From July 29th – 30^th the USDA Forage Research Center held the “Getting More From Forages” conference in Madison, Wisconsin explaining their current research efforts to account for ration variability on dairy farms and to improve forage crops and their management to meet the demands of the diverse range of dairy farms. Day 1 focused on animal related management and Day 2 focused on crop related management.

Targeted feeding strategies: Accounting for variability

Adjusting for forage variability via on-farm analysis: Dave Mertens

Dave Mertens of the USDA Forage Research Center expanded upon his topic that he discussed at the 15^th International Silage Conference by explaining in detail how the dry matter (DM) of dairy ration components can change on a farm, affect ration fiber levels and the implications on cow health and milk production.

In high producing dairy cows there is a very narrow range in the ration between neutral detergent fiber levels (% NDF) too low that result in rumen acidosis (Figure 1 red) and too high that result in lower feed intake and lower milk yield (Figure 1 purple). Figure 1 below from Dr. Mertens’ presentation shows how the rations must be balanced more precisely as the fat corrected milk yield per day (FCM/d) goes up.

Basically in order to produce a lot of milk a cow has to eat a lot of feed. The total amount of feed she will eat as a percent of body weight per day (% BW/d), is limited by the % NDF in the ration. For a cow producing 20 kg (44 lb) of FCM/d there is a large range of ration NDF as indicated by the bottom green dashed line across the yellow. Conversely a cow producing 50 kg (110 lb) FCM/d has a very narrow range of ration NDF as indicated by the top purple dashed line in the yellow. Small decreases in the ration’s DM (increases in moisture content) will move the cows into the red zone below their minimal fiber requirements, and may result in rumen acidosis. Small increases in DM % (decreases in moisture content) will increase the amount of NDF in the diet and reduce intake according to Dr. Mertens.

Figure 1: Rations for Dairy Cow Milk Production Levels Limited by DM Intake and Ration NDF

Authors notes:

Mertens’ Figure 1 shows the minimal % NDF as 25%, many nutritionists recommend at least 28% NDF, but the concept is accurate.

Most dairy cow rations are based on alfalfa or corn silage forage, if a farmer is feeding grass silage in the diet, the minimal % NDF can be higher because the higher digestibility of the NDF in grass silages.

Farmers who are trying to maximize milk production through high energy/minimal fiber diets must account for the changes in DM in their silages much more accurately than farmers who feed diets higher in fiber and lower in energy.  Furthermore these farmers are also likely to rebalance their rations more frequently based on other components. In order to do this these farmers need a system that has: frequent sampling, a rapid return of results, an accurate analytical method, simple set and use, and a low cost according to Dr. Mertens. Currently the best option available that would also measure other nutritional qualities besides DM % on farm is a diode array with near infrared sensors. These machines aren’t cheap, $15,000-$35,000, but compared to the costs of decreased animal health and lost milk production they are justifiable for large herds. Dave Mertens demonstrated how these machines could help correct for DM variation of corn and alfalfa silage on farm in order to maintain a minimal amount of NDF in the diet. Figures 2 & 3 below show the changes in the DM % in corn silage and alfalfa silage due to rain and snow events. The amount of NDF in each silage doesn’t change, but the % NDF in each silage will change with variation in the DM %.

Figure 2: Corn Silage DM% Changes Due to Precipitation in a Bunker Silo

The number of farms that can afford the diode array to test their feed on farm is pretty small, but most farmers can still manage DM changes in their silage. If a farm has their feed tested on a monthly basis then a DM% is often already tested. However if the silage gets wet between tests or if a farmer doesn’t have their feed tested, there is a simple method to ballpark the DM %.

This method involves taking a number of samples of the silages, mixing them together, taking a small subsample of the silage, weighing the subsample, and drying it in a microwave with a glass of water inside. Get enough silage samples to fill a two gallon bucket by taking a number samples from non rotted faces of bunkers/bags or putting the bunker under a tower silo unloader for a couple seconds 10+ times.  Also it’s very important to mix the samples well and pull a small amount of silage as a subsample, 100-200 grams or ¼ to ½ lb, on a plate in the microwave. Samples need to be weighed before and after going in the microwave and the weight of the paper plate or bag that the silage is in also needs to be weighed before it goes in the microwave the first time and after it’s taken out the last time. Having a scale that measures small amounts of weight (grams or ounces) is needed. Not putting the glass of water in the microwave with the sample can start the sample on fire. The biggest error made with this method is that the samples aren’t dried for a long enough time. It should be dried until three weight measurements in a row are not very different. Then you take the first wet weight minus the final dry wet and then divide by the first wet weight-make sure you subtract the weight the container from the first wet weight and the final dry weight before you do this calculation. Multiple by 100 and that is your DM %. It is vital to use the same method every time you test a sample of silage otherwise you can’t compare the DM % numbers you get each time.

Click on the links below to read more about specific recommendations from extension publications.

Note: This method can also be used to find the moisture of hay, but read the publications below for proper sampling procedures.

Purdue http://www.agry.purdue.edu/Ext/forages/rotational/articles/PDFs-pubs/use-of-microwave-drying.pdf

Missouri http://extension.missouri.edu/publications/DisplayPub.aspx?P=G3151

Wisconsin http://www.uwex.edu/ces/crops/uwforage/CSMoistTest.htm

South Dakota State http://agbiopubs.sdstate.edu/articles/ExEx8077.pdf

Finally Dr. Mertens explained that ration the cow eats often is different than what the nutritionist recommends. Narrowing this gap between what the nutritionist recommends and what the cow eats is also an issue that needs to be addressed. A nutritionist will look at feed analysis numbers and formulate a ration for the farmer, then the farmer may modify the ration slightly, additionally the person feeding the cows may make changes, and finally the cow herself may sort the feed and not eat the ration in front of her.

To view Dr. Mertens’ PowerPoint presentation click here or on the title in italics.