Nutritive value and palatability of guajillo (Acacia berlandieri) as a component of goat diets

Guajillo (Acacia berlandieri Benth.) is a low-growing, multi-stemmed shrub widely distributed in southern Texas and northern Mexico. Proximate analysis indicates the leaves have high concentrations of nitrogen and energy suggesting that it is a potentially valuable forage resource, yet excessive consumption is believed to cause a hind-limb ataxia. The nutritive value of, and their preference for, guajillo leaves was determined in two trials using male Angora goats (8 months old, 23.7+/-1.09kg initial weight). In a metabolism trial, air-dried guajillo leaves and alfalfa hay were chopped and mixed to prepare four diets containing 0, 25, 50 and 75% of guajillo leaves, which were fed in a 4x4 Latin Square design. Animals were retained in metabolism crates for a 10 day adaptation period followed by a 7 day collection period. Diets were analyzed for DM, OM, N, NDF, ADF, ADF-N, cellulose, lignin, gross energy, phenolic amines, and bovine serum albumin precipitating capacity. Feed DM and OM intake, water consumption, fecal and urine output, nitrogen and energy balance, and urine glucuronic acid output was determined on the animals. Dietary concentration of guajillo had no effect (P>0.05) on intake (26.25+/-1.86g OM kg(-1) BW). Water intake and urine output decreased (P<0.05) with increasing guajillo in the diets, but water retention increased (P<0.05) with increasing guajillo. The digestibility of all the nutrients decreased (P<0.05) with increasing level of guajillo, with ADF digestibility reduced to zero in the 75% guajillo diet. Energy balance and nitrogen balance expressed as percent intake decreased (P<0.05) with increasing level of guajillo. Increasing ADF-N, together with reduced ADF digestibility, reduced the availability of nitrogen in the 75% guajillo diet. Phenolic amine and tannin concentrations increased (P<0.05) as level of guajillo in the diet increased. Glucuronic acid output in goats fed 75% guajillo was significantly (P<0.05) higher than the other diets, and suggests an increased requirement for liver glucose metabolism in goats consuming large amounts of guajillo. In the palatability trial, the same goats were fed 250g of each diet for 9 days in a cafeteria trial to determine the characteristics eliciting a proportional choice among the four diets. Total DMI was similar to the results of the first trial. However, intakes of particular diets decreased (P<0.05) with increasing level of guajillo. Despite an apparently desirable gross energy content of all the diets, those containing guajillo did not meet digestible energy requirements for maintenance and mohair production at moderate levels of activity and production, and although none of the diets appeared to be acutely toxic, the goats preferred the diets lower in guajillo.