Content area
Abstract
Two trials were conducted to evaluate the validity of acid detergent insoluble nitrogen (ADIN) as an indicator of indigestible nitrogen. In Trial 1, eight non-forage plant protein sources were treated to produce heat-damage. Apparent nitrogen digestibilities were reduced in all sources by heat treatment; however, ADIN analysis underestimated nitrogen digestibility. In Trial 2, seven dried distillers grains were evaluated for nitrogen digestibility. Although the ADIN contents varied among feeds, no differences were observed in nitrogen digestibility. It appears ADIN in non-forage protein sources predicts more damage than what was indicated by in vivo nitrogen digestibility.
Four studies were conducted to evaluate growth efficiency and nitrogen digestibility of heat-damaged protein. In Trial 1, corn gluten meal (CGM), control (CGM-C) or heat-damaged (CGM-H), was fed to lambs at 5 levels along with a urea control. Gain averaged 43 g/d for lambs fed the urea control and 118 and 86 g/d for those fed the highest level of CGM-C and CGM-H. The heat-damage in CGM depressed protein efficiency by 46%. In Trial 2, nitrogen digestibility of CGM was depressed 22% by heat-damage. Depression in protein efficiency was twice the depression in nitrogen digestibility of heat-damaged CGM. In Trial 3, dried distillers grains (DDG), control DDG (DDG-C) or heat-damaged DDG (DDG-H), were fed to cattle at 5 levels along with a urea control. Gain for cattle fed the urea control was.40 kg/d, whereas the highest levels of DDG-C and DDG-H produced.84 and.72 kg/d. Protein efficiency of DDG was depressed 34% by heat-damage. In Trial 4, nitrogen digestibility of DDG fed to cattle was only depressed 7% by heat-damage. These data suggest that some of the nitrogen in heat-damaged protein was absorbed post-ruminally but was not used for growth by growing ruminants. The depression in animal performance by heat-damaged protein appears to be due to the reduction in metabolizable lysine content of these feeds.
