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Comparison of Nitrogen Solubility in Three Solvents to In Vitro Protein Degration of Heat-Treated Cottonseed Meal¹

Department of Animal Science, Texas A & M University, College Station 77843

ABSTRACT

Solubility of nitrogen in McDougall's buffer, 10% Burroughs' buffer, and .02 N sodium hydroxide was measured on samples of autoclaved and commercial cottonseed meal. Abilities of solvents to solubilize nitrogen were compared to ruminal protein degradation previously estimated by an in vitro procedure. Generally, solubility of nitrogen in all three solvents decreased with increased heat-treatment. Nitrogen extracted by .02 N sodium hydroxide was consistently greater than that extracted by the buffer solutions. With autoclaved meals, nitrogen solubilities in .02 N sodium hydroxide and McDougall's buffer were 2.2 to 5.6 and 1.1 to 1.9 times greater than in Burroughs' buffer. Linear regression equations were developed by regressing observed degradation on nitrogen solubilities for the autoclaved cottonseed meals. Degradation was more highly correlated with nitrogen solubility in .02 N sodium hydroxide than in McDougall's and Burroughs' buffers (coefficient of determination = .98 versus .84 and .64, respectively). These regression equations were used to predict degradation of commercial cottonseed meals. Mean differences between predicted and observed degradation were 5.4, 6.7, and 12.9 percentage units for .02 N sodium hydroxide, McDougall's buffer, and Burroughs' buffer. More realistic estimates of ruminal protein degradation were obtained from nitrogen solubilities in .02 N sodium hydroxide and McDougall's buffer than in Burroughs' buffer.

¹ Technical article 16393 of the Texas Agricultural Experiment Station, College Station 77843.

² US Dairy Forage Research Center, 1925 Linden Drive West, University of Wisconsin, Madison 53706. To whom correspondence should be addressed.