Abstract:
The search for alternative feed additives for ruminants became essential due to restrictions on the use of antibiotics and synthetic growth promoters in the livestock industry, as well as extensive pressure on the farmers to reduce methane emissions whilst maintaining production levels. Plant extracts showed some potential to use them as additives in the ruminant feed industry mainly due to their ability to act as rumen modifiers by means of their secondary compound’s activity. Secondary compounds may exert changes to the activities of the microbial population in the rumen, and such changes may lead to modifications of rumen fermentation characteristics and methane production. The aim of this study was to screen extracts from seven South African plant species for their potential to modify rumen fermentation charactertics using in vitro techniques. The plant species included in this study were Combretum erythrophyllum; Dodonaea viscosa; Heteropyxis natalensis; Sclerocarya birrea; Erythrina lysistemon; Searsia chirindensis and Halleria lucida. The plant extracts were first evaluated at a recommended dose level of 50 mg/kg DM for their effects on in vitro gas production (mL), methane production (mL), rate of gas production (mL/hr) and in vitro organic matter digestibility. Subsequently, the effect of dose level was evaluated by testing the seven plant extracts at 300 and 600 mg/kg DM. In the first study, where plant extracts were tested at a recommended dose level of 50 mg/kg DM, plant extracts from C. erythrophyllum, S. chirindensis and H. lucida significantly increased (P < 0.05) the rate at which gas was produced. In the second study, the seven plant extracts were tested at two higher dose levels of 300 and 600 mg/kg DM. When compared to the negative control, plant extracts from E. lysistemon, used at both 300 and 600 mg/kg DM dose levels, depressed the volume of gas produced after 4 hours of incubation. In contrast, plant extracts from S. chirindensis increased the volume of gas produced (P < 0.05) at a 300 mg/kg DM dose level at 4-, 8-, and 12- hours of incubation and at a 600 mg/kg DM dose level at 8- and 12 hours of incubation. The IVOMD values were not significantly (P > 0.05) affected by plant extract treatments when applied at a dose level of 50 mg/kg DM or at either 300 or 600 mg/kg DM dose levels. Therefore, results from these two studies indicate that plant extracts from the species C. erythrophyllum and H. lucida when used at 50 mg/kg DM dose level, and plant extract from S. chirindensis used at either 50 or 300 mg/kg DM dose levels showed good potential as additives in ruminant diets to improve the rate of gas production of poor-quality roughage-based diets which may improve energy availability to the ruminant. However, further studies are recommended to refine the optimal dose rate of these plant extracts for the purpose of reducing methane production without negatively altering the digestibility and the volume of gas produced.
