Effects of microwave or infrared radiation on protein ruminal degradation and in vitro intestinal digestibility in feedstuffs

Microbial crude protein ( MCP ) is the main source of amino acids ( AA ) in the small intestine, followed by rumen undegraded protein ( RUP ). Due to limited MCP synthesis and increased AA demand in high-producing ruminants, strategies to enhance intestinal protein availability are relevant. This study evaluated the effects of thermal processing on six protein-rich feedstuffs: soybean meal, wheat bran, cottonseed meal, corn gluten feed, whole cottonseed, and whole soybean seed. A preliminary trial using soybean meal determined optimal processing times based on ruminal degradability curves. Two mathematical models (exponential and broken-line) were evaluated to determine optimal processing times for each thermal treatment. Based on the mathematical modeling performed in the preliminary trial, 30 minutes was selected for microwave treatment ( MW30 ) and 92 minutes for infrared radiation ( IR92 ). These time points were then applied to the remaining ingredients. These time points were then applied to the remaining ingredients. After processing, samples were incubated in situ for 16 hours in rumen-cannulated cattle, followed by in vitro intestinal digestibility ( ID ) assays. Crude protein and dry matter were analyzed, and the total protein available for absorption in the small intestine was estimated. Data were analyzed using a 6 × 3 factorial design with the GLIMMIX procedure in SAS. Whole soybean seed treated with IR92 showed the highest absorbable protein (85%), followed by whole cottonseed processed with MW30 (73.5%). Soybean meal also responded positively to both treatments, particularly IR92 (78%). Cottonseed meal showed moderate improvements, whereas corn gluten feed exhibited reductions in absorbable protein under both treatments. Wheat bran showed a negative response to MW30 but a modest improvement under IR92. Overall, the results indicate that infrared processing is more efficient for soybean-based ingredients, while microwave heating tends to be more advantageous for cotton-derived feeds, reinforcing the need to match processing conditions to ingredient-specific characteristics.