|Defining Forage Variability in
Project Leader and Principal UC Investigators
Glenn Nader, livestock farm advisor, UC Cooperative Extension Butte/Sutter/Yuba Counties
Creating a viable market for rice straw as livestock feed took another step
closer to reality in research conducted in cooperation with 21 Sacramento
Valley farmers last year.
This project evaluated treated and untreated straw at five locations with straw samples grown in Colusa, Glenn, Sutter and Yolo counties. In the first phase of the research, straw was treated with a macerator as rice was harvested - about 65 percent moisture. Maceration mechanically crimps the straw, which increases the speed of drying and theoretically improves digestibility for livestock. Macerated straw was windrowed, baled and then analyzed in a lab for standard measures of digestibility - crude protein, fiber content, fat content and dry matter. The study also investigated previously observed variations in rice straw from 38 different fields.
Results show that while rice straw is viable as a feed supplement, a great deal of variability exists among different sources and therefore not all straw should be fed to livestock without following guidelines. Crude protein must test at 4.5 percent or higher, while fiber, as measured by ADF (acid detergent fiber), must be 50 percent or lower. According to project leader and UC Cooperative Extension Farm Advisor Glenn Nader, this is essential to overcoming the stigma of failed attempts to feed rice straw to cattle.
In a survey of 38 samples, only 31.4 percent met the guidelines and three samples should not have been fed to cows at all. A high fiber percentage will cause straw to break down too slowly and not allow the cattle to consume enough to meet daily dietary requirements. Researchers also suspect there may be a year effect on protein levels, as they tested lower than they had previously.
Researchers also made adjustments to the mathematical model used to predict straw performance. The equation currently used to analyze most alfalfa hay samples as a measure of total digestible nutrients (TDN) is the Western states model. It tends to overvalue poor quality rice straw and undervalue high quality rice straw. The adjustments proved extremely accurate and will be verified with additional tests in 2004.
Over the course of this study, researchers also discovered elevated levels of manganese in some straw samples. Eight of 21 samples from 2002 work had manganese amounts over 1,000 ppm, a level that previously had been reported toxic to cattle. Excessive manganese inhibits cattle's ability to absorb copper, which in turn can lead to a variety of physiological problems. Further nutritional analysis concluded, however, that high manganese levels in rice straw do not pose a health risk to cows.
More information on feeding rice straw to cattle can be obtained from a free UC publication, Feeding Rice Straw to Cattle, located on the Web at http://anrcatalog.ucdavis.edu/pdf/8079.pdf.