Performance of sheep and goats fed Arctostaphylos canescens with and without polyethylene glycol supplementation.
Arctostaphylos canescens Eastw. is considered an important element in the chaparral fire matrix and an invasive plant in coniferous forest plantations in California. Previous studies reported that dry matter intake of Arctostaphylos was low, presumably because of its low nutritional quality and high condensed tannin (CT) content. We hypothesized that intake and digestibility of Arctostaphylos could be increased by the provision of a tannin-complexing agent polyethylene glycol (PEG). This study determined the effects of PEG (MW 4000) supplementation on intake (I) and digestibility (D) of Arctostaphylos in goats and sheep. Polyethylene glycol was added to drinking water at four levels (0.3%, 0.15%, 0.05%, and 0%) of body weight (BW). Alfalfa pellets were used as diet supplement at 1.5% of BW. Nutritional quality of Arctostaphylos was low as compared with alfalfa pellets. Arctostaphylos crude protein (CP) levels were low (4.5% vs. 17.9%) and CT concentration was high (23.1% vs. 0%), whereas estimates of in vitro organic matter digestibility (OMD, 36.6%) and metabolizable energy (5.1 MJ.kg-1 dry matter [DM]) in Arctostaphylos were almost half of those found for alfalfa pellets (70.3% and 9.5 MJ.kg-1 DM). A curvilinear increase (P<0.05) in nutrient intake (per g.d-1 and per kg BW0.75) was observed in goats and sheep as PEG levels increased, although a linear increase (P<0.001) was observed in CP intake (g.d-1) of Arctostaphylos by goats. Addition of PEG curvilinearly increased (P<0.05) digestibility of DM, CP, and neutral and acid detergent fiber, but quadratically increased (P<0.05) that of OM in goats and sheep. Incorporation of PEG in drinking water at the level of 0.15% BW in sheep and goats was effective to maximize inactivation of CT in Arctostaphylos. However, the success in adopting this practice as a useful tool in vegetation management programs will depend on the cost-benefit ratio.