Feed cost is one of the largest expenses on dairy farms. In addition to being a major cost, over feeding, under feeding or feeding an improperly balanced diet can impair cow health, decrease milk production, and result in negative environmental impacts. Regular dry matter (DM) testing of feeds and rebalancing the ration to compensate for DM changes ensures that dairy producers are feeding the ration formulated by their nutritionist. Where trade names appear, no discrimination is intended, and no endorsement by Penn State Extension or by the author is implied.
Frequency and Methods of Dry Matter Determination
The frequency at which dairy farms test forages for DM varies from farm to farm. Penn State recommends weekly testing of silage DM. While some test this frequently, many dairy farmers or their nutritionists will test once or twice a month. Less frequent testing results in a greater chance of missing a change in silage DM and an improperly formulated ration.
The most common methods of on-farm DM analysis are using a Koster tester or microwave oven. Either of these methods will work, but they can take 20 to 30 minutes and must be monitored to make sure the samples are not over heated.
Near Infrared (NIR) Analysis
Near-infrared technology has been used in commercial laboratories to analyze feed and other agricultural products for years. NIR measures the light (in the near-infrared spectrum) reflected off of a sample of interest when analyzed in a spectrophotometer. NIR is faster and lower cost than using traditional wet chemistry methods to determine the nutritional composition and DM of feeds.
Only recently has NIR technology been applied to an on-farm setting. On-farm systems work similarly to NIR used in a lab setting; a feed sample is put in front of a scanner, the scanner analyzes the feed sample, and the result is returned to the farmer or nutritionist who then can make management decisions regarding the feed.
On-farm NIR greatly decreases the amount of time it takes for a farmer to receive information about the composition of feed being fed to his dairy cows. Traditional wet chemistry methods of feed analysis often take a week or more from the time the sample is collected to the time the results are returned to the farmer or nutritionist. With laboratory NIR the turnaround time from when a sample is collected to the time the results are back can be decreased to a few days. With on-farm NIR results are returned instantly to the farmer, allowing management decisions to be made on the spot.
Application of On-farm NIR Analysis
Figure 1. Dinamica General NIR analyzer mounted in skid loader bucket.
One on-farm NIR system available is the Dinamica General precisionFEEDING system. This system utilizes an NIR analyzer mounted in the bucket of the tractor (Figure1). Each time feed is scooped into the bucket the analyzer scans the feed and the amount of feed needed to be added to the mixer is adjusted based on the DM content of the feed. Samples are also analyzed for crude protein, NDF, ADF, ash, fat, and starch (Figure 2).
Figure 2. Daily variation in corn silage nutrient composition, as measured by the Dinamica General NIR analyzer.
Figure 3. Daily variation in corn silage DM, as measured by the Dinamica General NIR analyzer.
Dry matter content of corn silage can vary widely from day to day, as demonstrated in Figure 3. While the average of these readings would be around 32 or 33% DM, the range went from as low as 25% DM to as high as 41% DM over the six months shown here. Much of the variation in DM content, especially the very low readings, is likely related to precipitation events. By adjusting the ration on the spot, cows receive a more consistent ration from day to day and feed waste can potentially be reduced.
As an example, if a ration calls for 50 pounds of corn silage on an as-fed basis and DM is assumed to be 33%, 16.5 pounds of corn silage DM will be fed. For each one-point deviation of the actual %DM from the assumed %DM the dairy farmer will over or under feed 0.5 pounds of corn silage per cow per day. If the actual DM of the corn silage is 28% the cows will only receive 14 pounds of corn silage on a dry matter basis.
An Italian study compared dairy farms using on-farm NIR systems (dg precisionFEEDING System) with farms not using the system (study summary). In this study, feed costs were $0.09 per cow per day less and milk production was 5.6 pounds more per cow per day (65.9 vs. 71.5 pounds/cow per day) on farms using the NIR system than on farms not using the system. For a 200-cow dairy this would result in approximately $73,584 of increased revenue from milk sales (assuming $18/cwt milk) and a $6,570 savings in feed cost per year. Increased production was attributed to a more consistent ration being delivered to the herd. Lower feed cost was attributed to being able to feed more precisely to the needs of the herd and thus decreasing feed waste. The study also reported an improvement in the general health of the herd, based on changes in blood parameters and a reduction in mastitis.