Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 14, 2007
Publication Date: November 19, 2007
Citation: Phillips, W.A., Starks, P.J., Glasgow, S., Coleman, S.W. 2007. Different methods of estimating crude protein concentration of bermudagrass pastures for stocker calf production. Professional Animal Scientist. 23:696-701. Interpretive Summary: Performance of calves grazing warm-season grass pastures is usually reduced during the last half of the summer as compared to the first half, because as the plant matures the concentration of protein in the plant falls below the dietary nutrient requirement needed to maintain animal growth. Providing supplemental protein to calves during the last half of the summer grazing season can increase animal performance, but knowing when to begin supplementation is difficult. The most efficient supplementation strategy for stocker calf enterprises is to monitor forage protein content and to begin supplementation when forage crude protein concentration falls below the nutrient requirement for the targeted rate of animal gain. The objective of this experiment was to compare estimation of protein concentration of bermudagrass pastures derived from remote sensing of standing green biomass using spectral reflectance measurements versus more traditional methods. The remote sensing procedure used in this experiment provided accurate estimates of protein concentration in a more timely manner than traditional methods. As a result, producers could monitor the protein status of pastures more frequently, could more precisely pinpoint when to begin supplementation, and more efficiently use expensive protein supplements.
Technical Abstract: Providing supplemental protein during the last half of the summer grazing season to stocker calves grazing warm-season grass pastures can increase animal performance. The most efficient supplementation strategy for stocker calf enterprises is to monitor forage crude protein (CP) content and to begin supplementation when forage CP concentration falls below the nutrient requirement for the targeted gain. The objective of this experiment was to compare estimation of CP concentration of bermudagrass pastures derived from remote sensing (RS) of standing green biomass using spectral reflectance measurements, and estimations derived from near infrared reflectance spectroscopy (NIRS) analysis of fecal samples. Plots (1.6 ha) of Midland, Ozark, World Feeder and an experimental hybrid (74X12-12) bermudagrass were used. One plot of each variety was randomly assigned to NIRS analysis of feces (FNIRS) or RS of standing biomass (RS). Both FNIRS and RS methods of estimating forage CP concentration signaled that CP had dropped below our target level of 7% at similar (P = 0.86) points in the grazing season. In comparison to laboratory analysis, the RS method ranked the 4 varieties for CP concentration at the beginning of the grazing season better than FNIRS. A decrease in CP concentration during the first 6 weeks of the grazing season was detected by RS and FNIRS methods, but the accuracy was dependent upon variety. Based on these data, we concluded that RS and FNIRS can be used to determine when to initiate supplementation of beef calves grazing bermudagrass pastures and that timing of supplementation has dramatic impact on profitability of the enterprise.