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In situ determination of protein degradation and metabolizable protein and amino acid requirements for growing beef cattle
Abstract
In situ studies were undertaken to investigate sources of error associated with estimates of bypass protein. Two trained technicians obtained similar estimates of escape protein (P $>$.3) when polyester bags were incubated 16 h in situ. No differences were observed among secondary rinsing methods (P $>$.1) indicating the method requiring the least amount of time and water to rinse each bag was adequate. Estimates of escape protein increased 5.5% (P =.02) for ice water soaked bags compared to controls implying an increase in microbial residue. Estimates of escape protein were 16% greater for machine rinsed bags compared to hand rinsed bags suggesting incomplete removal of ruminal contaminants. Four collaborative trials investigated an in situ procedure to evaluate the variation in estimates of escape protein among eight research institutions. Estimates of escape protein, expressed as a percent of crude protein and dry matter, varied per trial. A video tape demonstrating the procedure complimented a written procedure by reducing the error associated with location. Sieving the forage material did not reduce the variation in escape protein estimates compared to non-sieved material (P $>$.2). Representing the variances of location, trial, animal, and day as a percent of the total variance indicated most of the error was associated with technician which could be reduced with proper training. Requirements for metabolizable protein and amino acids were developed from 543 steers out of a database summarizing eleven trials where all animals were individually fed high forage diets supplemented with natural protein. The mid-trial weight for all animals was 253 kg with a range in initial to final weight of 200 to 316 kg, respectively. Daily gain ranged from $-$.04 to.89 kg/d. Metabolizable protein requirements of 3.8BW$\sp{.75}$ for maintenance (g/d) and 305 g/kg of live weight gain (r$\sp2$ =.69) were provided by weighted regression analysis. Amino acid requirements were calculated and expressed as a percent of metabolizable protein. A constant metabolizable protein requirement for gain suggests the efficiency for protein use is dependent upon both animal weight and rate of gain change.
Subject Area
Livestock|Agronomy
Recommended Citation
Wilkerson, Victor Allen, "In situ determination of protein degradation and metabolizable protein and amino acid requirements for growing beef cattle" (1992). ETD collection for University of Nebraska-Lincoln. AAI9225500.
https://digitalcommons.unl.edu/dissertations/AAI9225500