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 t emperatures of 130, 140 and 150 degrees C and moisture levels of 15 an d 20% were used to measure protein and amino acid degradation in the r umen and digestibility in the intestine. Effects of these treatments w ere measured with nylon bag and mobile bag techniques using rumen and duodenal fistulated cows. For untreated rapeseed meals effective prote in degradabilities were similar and about 73%, but for heat treated me als the degradability decreased to 56% for moderate heat treatment and to 15-23% for 140 and 150 degrees C treatments. The 16 h rumen protei n and amino acid degradabilities for untreated samples were similar; h owever, for heated samples, degradability of protein (averaged over mo isture 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 de grees C, 140 degrees C and 150 degrees C, respectively. Higher degrada bilities of protein, total amino acid nitrogen and individual amino ac ids were found using 20% compared with 15% moisture. Intestinal digest ibility of protein from rapeseed meal samples preincubated during 16 h in the rumen was on average 81% for samples heated to 130 degrees C, 73% for unheated samples and 67% for samples heated to 140 and 150 deg rees C. A similar effect of heat iii treatment was found for intestina l digestibilities of total and individual amino acid nitrogen. Digesti bility of intact protein in the intestine was similar for untreated me als and those heat-treated at 130 degrees C and averaged 89%, but for samples heated to 140 and 150 degrees C the digestibility was only 65- 70%. The proportion of the protein digested in the intestine was highe r for rapeseed meals treated at 130 degrees C (38%) than for untreated meal (21%), and the total digestibility was unchanged, indicating tha t heat treatment at 130 degrees C did not overprotect the protein and may shift the site of protein digestion from the rumen to the intestin e.