Influence of forbs and shrubs on nutrient digestion and balance in sheep fed grass hay

Abstract

Eight Debouillet yearling wethers were used in a replicated 4 × 4 Latin square experiment to evaluate the influence of forb mix, a shrub mix and alfalfa (ALF) hay on nutrient utilization of a basal grass hay (GH; 1.21% N) diet. Wethers ate less ( P<0.05) of the forb diet than ALF or shrub diets, presumably because forb acceptance was substantially reduced when fed in a dried, ground form. Addition of ALF, forbs or shrubs to GH did not affect ( P>0.05) digestibility of dry matter, gross energy, or neutral detergent fiber but ADF digestibility was less ( P<0.05) for wethers fed forbs or shrubs than for those fed GH or GH+ALF. Addition of ALF or shrubs to the basal GH increased ( P<0.05) N and gross energy intakes. When adjusted to a common N intake level by covariate analysis, fecal N was less ( P<0.05) and urine N losses were greater ( P<0.05) for the shrub diet compared with GH alone or GH+forbs, but N retention was similar ( P>0.05) among all diets. Metabolizable energy (ME) values for diets in this experiment (1.23–1.45 kcal/g) were somewhat lower than those reported previously (1.6–1.9 kcal/g) for GH diets. Forb and ALF diets did not differ ( P>0.05) in ME content (1.45 and 1.40 kcal/g) and both were greater ( P<0.05) than the GH or GH+shrub diets (1.23 and 1.27 kcal/g). Based on these results, forbs and shrubs influence digestibility of most nutrients in GH in a manner similar to ALF. We conclude that shrubs and forbs used in this study can effectively serve as supplements for low-quality GH diets for livestock. Shrubs may have greater potential for improving efficiency of N utilization, whereas forb additions may potentially increase energy retention with GH diets.