Effects of different doses of gamma irradiation on ruminal degradability and type of escaped protein of corn grain

This study was carried out to determine effects of gamma irradiation on ruminal crude protein degradation of corn grain and its escaped protein type by using nylon bags and SDS-PAGE techniques. Duplicate nylon bags of untreated or irradiated corn grain at dose of 25, 50 and 75 kGy were suspended in the rumen of four non-lactating Holstein cows for 2, 4, 6, 8, 12, 16, 24 and 48 h. Intestinal crude protein digestibility was measured using mobile nylon bag technique. Degradation parameters and effective degradability of crude protein were calculated by fitting data to a non-linear equation. Means were separated using orthogonal contrast for detecting linear, quadratic and cubic relationships. Gamma irradiation decreased linearly (p<0.001) washout fraction, had cubic effect (p<0.01) on potentially degradable fraction, and decreased linearly (p<0.001) effective degradability of crude protein. Electrophoretic analyses of untreated corn grain revealed that two zein subunits remained in bags evenafter 48 h of incubation and the main part of escaped protein was zein subunits. At zero incubation time, large amount of albumin and globulin were disappeared, but in gamma irradiated corn grain, these subunits were remained in bags in the latest incubation period. In irradiated samples, most part of escaped protein was two subunits of zein and globulin fractions. Gamma irradiation increased intestinal digestibility of crude protein and its effect was linear. Based upon these results, gamma irradiation appeared to be effective in decreasing ruminal protein degradability and increasing intestinal protein digestibility.