: www.midwestforage.org.