Evaluation of Optigen II® as a Source of Rumen Degradable Protein for Mature Beef Cows

Cattle consuming bahiagrass pastures in Florida are often deficient in crude protein. The purpose of this study was to observe the effects of two protein supplements (Urea and Optigen) as compared to cows receiving no protein supplementation (Control) while consuming bahiagrass hay. Optigen II® (Alltech, Inc., Nicholasville, KY) is a slow-release nitrogen source. The delayed availability of nitrogen associated with this product was hypothesized to synchronize with the availability of energy from the lowquality forage, thereby increasing dry matter intake and cow performance. Bodyweight and body condition score were recorded on three sampling dates (March ‘06, April ‘06, May ’06), and blood samples were collected to be analyzed for blood urea nitrogen and blood glucose concentrations. Rumen samples were also collected on these sampling dates to determine rumen fluid pH. Dry matter intake was recorded daily. There were no differences between the three treatments in dry matter intake (mean at week 8=18.67 lb, P=0.94), dry matter intake as a percent of bodyweight (mean at week 8 = 1.65, P=0.86), blood glucose concentration (mean=80.3 mg/dL, P=0.88), or cow body condition score (mean=5.24, P=0.81) at the completion of the study. Supplement type had an effect on mean rumen pH (control > Optigen, P<0.05) and blood urea nitrogen on d 28 and 56 (nitrogen supplements > control, P<0.001). INTRODUCTION Bahiagrass pasture generally contains about 9% crude protein (CP) or less on a dry-matter basis. Many cows are not capable of consuming enough low-quality forage to satisfy their maintenance requirement for CP. Therefore, it is important for producers to implement a protein supplementation strategy for their cows, particularly for cows and heifers that have additional requirements for gestation, lactation, and growth. Protein sources may be classified by their relative amounts of rumen degradable protein (RDP) and rumen undegradable protein (RUP). Supplementation of RDP has been shown to positively affect cattle performance, forage dry matter intake (DMI), and forage digestibility. Urea may be used as a source of RDP (281% CP), which provides the nitrogen required by rumen microbes without adding to the bulk-density of the diet. This free space created can then be utilized to provide additional energy or other nutrients to meet or supplement cattle requirements. However, too much urea in the diet (>15% of total RDP) can lead to decreased performance compared with lower levels of urea supplementation. This decrease in performance in cattle consuming lowquality forages and urea is likely the result of the asynchrony of ruminal ammonia and digestible energy in the overall diet. The release of nitrogen in the rumen from urea is near instantaneous, while the release of energy from low-quality forages is not as readily available. Matching a slowrelease energy source with slow-release nitrogen should provide a more consistent supply of digestible nutrients in the rumen, avoiding sharp peaks of a single nutrient and improving diet utilization efficiency.