<I>In vitro</I> degradability and gas production parameters of Sericea lespedeza (<I>Lespedeza cuneata</I>) mixed with varying types and levels of roughages

Abstract

Sericea lespedeza (Lespedeza cuneata) regrowth was harvested at early (ELP) or late (LLP) flowering stages, mixed with varying types and levels of roughage and fermented for 72 h in vitro, using the gas production (GP) technique. The roughage : lespedeza ratios were 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. The roughages included maize stover harvested at grain milk (MM) or dry (MD) stages and veld grass hay (GH). The crude protein (CP) content of ELP, LLP, MM, MD and GH were 187, 97, 48, 29 and 34 g/kg dry matter (DM), respectively. The corresponding NDF values were 283, 589, 696, 73.3 and 665 g/kg DM. Degradability was slightly higher in MM as compared to MD and GH (means 704.9 vs. 676.6 and 685.0 g/kg, respectively) between ELP rations. The roughages had similar but lower degradability in LLP rations (means 633.4, 632.6 and 631.1 g/kg for MM, MD and GH, respectively). Increased proportion of ELP and LLP resulted in decreased degradability in all the roughages. Microbial yield was similar among roughages in ELP rations, but the roughages differed in microbial yield among LLP rations whereby GH had the highest value and MD the lowest. Increased proportion of ELP elicited an increase in microbial yield but increasing LLP had no effect (range 135.0 – 264.8 g/kg among ELP and 143.4 – 295. 9 g/kg among LLP rations). Roughage type affected GP with MD and GH having the lowest and highest values, respectively. The values ranged from 167.4 – 209.8 and 160.4 – 221.0 mL among ELP and LLP rations, respectively. There was a decrease in GP as the proportion of ELP or LLP increased and roughage type x supplement level interaction had effect. The ratio of degradability to GP, i.e. the partitioning factor (PF) ranged from 3.43 – 4.74 and 3.13 – 4.23 among ELP and LLP rations, respectively, whereby GH had highest and MD lowest values. The rate of GP from soluble fraction was not affected, but that of the fibre fraction differed among the roughages in ELP rations whereby GH had lower rate than MM and MD (mean 0.023 vs. 0.026 and 0.025, respectively). The lag time (lt) tended to be reduced as ratio of ELP increased (range 1.83 to 6.59 h). In LLP rations, roughage type, supplementation level, roughage type x supplementation level interactions affected lt. The GH had the longest and MM had the shortest lt among the roughages (range 0.88 – 9.61 h), and likewise lt reduced as ratio of LLP increased. The results indicate that the various nutritive attributes considered are differentially influenced by lespedeza type and level, roughage type and the interactions among these aspects, hence the importance of their implications in formulating ruminant diets. The results indicate that when using roughages with similar quality as those studied, lespedeza ratio of 40 - 60% of DM consumed can be beneficial.

South African Journal of Animal Science Vol. 36(2) 2006: 111-121