Microbial degradation of mimosine in goats

Abstract

An investigation was carried out to find out the extent of in vitro microbial degradation of pure mimosine (T1) and that of immature leaves (T2), mature leaves (T3), tender stems (T4) and seeds (T5) of L. leucocephala using strained rumen liquor obtained from three rumen fistulated Saanen – Malabari crossbred goats maintained under standard conditions of feeding and management. The proximate chemical composition and mimosine content of different edible parts of leucaena during the months of May, June and July were determined. While immature leaves and seeds had higher crude protein content, seeds had higher crude fat, tender stems had higher crude fibre and mature leaves had higher ash content compared to other edible parts of subabul. The average mimosine concentrations of T2, T3, T4 and T5 were 12.11 + 0.05, 4.89 + 0.02, 3.90 + 0.04 and 10.70 + 0.08 per cent respectively during May; 11.66 + 0.06, 5.23 + 0.03, 3.62 + 0.03 and 10.44 + 0.05 per cent respectively during June and 9.96 + 0.05, 4.92 + 0.03, 3.73 + 0.02 and 9.51 + 0.04 per cent respectively during July on a dry matter basis. The average mimosine concentrations of strained goat rumen liquor incubated with 37.50 mg/100 ml of added mimosine in pure form or as immature leaves, mature leaves, tender stems and seeds showed significant reduction at every 12 hr intervals from 0 to 48 hr of incubation, the final average concentrations being 23.98 + 0.37, 23.14 + 0.37, 22.20 + 0.28, 23.12 + 0.52, 23.35 + 0.37 mg/100 ml of SRL. The percentage of in vitro degradation in respect of T1, T2, T3, T4 and T5 increased significantly at every 12 hr intervals of incubation from 0 to 48 hr, even though the degradation was incomplete with all treatments, the average percentage degradation at 48 hr of incubation being 31.69 + 1.02, 34.49 + 1.18, 37.12 + 0.99, 34.54 + 1.50 and 33.41 + 1.03 respectively. The overall average rate of disappearance of mimosine in µg.ml-1 . h-1 in respect of T1, T2, T3, T4 and T5 for the entire period of 48 hr of incubation were 2.33, 2.54, 2.74, 2.54 and 2.44 respectively with highest rates during 0 to 12 hr, lower rates during 24 to 36 hr and least rates during 36 to 48 hr. The production of ammonia and VFA coincided with the active degradation of mimosine, there being faster degradation upto 12 hr of incubation with highest concentrations of ammonia and VFA at 12 hr of incubation. The overall results indicated that the rumen microorganisms of crossbred goats degrade mimosine to DPH, ammonia and VFA and that mimosine does not inhibit the microbial activity, even though the possible role of leucaena endogenous enzymes in the partial degradation of mimosine recorded in the present study cannot be ruled out.