Polyethylene glycol affects goats' feeding behavior in a tannin-rich environment

Abstract

High concentrations of condensed tannins in browse impair brush clearing by goats. We studied the effect of polyethylene glycol (PEG, MW 4000), a polymer that binds condensed tannins, on the feeding behavior of Damascus goats (Capra hircas) on a range dominated by tannin-rich lentisk (Pistacia lentiscus L.). This was done with or without a nutritious alternative to browse (alfalfa hay) available at pasture. In phase 1, no hay was provided to goats; in phase 2, hay was distributed daily in the field. In both phases, 6 goats had free access to PEG while at pasture, while 6 goats that grazed separately on another paddock did not.All goats received each night an allowance of concentrate (400 g day"' of 40% ground corn grain, 40% ground barley, 17% soybean meal and 3% of a mineral-vitamin premix, and contained as fed 16% crude protein (CP) and 2.66 Mcal kg"' of Metabolizable Energy). The 2 groups of goats alternated daily between paddocks. Goats supplemented with PEG spent more time browsing lentisk than goats in the control group (73 and 41%, respectively, P < 0.0001). Goats in the control group spent more time foraging on dry grasses than their PEG-fed counterparts (28 and 12%, respectively, P < 0.0001). Goats from the PEG group gained body weight at a higher rate than controls. The daily intake of PEG was 450 g, with an intake rate of 1.2 g sec-'. Supplemental alfalfa hay substituted partly for dry grasses in goats' diets, but did not modify the percent of time goats in either treatment spent browsing lentisk. Our data suggest that PEG has the potential to increase intake of tannin-rich species, even where alternative fodder of better nutritional quality is present. However, self-feeding of PEG may not be the best way to provide PEG because goats may ingest more PEG than needed to annul the aversive effects of tannins on food intake. Mcal kg' de energia metaboizable). Los 2 grupos de cabras se alternaron diariamente entre los potreros. Las cabras suplementadas con PEG pasaron mas tiempo ramoneando el " Lentisk" que las cabras del grupo control (73 y 41 %, respectivamente, P < 0.0001). Las cabras del grupo control pasaron mas tiempo apacentando zacates secos que las cabras suplementadas con PEG (28 y 12% respectivamente, P < 0.0001). Las cabras del grupo con PEG ganaron peso a una mayor tasa que las del grupo control. El consumo diario de PEG fue de 450 g con una tasa de ingestion de 1.2 g seg-l. La alfalfa suplementada substituyo parcialmente los zacates secos de la dieta de las cabras, pero no modifico el porcentaje de tiempo que las cabras de cualquier grupo pasaron ramoneando el " Lentisk" Nuestros datos sugieren que el PEG tiene potencial para incrementar el consumo de especies ricas en taninos, aun donde un alimento alternativo de mejor calidad nutritional este presente. Sin embargo, el autoconsumo de PEG puede no ser la mejor manera de suministrarlo porque las cabras pueden ingerir mas PEG del requerido para anular el efecto aversivo de los taninos en el consumo de alimento.