Use of n-alkanes to estimate seasonal diet composition and intake of sheep and goats grazing in California chaparral

摘要

Small ruminants are increasingly used in prescribed grazing to reduce biomass in wildfire-prone plant associations. The objective of the study was to determine intake, botanical composition of intake, and nutritional quality of diets of sheep and goats browsing California chaparral during fall, spring and summer. Woody plants constituted 93.3%, 87.0%, and 88.8% of the diet of goats, and 93.7%, 67.1%, and 82.7% of the diet of sheep in fall, spring and summer, respectively. Sheep preferred herbaceous vegetation when available. For browse, sheep preferred oak species in fall, whereas in summer they preferred Adenostoma fasciculatum (chamise). Goats exhibited a similar species preference ranking, but with significant differences in proportions. Seasonal variations in intake proportions only partially reflected differences in nutritional quality. It is likely that seasonal variation in secondary compound concentration as well as available choice, in particular available herbaceous biomass, are important factors driving intake and diet composition. Organic matter digestibility of the consumed diets varied from 55.8% in fall to 61.9% in spring for goats and from 44.1% in fall to 56.8% in spring for sheep. Daily DM intake (g kg BW-0.75) was lowest (P < 0.05) in summer for goats and sheep but highest (P < 0.05) in fall for goats and in spring for sheep. Crude protein (g kg BW-0.75) and ME (MJ kg BW-0.75) intakes were lowest (P < 0.05) in fall for goats and in summer for sheep but highest (P < 0.01) in spring for goats and sheep. All animals lost weight throughout all seasons but sheep lost relatively more weight (P < 0.05) than goats. Under the conditions of this study, the nutritional quality of the selected diet did not suffice to maintain body condition. Goats fare relatively better under conditions of low availability of herbaceous biomass. However, adequate supplementation programs must be designed to employ small ruminants for the reduction of flammable biomass in California chaparral. (C) 2011 Elsevier B.V