Building beef cow nutritional programs with the 1996 NRC beef cattle requirements model

Area of Science:

• Animal Science
• Nutritional Biochemistry
• Ruminant Nutrition

Background:

• Designing effective cow-calf nutritional programs necessitates understanding nutrient requirements, diet quality, and intake.
• The 1996 National Research Council (NRC) beef cattle requirements model (1996 NRC) requires specific data on degradable intake protein (DIP) and microbial efficiency for accurate predictions.

Purpose of the Study:

• To establish a framework for generating data applicable to the 1996 NRC model.
• To characterize seasonal nutrient variations in native range and subirrigated meadow forages.
• To utilize the 1996 NRC model to predict nutrient balances in cattle grazing these forages and provide recommendations for its application.

Main Methods:

• Collected extrusa samples over two years from native upland range and subirrigated meadow in the Nebraska Sandhills.
• Analyzed samples for crude protein (CP), in vitro organic matter digestibility (IVOMD), and DIP.
• Developed regression equations to predict nutrients and used the 1996 NRC model to assess nutrient balances.

Main Results:

• CP and IVOMD showed rapid increases in early spring (March-April) on subirrigated meadows and increased from April to June on native range, followed by a decline from August to September.
• Degradable intake protein (DIP) trends mirrored CP fluctuations on both forage types.
• The 1996 NRC model accurately predicted nutrient balances when IVOMD was converted to digestible energy (DE) using the equation (1.07 x IVOMD - 8.13); otherwise, it yielded unrealistic net energy for lactation (NE(m)) balances.

Conclusions:

• Effective use of the 1996 NRC model for forage-fed cattle hinges on accurate estimates of DIP, microbial efficiency, and total digestible nutrient (TDN) intake, emphasizing the importance of seasonal forage nutrient data.
• Further research is recommended to improve laboratory methods for DIP estimation, develop reliable microbial efficiency indicators, enhance TDN prediction for forage diets, validate DIP and metabolizable protein (MP) requirements, and incorporate nitrogen recycling estimates.