Summary

Forage quality testing was completed on annual forages grown during 1998 and/or 1999. Included were spring cereals, legumes and summer annuals like sorghum and millets. Using a single cut harvest system when the majority of summer annuals had produced seed heads, crude protein (CP) was generally more than 8% and total digestible nutrients (TDN) more than 63% of dry matter. Annual legumes had 12 to 18% CP and more than 63% TDN. Pearl and irrigated foxtail millets had higher crude protein levels than sorghum forages, but nitrate levels were also higher. Some mineral contents varied by location and associated management.

Introduction

Results of forage production and quality comparisons of individual annual forage cultivars were presented in the 2001 Nebraska Beef Cattle Report, pp. 26-28. However, only one year of forage quality results (1998) was available at that time. The purpose of this report is to summarize quality results by forage crops rather than individual cultivars and to show the results from macro- and micro-mineral tests for 1999 crops grown on the high plains of western Nebraska or eastern Wyoming.

Procedure

Dryland and irrigated annual forage trials were conducted over two years (1998 and/or 1999) to update forage production and quality characteristics of cultivars of spring triticale, oat, barley, pea, vetch, soybean, forage sorghum, sorghum x sudangrass, sudangrass, pearl millet and foxtail millet. A single cut harvest system was used for each group when the majority of grass cultivars had produced seed heads or when the legumes had reached early bloom or pod-fill stages of maturity. Plots in Nebraska were planted in rows 12 inches apart with a double disc grain drill with a cone seed distribution system. Fertilizer was applied preplant or as a side-dress and legume seed was treated with inoculants. Nitrogen application rates were 45 to 60 lb per acre for dryland grass forages and 120 lb per acre for irrigated forages.

There were generally 4 to 7 replications of cultivars per trial. Forage samples were taken and chopped immediately after harvest with a plot swather and then dried for quality analyses at the USDA Forage Research Laboratory and the University of Nebraska Soil and Plant Analysis Laboratory in Lincoln, or sampled immediately for freezing and subsequent determination of ruminally undegradable intake protein (UIP) at the Ruminant Nutrition Laboratory in the University of Nebraska Department of Animal Science (1997 Nebraska Beef Report, pp. 38-39).

Forage quality tests were conducted using a combination of near infrared reflectance spectroscopy (NIRS) and wet lab chemistry analyses as suggested by the National Forage Testing Association or established against standard reference materials by the labs in Lincoln. Ruminally undegradable intake protein was determined on frozen and freeze dried forage samples that were suspended in nylon bags in the rumen of fistulated beef cattle fed a high forage diet. Mineral contents of the 1999 forage crops were determined by x-ray analysis. Results for all quality tests were expressed on a dry matter basis. Data were analyzed with the SAS General Linear Model.

Results

Forage quality results (Tables 1 and 2) include columns for UIP as a percentage of crude protein to indicate the ruminally undegradable portion that bypasses to the intestinal tract. There was considerable variation in the UIP values for most of the cultivars, but UIP was generally in a range of 5 to 10% of CP for the fresh-cut, growing annual forages tested. These values were slightly lower than UIP levels suggested by the National Research Council (1996) for fresh grass and legume forages.

Crude protein levels were similar among cereal and sorghum forages when they were harvested after the majority of the cultivars had produced seed heads. Irrigated foxtail millet was higher in CP and in nitrate nitrogen than the sorghum forages. However, irrigated foxtail millet was fertilized with 120 lb of N per acre, which was the same rate used for the taller growing summer annuals. This rate was too high for the foxtail millet, resulting in nitrate nitrogen values greater than 2000 ppm, a threshold level for toxicity concern in ruminants.

Although 1998 dryland foxtail millet was lost to poor stand, the 1999 dryland foxtail millet was lower in CP and nitrate nitrogen due to advanced maturity in a hot, dry growing season and nitrogen application limited to 45 lb of N per acre preplant. While pearl millet was higher in CP and nitrate nitrogen than sorghum forages, the highest levels among three cultivars were in a vegetative cultivar that would not mature and produce seed heads in the environments tested. Thus, variety, maturity and nitrogen management were factors in level of CP and nitrate nitrogen observed in these summer annuals.

Crude protein levels ranged from 12 to 18% of dry matter for soybean, pea and vetch forages when harvested at mid pod-fill (soybean) and early bloom stages of maturity (pea and vetch). Available energy levels for the legumes were similar to those for the cereal, sorghum and millet forages, averaging about 65% TDN. All energy contents were predicted from acid detergent fiber (ADF) by formulas suggested by the National Forage Testing Association and used by the University of Nebraska Soil and Plant Analysis Laboratory.

Forage mineral levels are shown in Tables 3 and 4 for most of the annual forages harvested in 1999. The differences in mineral levels for the same cultivars and crops grown at different locations were likely due to differences in dryland versus irrigated management, soil type, soil fertility, and cropping history. Means and standard deviations are provided for the contents of macroand micro-minerals that should be helpful in evaluating the mineral contributions from these annual forages to animal mineral requirements. For example, growing beef cattle weighing 660 lb and gaining 2 lb per day would require 0.36% Ca and 0.19% P in the dry matter of a diet containing 60% TDN. Cattle consuming irrigated sorghum and millet forages grown in this study could have met those requirements.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Elbert C. Dickey, Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.

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