The effect of temperature during processing of rape seed meal on amino acid degradation in the rumen and digestion in the intestine

Commercially processed rapeseed meals either untreated or treated at temperatures of 130, 140 and 150°C and moisture levels of 15 and 20% were used to measure protein and amino acid degradation in the rumen and digestibility in the intestine. Effects of these treatments were measured with nylon bag and mobile bag techniques using rumen and duodenal fistulated cows. For untreated rapeseed meals effective protein degradabilities were similar and about 73%, but for heat treated meals the degradability decreased to 56% for moderate heat treatment and to 15–23% for 140 and 150°C treatments. The 16 h rumen protein and amino acid degradabilities for untreated samples were similar; however, for heated samples, degradability of protein (averaged over moisture levels) was higher than for total amino acid nitrogen: 48.8 and 39.9%, 22.8 and 8.1%, and 20.1 and 4.5%, for samples heated to 130°C, 140°C and 150°C, respectively. Higher degradabilities of protein, total amino acid nitrogen and individual amino acids were found using 20% compared with 15% moisture. Intestinal digestibility of protein from rapeseed meal samples preincubated during 16 h in the rumen was on average 81% for samples heated to 130°C, 73% for unheated samples and 67% for samples heated to 140 and 150°C. A similar effect of heat treatment was found for intestinal digestibilities of total and individual amino acid nitrogen. Digestibility of intact protein in the intestine was similar for untreated meals and those heat-treated at 130°C and averaged 89%, but for samples heated to 140 and 150°C the digestibility was only 65–70%. The proportion of the protein digested in the intestine was higher for rapeseed meals treated at 130°C (38%) than for untreated meal (21%), and the total digestibility was unchanged, indicating that heat treatment at 130°C did not overprotect the protein and may shift the site of protein digestion from the rumen to the intestine.