Contribution of Mixtures of Three Chaparral Shrubs to the Protein and Energy Requirements of Spanish Goats1

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Abstract
Hand-harvested dried mixtures of chaparral shrubs (chamise, scrub oak and manzanita) with or without a basal diet of sudangrass and alfalfa hay (SA) were fed to Spanish goat wethers in a 4 × 4 Latin square sequence. Feed intake (grams/kilogram body weight75/day) with each diet was: SA (fed initially), 55.2; mixtures of three shrub species and SA, 47.9, and shrubs alone, 18.5. Protein/energy (P/E) values (measured as percentage of digestible energy supplied by digestible protein) were 21% for the basal diet (SA) and 13, 12 and 14% for the three mixtures of shrubs and SA (diets A, B and C). Diet D (all shrubs) had a negative P/E value, and goats fed this diet had negative N balances. No differences in in vivo digestibility were found between animals or periods, but means for dry matter digestibility of feeds, crude protein and all fiber components were different (P>.005). Digestion of diet D, which had the highest lignin to acid detergent fiber ratio, was lower (P>.01) than digestion of diets A, B and C for most nutrients. Predicted digestibilities of feeds determined by four methods - (1) fecal N index (FNI); (2 and 3) ratio techniques, sulphuric lignin (ADLS) and acid detergent insoluble ash (ADF-IA), and (4) in vitro — were compared to in vivo values. Whereas in vitro underestimated digestibilities of shrub-containing diets, the other three methods overestimated them. In vitro digestibilities of shrub diet samples collected by browsing goats were higher (P>.005) when donor goats were fed a 65% shrub diet than when they were fed a 100% alfalfa diet. Discrepancies between in vivo and markers (FNI, ADLs, ADF-IA) were due to greater recoveries of ADLS and ADF-IA in feces than in feeds. All fecal samples contained a considerable amount of soil silica. FNI appears inappropriate for estimating digestibility of shrub diets. The in vivo technique is useful if an appropriate source of inoculum is used.