Biomass yield and nutritive value of Stylosanthes scabra accessions as forage source for Goats

Abstract

Shortage of quality feed is the major constraint in livestock production, particularly under smallholder subsistence farmer s conditions in sub-Saharan Africa. Livestock production under smallholder subsistence farmers depends predominantly on communal grazed natural pastures, which are often inadequate in both quantity and quality, particularly during the dry season. In order to improve livestock production in these areas, shortage of feed must be addressed in terms of quantity and quality. Stylosanthes scabra (Vog.) accessions were evaluated for adaptability, agronomic performance, persistency and nutritive value in subtropical climate of Pretoria as potential forage source for ruminant animals. Several experiments (including field trials, laboratory experiment and stall feeding trials) were conducted at Hatfield Experimental Farm, University of Pretoria, South Africa. In the field trial, 15 accessions of Stylosanthes scabra were evaluated for adaptability and agronomic performance. The persistence of Stylosanthes scabra accessions under rain-fed conditions over three years showed their adaptability to the study area. However, three of the accessions, namely 9281, 11595 and 11604, were consistently superior in terms of biomass yield over the three-year period (2012 to 2014). Thus, from the biomass production point of view, these three accessions are recommended for future use as legume forage. Promising accessions identified in terms of adaptability and productive parameters were further evaluated for nutritive value parameters by determining their chemical composition, phenolic compound concentration, in vitro organic matter digestibility and in vitro gas production characteristics. Generally, the adaptable accessions have more than 17% DM crude protein (CP) content with relatively low neutral detergent fibre (NDF) ranging from 29.9 to 70.1% DM and very low total phenols ranging from 5.5 to 11.4 g kg-1 DM, total tannins ranging from 2.4 to 8.4 g kg-1 DM and total condensed tannins ranging from 0.3 to 3.4 g kg-1 DM. Thus, they were highly digestible with the range of 66 to 79%. This indicates that these accessions can be utilized as supplementary forage and nitrogen sources to complement poor-quality forage. Five Stylosanthes scabra, selected from the promising accessions, were in a preference and palatability study using Saanen goats. Generally, the five accessions were acceptable and palatable to goats. However, there was a significant (P < 0.05) difference in terms of intake and preferences. Accession 11604 was the most preferred, while accession 11255 was the least preferred. Five accessions that were used in palatability study were further used to evaluate their effect to poor-quality grass hay when supplemented at two levels (15% and 30%). The response to supplementation was measured by monitoring in vitro ruminal fermentation, associative effects and degradability of NDF. Supplementing poor-quality grass hay with Stylosanthes scabra accessions improved grass hay fermentation. This study showed that 30% supplementation level with accession 11604 led to a positive associative effect with grass hay and also improved NDF degradability. Consequently, this accession was recommended for future use as a forage supplement to poor-quality basal diet. The inclusion of Stylosanthes scabra forages in total mixed rations (TMR) for Saanen goats as a partial replacement of lucerne (alfalfa) forage did not significantly (P > 0.05) affect the nutritive value; nor did it affect the animals performance in terms of intake, nutrient digestibility and nitrogen retention. This means that Stylosanthes scabra can be used to partly replace alfalfa without compromising the nutritive value of the TMR diet. The overall outcome is that accession 11604 is recommended for use as supplementary feed resource. However, further study is required to determine suitable means of integrating this accession in the farming system in order to converts this forage into high-quality animal products (meat, milk, wool, etc).