Development of a Novel System to Estimate Protein Degradability in Legume and Grass Silages

¹ Department of Dairy Science, University of Wisconsin, Madison 53706
² Department of Soil Science, University of Wisconsin, Madison 53706
³ Department of Agronomy, University of Wisconsin, Madison 53706

Five trials were conducted to develop a system to estimate rumen-undegradable protein (RUP) of legume and grass silages using near infrared reflectance spectroscopy. In situ procedures were the reference method used to determine silage RUP content. Trials 1, 2, and 3 were devoted to improving in situ procedures. In trial 1, alfalfa silage with and without heat treatment was incubated ruminally in 30 cows. The standard deviation of in situ RUP attributable to cow and diet was 0.82 and 3.80 g/10^–1 kg of crude protein (CP) for the unheated and heated alfalfa, respectively. Based on trial 1, it was determined that 8 cows would be required to establish RUP standards. In trial 2, low (13.3 g/10^–1 kg of CP) and high (44.5 g/10^–1 kg of CP) RUP standards were developed using eight ruminally cannulated cows.

In trial 3, 11 new RUP standards were developed by mixing trial 2 RUP standards together. The RUP standards were used to employ a calibration curve technique in ruminally cannulated cows. The technique was employed in four ruminally cannulated cows to estimate RUP contents of 121 silages, and RUP values were used for near-infrared reflectance spectroscopic analysis in trial 4. Trial 4 procedures yielded a calibration for RUP content of silages with an R² of 0.84 and a standard error of calibration of 1.55 g/10^–1 kg of CP. In trial 5, the equation was tested on 300 silage samples. The mean predicted RUP content was 21.8 g/10^–1 kg of CP. Data suggest near-infrared reflectance spectroscopy can predict RUP content of silages.

Key Words: silages • in situ • protein degradation • near-infrared

Submitted on July 13, 1998
Accepted on November 23, 1998

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