Phenolics in Southern African Browse Species.

In semi-arid northern South Africa, low forage quality throughout the dry season and anthelmintic-resistant gastrointestinal nematodes (GIN) limit ruminant productivity.  Plants containing biologically active protein precipitable phenolics (PPP), compounds that characteristically bind and precipitate proteins, can improve ruminant nutrition by binding to plant proteins in the rumen and preventing microbial degradation, thereby increasing amino acid flow to the small intestine.  These PPP may also increase animal resistance to GIN infections.  We evaluated foliage from Limpopo Province browse species that maintained leaves during the dry season: Acacia caffra (hook-thorn; HT), A. karoo (sweet thorn), Burkea africana (wild seringa; WS), Combretum zeyheri (large-fruited bushwillow), C. molle (velvet bushwillow; VBW), Terminalia sericea (silver cluster-leaf; SCL), and Searsia lancea (karee).  Leaves were collected in August 2012 during the dry season and January 2013 during the wet season and were analyzed for crude protein, PPP concentrations, and the amount of protein bound (PB) by PPP.  Crude protein concentrations ranged from 7.1-18.3%, indicating the species should meet minimum ruminant maintenance protein requirements in the dry season when forage quality is often poor.  Protein precipitable phenolic concentrations ranged from 64.7-229.3 g kg^-1 DM, and the amount of PB by PPP ranged from 121.6-169.1 g kg^-1 DM.  Changes in amounts of PB by PPP from the dry to wet season varied by species, as PB exhibited no change (P≥0.01) in some species, increased (P≤0.01) in others, and decreased (P≤0.01) in WS.  Protein precipitable phenolic concentrations were at least 27% lower (P≤0.01) in the dry than wet season for HT, SCL, and VBW, suggesting PPP-associated benefits could be reduced in ruminants consuming these three species during the dry season.  Results warrant further examination of browse species important in rangeland ruminant production systems with extended dry seasons.